Upconverting/magnetic Janus-like nanoparticles integrated into spiropyran micelle-like nanocarriers for NIR light- and pH- responsive drug delivery, photothermal therapy and biomedical imaging

The integration of multiple functionalities into single theranostic platforms offers new opportunities for personalized and minimally invasive clinical interventions, positioning these materials as highly promising tools in modern medicine. Thereby, magneto-luminescent Janus-like nanoparticles (JNPs) were developed herein, and encapsulated into near-infrared (NIR) light- and pH- responsive micelle-like aggregates (Mic) for simultaneous magnetic targeting, biomedical imaging, photothermal therapy, and pH- NIR-light activated drug delivery. The JNPs consisted of NaYF4:Yb,Tm upconverting nanoparticles (UCNPs) on which a well-differentiated magnetite structure (MNPs) grew epitaxially. JNPs were encapsulated together with doxorubicin (Dox) into micelle-like aggregates formed with the stimuli-responsive Poly(NIPAM-co-Spiropyran) copolymer, which responds to UV light, temperature changes, and pH variations, so as to form the JNP-Dox@Mic nanocarrier. Based on physicochemical characterizations, the mechanism for the NIR-activated release of Dox from the JNP-Dox@Mic aggregates is suggested: i) activation of the upconverting emissions with 975 nm light, ii) energy transfer to the material's lattice via nonradiative relaxation, inducing a local temperature increase, iii) resonance energy transfer (RET) from the UV-emission bands to the micelle-like aggregates, and iv) reversible isomerization of the hydrophobic Spiropyran (SP) moiety to a hydrophilic zwitterionic merocyanine (MC) form, leading to Dox delivery. Furthermore, the strong light-to-heat conversion ability of the JNPs was demonstrated through thermal imaging analysis, reaching temperatures up to 108 °C upon irradiation for 60 seconds. The efficacy of these nanocomposites for pH- and NIR-light-induced controlled release was demonstrated using electrophoretic separations and tested against MCF-7 breast cancer cells. While non-irradiated samples of JNP-Dox@Mic were innocuous up to 200 μg.mL-1, irradiation with 975 nm light for 5 minutes reduced cell viability to 26 %. These findings highlight the effective synergy between JNPs and micelle-like aggregates, resulting in versatile heterostructures that could be evaluated for multimodal therapy and imaging strategies.

Up-conversion emission characteristics and temperature measurement of core-shell structured NaGdF4: Er3+Tm3+/Yb3+@NaYbF4: xYb3+ (x = 25, 50) phosphors

In this study, the intensity and properties of up-conversion luminescence in core-shell structured NaGdF4: Er3+/Tm3+/Yb3+@NaGdF4: Yb3+ phosphors were investigated. After coating the NaGdF4: 0.5Er3+/0.5Tm3+/30Yb3+ (0.5Er/0.5Tm/30Yb) core with NaGdF4: xYb3+ (x = 25, 50) shells, the luminescence intensity of the phosphors was improved. The enhancement factor reached to 3.97 (x = 25) and 1.15 (x = 5) respectively. Owing to the different increase of up-conversion luminescence peak, the emission color changed from blue-green to yellowish-green in NaGdF4: 0.5Er3+/0.5Tm3+/30Yb3+@NaGdF4: 25Yb3+ (0.5Er/0.5Tm/30Yb@25Yb) phosphors. Additionally, the temperature sensing properties of the 0.5Er/0.5Tm/30Yb@25Yb phosphors were examined. A maximum relative sensitivity (Sr) of 0.013 K-1 was observed at 303 K based on florescence intensity ratio of two green emission. And a higher Sr of 0.034 K-1 was recorded at 403 K based on the ratio of green (540 nm) and near-red emissions (800 nm). These findings not only deepen the understanding of the up-conversion processes in core-shell structured phosphors but also promote the development of rare-earth ion core-shell structures for applications in temperature sensing and luminescent displays.

Near and mid-infrared emissions implications of hydroxyl groups in Er3+-doped tellurite glasses: enhancing luminescent properties via purification processes

Tellurite glasses are increasingly attracting interest from the photonics industry due to their promising spectroscopic properties. However, intrinsic absorption losses caused by impurities, especially hydroxyl groups (OH-) remain a significant challenge for achieving efficient infrared emission. This work presents what we believe to be a new purification method for Er3+-doped tellurite glasses using diethyl zinc to treat oxide precursors. Glasses with the composition 69.7 TeO2 - 25 ZnO - 5 La2O3 - 0.3 Er2O3 (mol %) were fabricated at each step of the purification and characterized. The effect of the purification in the reduction of OH content is evidenced in the decreased absorption coefficient from 2.57 to 0.22 cm-¹ at 3300 nm after applying the chemical treatment, which accounted for a decrease in the number of OH ions/cm3 from 2.88 × 1019 to 2.70 × 1018. The purification process significantly improved the optical properties, enabling consecutive emissions at 1535, 2700, and 3280 nm when pumped with an optical parametric oscillator (OPO) laser tuned to 522 nm. With the reduction of OH content, there was an increase in the emission efficiency from 78.6 to 93.9% and 7.3 to 10.7% for the emissions for 4I13/2→4I15/2 and 4I11/2→4I13/2, respectively.

Pr3+ Visible to Ultraviolet Upconversion for Antimicrobial Applications

This paper addresses the upconversion of blue light to ultraviolet-C (UVC) with Pr3+-activated materials for antibacterial applications of UVC. It discusses the processes through which UV radiation provides biocidal effects on microorganisms, along with the most popular UVC sources employed in these processes. We describe the electronic and optical properties of the Pr3+ ion, emphasizing the conditions the host material must meet to obtain broad and intense emission in the UVC from parity-allowed transitions from the 4f5d levels and provide a list of materials that fulfill these conditions. This paper also delineates lanthanide-based upconversion, focusing on Pr3+ blue to UVC upconversion via the 3P0 and 1D2 intermediate states, and suggests routes for improving the quantum efficiency of the process. We review literature related to the use of upconversion materials in antimicrobial photodynamic treatments and for the blue to UVC upconversion germicidal effects. Further, we propose the spectral overlap between the UVC emission of Pr3+ materials and the germicidal effectiveness curve as a criterion for assessing the potential of these materials in antimicrobial applications. Finally, this paper briefly assesses the toxicity of materials commonly used in the preparation of upconversion materials.

Bright upconversion over extended temperatures enabled by an organic surface layer

Lanthanide-doped nanocrystals are promising for photon frequency upconversion with substantial spectrum tunability. However, the utilization of the upconversion process has been constrained by low luminescence efficiency, which may further attenuate at elevated temperatures due to thermal quenching. Herein, we report a versatile strategy to boost upconversion luminescence across a wide temperature range by surface coordination of small organic molecules. Mechanistic investigations affirm that the organic surface layer passivates defects and isolates high-energy surface oscillators, thereby preventing the dissipation of excitation energy. The energy preserving effect becomes more prominent with increasing temperatures, especially in a humid environment. Accordingly, the upconversion emission of NaGdF4:Yb3+/Tm3+ nanocrystals is substantially enhanced in the ambient environment after ligand coordination, accompanied by an additional emission augmentation with increasing temperature to 443 K. By leveraging this anomalous optical response to thermal stimuli, we further establish full-color thermochromic upconversion switching for advanced anti-counterfeiting and logic encryption technologies.

Chiral Mesostructured Yb3+, Er3+ Codoped CeO2 with Upconverted Circularly Polarized Luminescence

Upconverted circularly polarized luminescence (UC-CPL) active organic and organic-inorganic composite materials have garnered increasing attention due to their vast potential applications in areas such as 3D displays, encryptions, spintronics and optoelectronic devices. However, effective methods for fabricating chiral inorganic materials exhibiting UC-CPL remain a challenge. Herein, we propose an approach for the synthesis of UC-CPL active chiral mesostructured CeO2 powders (CMCs) via a hydrothermal growth method, using L/D-aspartic acid as symmetry-breaking and structure-directing agents. Two levels of chirality exist in CMCs: primary nanoplates constructed from nanoparticles and the helical stacking of these nanoplates to form a twisting nanofusiform. Yb3+ and Er3+ ions can be codoped into the CMCs through a one-step synthesis to achieve UC-CPL. The 1 % Yb3+, 1 % Er3+ codoped CMCs exhibited absorption-based optical activities in the range of 350-500 nm, similar to undoped CMCs, and displayed circularly polarized luminescence in the range of 520-610 nm under the excitation by a 980 nm laser. This luminescence is attributable to the energy transfer process between Yb3+ and Er3+. This work may provide new insights into designing chiral photon upconversion inorganic materials.

Synergistic Integration of Halide Perovskite and Rare-Earth Ions toward Photonics

Halide perovskites (HPs), emerging as a noteworthy class of semiconductors, hold great promise for an array of optoelectronic applications, including anti-counterfeiting, light-emitting diodes (LEDs), solar cells (SCs), and photodetectors, primarily due to their large absorption cross section, high fluorescence efficiency, tunable emission spectrum within the visible region, and high tolerance for lattice defects, as well as their adaptability for solution-based fabrication processes. Unlike luminescent HPs with band-edge emission, trivalent rare-earth (RE) ions typically emit low-energy light through intra-4f optical transitions, characterized by narrow emission spectra and long emission lifetimes. When fused, the cooperative interactions between HPs and REs endow the resulting binary composites not only with optoelectronic properties inherited from their parent materials but also introduce new attributes unattainable by either component alone. This review begins with the fundamental optoelectronic characteristics of HPs and REs, followed by a particular focus on the impact of REs on the electronic structures of HPs and the associated energy transfer processes. The advanced synthesis methods utilized to prepare HPs, RE-doped compounds, and their binary composites are overviewed. Furthermore, potential applications are summarized across diverse domains, including high-fidelity anticounterfeiting, bioimaging, LEDs, photovoltaics, photodetection, and photocatalysis, and conclude with remaining challenges and future research prospects.

Zinc Doping-Induced Lattice Growth Regulation for Enhanced Upconversion Emission in Serum Bilirubin Detection

Upconversion nanoparticles (UCNPs) hold significant potential in the detection of disease biomarkers in serum due to their ability to avoid fluorescence background interference. The design of upconversion probes with a high emission intensity is particularly critical for enhancing the accuracy and sensitivity of visual detection. Herein, we achieved highly efficient luminescent upconversion nanocrystals by enhancing the internal energy transfer efficiency of the nanoparticles through zinc-ion doping, which induced a lattice growth transformation. The nanocrystals can greatly enhance the fluorescence emission intensity while keeping the fluorescence color unchanged. Additionally, a 980 nm near-infrared excited upconversion visual sensing platform was constructed for serum bilirubin detection. By a combination of UCNPs with sulfosalicylic acid (SSA) and iron ions to form an efficient upconversion nanoprobe, fluorescence and colorimetric gradient changes can be observed in the presence of bilirubin. This enables highly sensitive colorimetric and fluorescence detection of bilirubin, with a detection limit as low as 21.4 nM in fluorescence mode. Clinical serum sample tests indicate that the sensor possesses excellent selectivity and anti-interference capability, accurately detecting bilirubin in complex biological matrices. This study exhibits strong upconversion luminescence (UCL) emission and demonstrates the potential for early diagnosis of diseases through high-sensitivity biomarker detection.

Upconversion/Downshifting Circularly Polarized Luminescence over 1200 nm in a Single Nanoparticle for Optical Anticounterfeiting and Information Encryption

Multimodal upconversion and downshifting circularly polarized luminescent materials hold significant potential for optical anticounterfeiting applications due to their exceptional chiroptical properties. However, constructing these materials within a single emitter remains challenging. In this study, a conceptual model of multimodal upconversion/downshifting circularly polarized luminescence (CPL) is realized within a single nanoparticle. A new type of nanoparticles with multilayer core-shell architecture is fabricated, capable of delivering upconversion/downshifting luminescence, when excited by a 980 nm laser. Utilizing a co-assembly strategy, multimodal upconversion/downshifting CPL emission, covering a broad emission range from ultraviolet (UV) to the second near-infrared (NIR-II) region, can be realized at the supramolecular level. These chiroptical properties closely follow the chirality of host matrix and are strongly dependent on the distribution mode of nanoparticles within the matrix films. The multimodal upconversion/downshifting CPL behavior enabled cutting-edge encryption applications including optical anticounterfeiting and information encryption. This work introduces a novel approach to designing multimodal upconversion/downshifting CPL materials and opens new avenues for the development of chiroptical functional materials.

Dye-sensitized upconversion nanoprobes with ultra-high signal-to-background ratio for visual and sensitive detection of nerve agent mimics

An exciting upconversion nanoprobe conditioning strategy is proposed to improve the signal-to-background ratio (SBR) through a dye-sensitized strategy, in which the dye functions both as a recognition unit of the detection target and as a sensitizer to amplify the visible luminescence of the lanthanide-doped upconversion nanoparticles (UCNPs), instead of a quencher. The application of this dye-sensitized upconversion nanoprobe to the visual detection of nerve agent mimics diethoxy phosphatidylcholine (DCP) showed excellent detection performance, with up to 110-fold enhancement of the luminescence response of the probe in DCP solution and a detection limit as low as 2 nM. Finally, we performed visual detection of DCP solution and vapor by using test strips containing the probe. It is promising to apply the probe to monitor the leakage of DCP in the real environment.

Unlocking advanced thermometric capabilities: BiVO4: Er3+/Yb3+ nanophosphors with dual-mode up-conversion and down-shifting features

Luminescent materials doped with rare-earth (RE) ions have emerged as powerful tools in thermometry, offering high sensitivity and accuracy. However, challenges remain, particularly in maintaining efficient luminescence at elevated temperatures. This study investigates the thermometric properties of BiVO4: Yb3+/Er3+ (BVO: Er/Yb) nanophosphors synthesized via the sol-gel method. Structural, morphological, and optical analyses confirm the high purity and monoclinic crystal structure of the materials. Dual-mode luminescence under UV and near-infrared (NIR) excitation is explored, revealing complex thermal dynamics. The distinct performances of these luminescent thermometers, in terms of thermal sensitivity and temperature uncertainty, were evaluated in the non-saturation regime in both down-shifting (DS) and up-conversion (UC) processes. Utilizing fluorescence intensity ratio (LIR) measurements, we quantified absolute and relative sensitivities, as well as temperature uncertainties, over a temperature range of 300-450 K. Temperature sensing was based on the LIR of green emission bands arising from the thermally coupled 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2 transitions of Er3+. The maximum absolute sensitivity (S a) reached 60 × 10-4 K-1 at 388 K under 975 nm excitation (UC) and 56 × 10-4 K-1 at 400 K under 325 nm excitation (DS). Notably, for both excitation modes, the relative sensitivity (S r) decreased consistently with increasing temperature, peaking at 0.908% K-1 and 0.87% K-1 at 300 K, and gradually declining to 0.4% K-1 and 0.39% K-1 at 450 K for the DS and UC processes, respectively. Temperature resolution (δT) also varied with temperature, increasing from 0.55 K to 1.23 K as the temperature rose from 300 to 450 K under 325 nm excitation. A comparable trend was observed for δT under 975 nm excitation. These findings underscore the potential of BVO: Er/Yb nanophosphors as versatile and effective luminescent thermometers for a broad range of applications.

Upconversion-Linked Immunosorbent Assay for the Biomimetic Detection of the Mycotoxin Cyclopiazonic Acid

The neurotoxin α-cyclopiazonic acid (CPA) is an emerging mycotoxin produced as a secondary metabolite by several fungi species (i.e., Penicillium spp. and Aspergillus spp.). CPA commonly contaminates maize, crops, cheese, and wine. In this work, CPA detection in foodstuff was accomplished by the innovative integration of two strategies: upconversion nanoparticles (UCNPs) and epitope-mimicking peptides, to develop a competitive upconversion-linked immunosorbent assay (ULISA). We have applied UCNPs (type NaYF4:Yb3+, Er3+) as background-free optical labels due to their anti-Stokes shift with excitation in the near-infrared region and emission in the ultraviolet-visible region. Moreover, a CPA epitope-mimicking cyclic peptide (A2) was used as a substitute for the toxin-conjugates traditionally applied to competitive assays. UCNPs were decorated with an anti-CPA fragment antigen-binding antibody (UCNP-Fab), and CPA detection was achieved through competition with a biotinylated CPA epitope-mimicking cyclic peptide (A2-biotin, ACNWWDLTLC-GGGSK (Biotin)-NH2), anchored to a streptavidin-coated microtiter plate, for antibody binding. The ULISA platform offers ultrasensitive detection of CPA (limit of detection of 1.3 pg mL-1 and IC50 value of 15 pg mL-1), and no cross-reactivity was observed with other coproduced mycotoxins. These results substantially outperformed the analytical features of conventional heterogeneous immunoassays based on enzymatic detection. Additionally, the use of advanced computational tools, such as MOE and Alphafold AI, proved advantageous in elucidating the molecular interactions between the antibody and the epitope, providing insights that enhance the rational design of immunoassays. The proposed ULISA was applied to detect CPA in spiked maize samples, and the results were validated by high-performance liquid chromatography coupled to a tandem mass spectrometry detector (HPLC-MS/MS).

Three‐Photon Upconversion Luminescence of Gd2O2S: Ho3+, Er3+ for High‐Sensitivity FIR Thermometer and Multimode Anti‐Counterfeiting

The performance control and multidimensional applications of upconversion phosphor have become the hotspot and difficulty in current research and application due to the complex luminescence mechanism. Based on the efficient Gd2O2S: Er3+ upconversion luminescence of 1550 nm excitation and design strategy for co‐doped materials, the multicolor (light green to red) and multifunctional upconversion phosphor Gd2O2S: Er3+, Ho3+ is successfully prepared. Benefiting from the clear mechanism of three‐photon upconversion and energy transfer after co‐doping, the novel applications of Gd2O2S: Er3+, Ho3+ can greatly be expanded. This phosphor can be well used as a fluorescence thermometer due to the higher sensitivity (2.46% K−1@170 K), wider temperature sensing range (170–267 K, Sr > 1% K−1), and greater color variation (Δx = 0.2416, Δy = 0.2483) relative to Gd2O2S: Er3+ and other same type of material. In addition, multiple patterns and encoded outputs are also effectively achieved by the combination of phosphors under multiple light stimuli response. This shows the greater application potential of phosphor in the fields of anti‐counterfeiting and information encryption. This study can also provide a new view to study the more high‐performance and multifunctional upconversion phosphor.

Long-Term Stable Eu2O3-Loaded Dendritic Mesoporous Silica Nanoprobes with Coordination-Enhanced Photoluminescence for Ultrasensitive Lateral Flow Immunoassay

Inorganic lanthanide nanomaterials as photoluminescent biolabels have attracted increasing attention due to their superior physicochemical properties. However, unstable conjugation of inorganic lanthanide nanomaterials with biological function units (such as antibodies) induces instability of conjugated complexes in aqueous solution, limiting their clinical application. In this study, we developed a rapid point-of-care testing (POCT) platform strategy based on coordination-enhanced time-resolved luminescence of specially nanostructural lanthanide particles for lateral flow immunoassay (CE-TRFIA). This strategy integrates a nanoprobe via a dendritic mesoporous silica nanosphere (DMSN) loading a large amount of ultrasmall amorphous europium oxide (Eu2O3) nanoparticles, which rapidly dissolve to release Eu3+ cations under neutral pH value and form luminescent complexes with photosensitizers (such as β-NTA and TOPO) in an LFIA system. This innovative strategy achieves high-sensitivity detection and long-term stability primarily through high-loading probes, excellent dissolution enhancement, stable covalent coupling, and time-resolved detection. With Procalcitonin (PCT) antigen selected as the detection sample, this approach achieves high-sensitivity detection of PCT with a limit of detection (LoD) as low as 1.9 pg/mL, significantly lower than that of commercial LFIA (0.1 ng/mL), and excellent clinical correlation (r = 0.989). The method offers chemiluminescence-level sensitivity without the need for large instruments while retaining the real-time detection characteristics of LFIA. Our results highlight CE-TRFIA as a highly sensitive, specific, and rapid POCT solution for detecting low-abundance biomarkers such as PCT, enhancing the diagnostic capabilities of traditional LFIA and offering significant potential for ultrasensitive and rapid clinical diagnostics.

Triple-Mode Protection with Ln3+ Ion-Doped Core-Heptad-Shell Single Nanocrystals for High-Level Security Applications

In this work, oleic acid (OA)-capped core-heptad-shell (CHS) nanocrystals (NCs) that exhibit multiple emissions achieved through downshifting and orthogonal upconversion are synthesized via layer-by-layer thermal decomposition. This method enables the downshifting process to be accommodated by doping ions in the inert space between two upconversion patterns (the core and fourth shell) and doping Ce/Tb or Ce/Eu ions in the NaGdF4 layer for the first time. These developed CHS NCs exhibit different emission colors via 980 and 800 nm orthogonal upconversion and downshifting emissions under 256 nm UV excitation in hexane solvent. Furthermore, surface-functionalized OA is removed using mild acid treatment. The resulting bare CHS NCs disperse well in water and exhibit 21.60-fold and 43.59-fold higher Ce/Tb and Ce/Eu luminescence intensities, respectively, than the OA-capped CHS NCs. These NCs are mixed with a carboxymethylcellulose (CMC) polymer in an aqueous medium to form a CMC-CHS NC gel. Invisible patterns and QR codes are printed on nonfluorescent paper using gels and screen-printing techniques. These patterns and QR codes exhibit three different emission colors under three different excitations. This method can be used for high-level anticounterfeiting applications.

Dynamic Rare-Earth Metal-Organic Frameworks Based on Molecular Rotor Linkers with Efficient Emissions and Ultrasensitive Optical Sensing Performance

4,4',4″-Triphenylamine tricarboxylate (TPA-COOH) with a distinct molecular rotor structure was reacted with rare-earth (RE) metal ions to obtain seven dynamic RE-based luminescent MOFs (RE-LMOFs) (i.e., emission colors in the blue, yellow-green, red, and near-infrared regions and emission peak wavelengths between 400 and 1600 nm) via the effective transfer of absorbed energy from TPA-COOH to the RE metal ions through the antenna effect. Due to the large energy level difference between RE ions, it was rare in the early days to use the same ligand to construct energy-level matching RE-LMOF homologues with multiple RE metal centers. The uncoordinated oxygen atoms on the molecular rotor linkers in RE-LMOFs provide active sites that can specifically capture highly toxic metal ions and strong oxidative pollutants. The limit of detection (LOD) of RE-LMOF for Al(III) ions is far below the maximum concentration of Al(III) ions in drinking water stipulated by the U.S. Environmental Protection Agency (USEPA) and that for H2O2 is much lower than the H2O2 content in cancer cells, showing excellent application potential for diagnosing early cell cancelation.

Upconversion Luminescence in a Photostable Ion-Paired Yb-Eu Heteronuclear Complex

Lanthanide-based upconversion molecular complexes have potential application in diverse fields and attracted considerable research interest in recent years. However, the similar coordination reactivity of lanthanide ions has constrained the designability of target molecule with well-defined structure, and many attempts obtained statistical mixtures. Herein, an ion-paired Yb-Eu heteronuclear complex [Eu(TpPy)2][Yb(ND)4] (TpPy=tris[3-(2-pyridyl)pyrazolyl]hydroborate, ND=3-cyano-2-methyl-1,5-naphthyridin-4-olate) was designed and synthesized. Thanks to the radius difference between Eu3+ (1.07 Å) and Yb3+ (0.98 Å) ions, the hexadentate TpPy ligand was selected to coordinate with Eu3+ and the Yb3+ with a smaller radius was chelated by bidentate ND ligand. As a result, the sites of Eu3+ and Yb3+ in the complex can be clarified by high-resolution mass spectrometry and single-crystal structure analysis. Upon the excitation of Yb3+ at 980 nm, the upconversion emission of Eu3+ was realized through a cooperative sensitization process. Furthermore, [Eu(TpPy)2][Yb(ND)4] demonstrated excellent photostability during continuous high-power density 980 nm laser irradiation, with a LT95 (the time to 95 % of the initial emission intensity) of 420 minutes. This work provides the first example of a pure ion-paired Yb-Eu heteronuclear complex upconversion system and may bring insights into rational design of lanthanide-based upconversion molecular complexes.

Nitric Oxide-Photodelivering Materials with Multiple Functionalities: From Rational Design to Therapeutic Applications

The achievement of materials that are able to release therapeutic agents under the control of light stimuli to improve therapeutic efficacy is a significant challenge in health care. Nitric oxide (NO) is one of the most studied molecules in the fascinating realm of biomedical sciences, not only for its crucial role as a gaseous signaling molecule in the human body but also for its great potential as an unconventional therapeutic in a variety of diseases including cancer, bacterial and viral infections, and neurodegeneration. Handling difficulties due to its gaseous nature, reduced region of action due to its short half-life, and strict dependence of the biological effects on its concentration and generation site are critical questions to be solved for appropriate therapeutic uses of NO. Light-activatable NO precursors, namely, NO photodonors (NOPDs), address the above issues since they are stable in the dark and permit in a noninvasive fashion the remote-controlled delivery of NO on demand with great spatiotemporal precision. Engineering biocompatible materials with NOPDs and their combination with additional imaging, therapeutic, and phototherapeutic components leads to intriguing light-responsive multifunctional constructs exhibiting promising potential for biomedical applications. This contribution illustrates the most significant progress made over the last five years in achieving engineered materials including nanoparticles, gels, and thin films, sharing the common feature to deliver NO under the exclusive control of the biocompatible visible/near infrared light inputs. We will highlight the logical design behind the fabrication of these systems, illustrating the potential therapeutic applications with particular emphasis on cancer and bacterial infections.

Specific smart sensing of electron-rich antibiotics or histidine improves the antenna effect, luminescence, and photodynamic sterilization capabilities of lanthanide polyoxometalates

Excessive discharge of antibiotics seriously threatens human health and is thus a global public health problem. This highlights the urgent need to develop intelligent sensing materials for specific antibiotics that are highly visual, fast, convenient, and inexpensive. Herein, two reverse α-octamolybdate polyoxometalates (POMs; Mo8) were used to chelate lanthanide ions to obtain lanthanide POMs (LnPOMs; LnMo16; Ln = Eu, Sm, Tb, Gd) with highly sensitive smart photoresponses to specific antibiotics (ofloxacin [OFN], norfloxacin [NOR], enrofloxacin [ENR], and oxytetracycline [OTC]) and histidine (His) with luminescence turn-on. Specific antibiotics and His, which has an electron-rich structure, can efficiently enhance the antenna effect, thereby greatly improving the luminescence of EuMo16. Surprisingly, OFN and NOR both enhanced the luminescence of Eu(III) ions and Mo8, whereas ENR and OTC only enhanced the luminescence of Eu(III) ions, showing a differentiated sensitization effect. More notably, the combination of POMs and Ln(III) ions enhanced the ability of LnPOMs to produce reactive oxygen species under light irradiation, and these LnPOMs showed significant sterilization effects on Escherichia coli and Staphylococcus aureus. To our knowledge, this is the first time electron-rich antibiotics or amino acids were used to enhance the luminescence of LnPOMs, achieving luminescence-enhanced photoresponse to specific antibiotics and amino acids.

Laser Characteristics of Er3+/Yb3+:K-BaF2-Al-Phosphate Glasses

Er3+ and Er3+/Yb3+-doped phosphate-based glasses have been synthesized by melt quenching technique and are characterized by absorption spectra, infrared emission, decay curves, Fourier transform infrared spectrum and up-conversion studies. From the absorption spectra, intensity parameters and radiative properties have been derived utilizing the Judd-Ofelt theory. Er3+-doped glass is found to have larger radiative lifetime for the laser originating from 4I13/2 level at 1537 nm. Infrared and visible characteristic emissions have been measured by exciting at 790 nm through down- and up-conversion, respectively. The up-conversion spectra consist of intense green emission at around 525 and 545 nm ascribed to the 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2 transitions, respectively, and a weak red emission at around 656 nm due to the 4F9/2 → 4I15/2 transition of Er3+ ions. Various spectroscopic and laser characteristics of these glasses have been calculated and compared with those of similar reported ones.

An Integrated Nanoplatform via Dual Channel Excitation for Both Precise Fluorescence Imaging and Photodynamic Therapy of Orthotopic Breast Tumor in NIR-II Region

Although research on photodynamic therapy (PDT) of malignant tumor has made considerable progress in recent years, it is a remaining challenge to extend PDT to the second near-infrared window (NIR-II) along with real-time and accurate NIR-II fluorescence imaging to determine drug enrichment status and achieve high treatment efficacy. In this work, lanthanide nanoparticles (Ln NPs)-based nanoplatform (LCR) equipped with photosensitizer Chlorin e6 (Ce6) and targeting molecular NH2-PEG1000-cRGDfK are developed, which can achieve NIR-II photodynamic therapy (PDT) and NIR-II fluorescence imaging by dual channel excitation. Under 808 nm excitation, Nd3+ in the outer layer can absorb the energy and transfer inward to emit strong NIR-II emissions (1064 and 1525 nm). Due to the low background noise of NIR-II light and the targeting effect of NH2-PEG1000-cRGDfK, LCR can recognize tiny tumor tissue (≈3 mm) and monitor drug distribution in vivo. Under 1530 nm excitation, internal Er3+ can be self-sensitized, generating intense upconversion emission (662 nm) that can effectively activate Ce6 for in vivo PDT due to the deep tissue penetration of NIR-II light. This study provides a paradigm of theranostic nanoplatform for both real-time fluorescence imaging and PDT of orthotopic breast tumor in NIR-II window.

The evolution of immune profiling: will there be a role for nanoparticles?

Immune profiling provides insights into the functioning of the immune system, including the distribution, abundance, and activity of immune cells. This understanding is essential for deciphering how the immune system responds to pathogens, vaccines, tumors, and other stimuli. Analyzing diverse immune cell types facilitates the development of personalized medicine approaches by characterizing individual variations in immune responses. With detailed immune profiles, clinicians can tailor treatment strategies to the specific immune status and needs of each patient, maximizing therapeutic efficacy while minimizing adverse effects. In this review, we discuss the evolution of immune profiling, from interrogating bulk cell samples in solution to evaluating the spatially-rich molecular profiles across intact preserved tissue sections. We also review various multiplexed imaging platforms recently developed, based on immunofluorescence and imaging mass spectrometry, and their impact on the field of immune profiling. Identifying and localizing various immune cell types across a patient's sample has already provided important insights into understanding disease progression, the development of novel targeted therapies, and predicting treatment response. We also offer a new perspective by highlighting the unprecedented potential of nanoparticles (NPs) that can open new horizons in immune profiling. NPs are known to provide enhanced detection sensitivity, targeting specificity, biocompatibility, stability, multimodal imaging features, and multiplexing capabilities. Therefore, we summarize the recent developments and advantages of NPs, which can contribute to advancing our understanding of immune function to facilitate precision medicine. Overall, NPs have the potential to offer a versatile and robust approach to profile the immune system with improved efficiency and multiplexed imaging power.

Ultrasensitive and Adjustable Nanothermometers Based on Er3+-Sensitized Core@Shell Nanoparticles for Use in the First Biological Window

In recent years, intensive research has focused on lanthanide-doped nanoparticles (NPs) used as noncontact temperature sensors, particularly in nanomedicine. These NPs must be capable of excitation and emission within biological windows, where biological materials usually show better transparency for radiation. In this article, we propose that NPs sensitized with Er3+ ions can be applied as temperature sensors in biological materials. We synthesized the NPs through a reaction in high-boiling solvents and confirmed their crystal structure and the formation of core@shell NPs by using X-ray diffraction, high-resolution transmission electron microscopy, and element distribution mapping within the NPs. NaErF4@NaYF4, NaYF4:12.5% Er3+, 2.5% Tm3+@NaYF4, NaYF4:7.5% Er3+@NaYF4, and NaYF4:12.5% Er3+, 2.5% Ho3+@NaYF4 exhibited intense upconversion (UC) emission under 1532 nm laser excitation detectable also in the whole human blood. We propose that this UC results from energy transfer between Er3+ ions and from Er3+ to Tm3+ or Ho3+ codopants. To determine the mechanism of UC, we measured the dependence of the emission band intensities on the laser power densities. Importantly, we also analyzed the temperature-dependent emission of the NPs within the 295-360 K range. Based on the collected emission spectra, we calculated the luminescence intensity ratios (LIRs) of the emission bands to assess their potential for optical temperature sensing. The temperature-sensing properties varied with the concentration of Er3+ ions and the presence of additional Tm3+ or Ho3+ codopants. Depending on the NP composition and the emission bands used for luminescence ratio calculations, the maximum relative temperature sensitivity ranged from 4.55%·K-1 to 1.12%·K-1, with temperature resolution between 0.05 and 2.53 K at room temperature. Finally, as proof of using NPs as temperature sensors in biomedicine, we successfully measured the temperature-dependent emission of NaYF4:7.5% Er3+@NaYF4 NPs dispersed in whole blood under 1532 nm excitation. We demonstrated that the ratio of Er3+ ion emission bands changes with temperature, indicating that these NPs have potential applications in temperature sensing within biological environments. We also confirmed the properties of NPs as temperature sensors by measuring the temperature reading uncertainty and the repeatability of the LIR readings during heating-cooling cycles, thereby confirming the excellent properties of the studied systems as temperature sensors.

Distortion Engineering: A Strategy to Modulate Molecular Upconversion with Molecular Cluster-Aggregates

The rational engineering of molecules is a powerful chemistry tool of pivotal importance in the fields of molecular magnetism and luminescence. Hence, systems that can be modulated via molecular engineering and composition control are expected to present extra versatility regarding the tunability of their properties. This is the case with molecular cluster aggregates (MCAs), high nuclearity molecular compounds. Herein, we demonstrate how the union of both strategies, namely, composition control and molecular engineering, can be employed to enhance molecular upconversion in MCAs. This was achieved by doping a {Gd8Er2Yb10} MCA with CeIII ions. By replacement of the optically silent GdIII ions with CeIII, the upconversion mechanism is modified due to CeIII-mediated cross-relaxation. In addition to this effect, we could also engineer the degree of metal site distortion due to the larger size of CeIII ions, relaxing the selection rules and impacting the upconversion quantum yield and luminescent thermometry. Opto-structural correlations demonstrate that the presented molecular engineering strategy can be used to enhance the performance of molecular upconverters.

Lanthanide ion-doped upconversion nanoparticles for low-energy super-resolution applications

Energy-intensive technologies and high-precision research require energy-efficient techniques and materials. Lens-based optical microscopy technology is useful for low-energy applications in the life sciences and other fields of technology, but standard techniques cannot achieve applications at the nanoscale because of light diffraction. Far-field super-resolution techniques have broken beyond the light diffraction limit, enabling 3D applications down to the molecular scale and striving to reduce energy use. Typically targeted super-resolution techniques have achieved high resolution, but the high light intensity needed to outperform competing optical transitions in nanomaterials may result in photo-damage and high energy consumption. Great efforts have been made in the development of nanomaterials to improve the resolution and efficiency of these techniques toward low-energy super-resolution applications. Lanthanide ion-doped upconversion nanoparticles that exhibit multiple long-lived excited energy states and emit upconversion luminescence have enabled the development of targeted super-resolution techniques that need low-intensity light. The use of lanthanide ion-doped upconversion nanoparticles in these techniques for emerging low-energy super-resolution applications will have a significant impact on life sciences and other areas of technology. In this review, we describe the dynamics of lanthanide ion-doped upconversion nanoparticles for super-resolution under low-intensity light and their use in targeted super-resolution techniques. We highlight low-energy super-resolution applications of lanthanide ion-doped upconversion nanoparticles, as well as the related research directions and challenges. Our aim is to analyze targeted super-resolution techniques using lanthanide ion-doped upconversion nanoparticles, emphasizing fundamental mechanisms governing transitions in lanthanide ions to surpass the diffraction limit with low-intensity light, and exploring their implications for low-energy nanoscale applications.

Tailoring upconversion fluorescence of lanthanide doped nanocrystals by coupling to single microcavity mode with specific symmetry

Lanthanide-doped upconversion nanoparticles have unique optical properties that can absorb low-energy infrared photons and then emit higher-energy visible ones, which have been widely used for advanced optical sensors and fluorescent probes. Efficiently tailoring the upconversion emission is desirable for meeting the wavelength requirement in various application fields. However, up to now, optimizing the composition combining with core/shell structure is still the predominant way to reach this goal. Here, we show that the relative intensities of the emission peaks of upconverting nanoparticles can be tuned by coupling to single microcavity mode with specific symmetry. Theoretical calculation based on the finite-difference time-domain (FDTD) indicates that the symmetries of the microcavity modes dominate their resonant absorption properties in the visible region. As a result, the upconversion emission peaks vary in these microcavities with different symmetries. This route can be developed for tailoring the emission spectra of other luminescent materials, such as quantum dots and fluorescent dyes.

Upconversion Nanoparticles Based Sensing: From Design to Point-of-Care Testing

Rare earth-doped upconversion nanoparticles (UCNPs) have achieved a wide range of applications in the sensing field due to their unique anti-Stokes luminescence property, minimized background interference, excellent biocompatibility, and stable physicochemical properties. However, UCNPs-based sensing platforms still face several challenges, including inherent limitations from UCNPs such as low quantum yields and narrow absorption cross-sections, as well as constraints related to energy transfer efficiencies in sensing systems. Therefore, the construction of high-performance UCNPs-based sensing platforms is an important cornerstone for conducting relevant research. This work begins by providing a brief overview of the upconversion luminescence mechanism in UCNPs. Subsequently, it offers a comprehensive summary of the sensors' types, design principles, and optimized design strategies for UCNPs sensing platforms. More cost-effective and promising point-of-care testing applications implemented based on UCNPs sensing systems are also summarized. Finally, this work addresses the future challenges and prospects for UCNPs-based sensing platforms.

Highly Efficient and Thermally Durable Luminescence of 1D Eu3+ Coordination Polymers with Arsenic Bridging Ligands

In this work, bisarsine oxides were evaluated as novel bridging ligands, aiming to develop practical and efficient luminescent lanthanide coordination polymers. We have synthesized one-dimensional (1D) Eu3+ coordination polymers that incorporate bisarsine oxide bridging ligands and hexafluoroacetylacetonate anions. These polymers exhibited a denser packing of chains compared to analogous polymers bridged with bisphosphine oxides. The coordination polymers demonstrated exceptional thermal stability and substantial emission quantum yields. Additionally, the bisarsine oxides induced a pronounced polarization effect, facilitating a sensitive electric dipole transition that yields considerably narrow band red emission. Remarkably, the Eu3+ coordination polymers with bisarsine oxides maintained intense emission even at 550 K. A distinctive feature of these polymers is their heating-induced emission enhancement observed when the temperature was increased from 300 K to 400 K.

Lanthanide MOFs based portable fluorescence sensing platform: Quantitative and visual detection of ciprofloxacin and Al3

In the current context of water environmental monitoring and pollution control, there's a crucial need for rapid and simple methods to detect multi-pollutant. We herein report an easy one-step hydrothermal synthesis method to produce Eu-based metal-organic frameworks (Eu MOFs), which was used as a fluorescent probe to detect the aquatic environmental pollutants of ciprofloxacin (CIP) and aluminum ions (Al3+). This fluorescent sensor enabled the cascade detection of CIP and Al3+ through fluorescence enhancement and ratio fluorescence response, respectively. The introduction of CIP significantly turned on the characteristic fluorescence of Eu MOFs at 595 nm and 616 nm through the "antenna effect". Based on this, the sensor enables quantitative detection of CIP within a linear range of 0-120 μM with a LOD as low as 50.421 nM. In the presence of Al3+, the fluorescence emission of Eu MOFs-CIP was sharply turned off due to strong Al3+ coordination with CIP, while the blue fluorescence emission of CIP was remarkably enhanced. And thus allowing ratio fluorescence quantitative detection of Al3+ (LOD = 2.681 μM). The introduction of CIP and Al3+ in cascade resulted in distinct fluorescence color changes from colorless to red and eventually to blue, exhibiting pronounced fluorescence characteristics. This observable phenomenon enables the visual detection of CIP and Al3+ in both aqueous phase and paper test strips. By combining the analysis of fluorescence chromaticity with the use of a smartphone, the fluorescence color of test papers allows for simple quantitative determination, which provides a convenient and accessible approach for quantifying CIP and Al3+ in water environments.

ZnAl2O4:Er3+ Upconversion Nanophosphor for SPECT Imaging and Luminescence Modulation via Defect Engineering

This work reports an "all-in-one" theranostic upconversion luminescence (UCL) system having potential for both diagnostic and therapeutic applications. Despite considerable efforts in designing upconversion nanoparticles (UCNPs) for multimodal imaging and tumor therapy, there are few reports investigating dual modality SPECT/optical imaging for theranostics. Especially, research focusing on in vivo biodistribution studies of intrinsically radiolabeled UCNPs after intravenous injection is of utmost importance for the potential clinical translation of such formulations. Here, we utilized the gamma emission from 169Er and 171Er radionuclides for the demonstration of radiolabeled ZnAl2O4:171/169Er3+ as a potent agent for dual-modality SPECT/optical imaging. No uptake of radio nanoformulation was detected in the skeleton after 4 h of administration, which evidenced the robust integrity of ZnAl2O4:169/171Er3+. Combining the therapeutics using the emission of β- particulates from 169Er and 171Er will be promising for the radio-theranostic application of the synthesized ZnAl2O4:169/171Er3+ nanoformulation. Cell toxicity studies of ZnAl2O4:1%Er3+ nanoparticles were examined by an MTT assay in B16F10 mouse melanoma cell lines, which demonstrated good biocompatibility. In addition, we explored the mechanism of UCL modulation via defect engineering by Bi3+ codoping in the ZnAl2O4:Er3+ upconversion nanophosphor. The UCL color tuning was successfully achieved from the red to the green region as a function of Bi3+ codoping concentrations. Further, we tried to establish a correlation of UCL tuning with the intrinsic oxygen and cation vacancy defects as a function of Bi3+ codoping concentrations with the help of electron paramagnetic resonance (EPR) and positron annihilation lifetime spectroscopy (PALS) studies. This study contributes to building a bridge between nature of defects and UC luminescence that is crucial for the design of advanced UCNPs for theranostics.

Aggregation induced emission dynamic chiral europium(III) complexes with excellent circularly polarized luminescence and smart sensors

The synthesis of dynamic chiral lanthanide complex emitters has always been difficult. Herein, we report three pairs of dynamic chiral EuIII complex emitters (R/S-Eu-R-1, R = Et/Me; R/S-Eu-Et-2) with aggregation-induced emission. In the molecular state, these EuIII complexes have almost no obvious emission, while in the aggregate state, they greatly enhance the EuIII emission through restriction of intramolecular rotation and restriction of intramolecular vibration. The asymmetry factor and the circularly polarized luminescence brightness are as high as 0.64 (5D0 → 7F1) and 2429 M-1cm-1 of R-Eu-Et-1, achieving a rare double improvement. R-Eu-Et-1/2 exhibit excellent sensing properties for low concentrations of CuII ions, and their detection limits are as low as 2.55 and 4.44 nM, respectively. Dynamic EuIII complexes are constructed by using chiral ligands with rotor structures or vibration units, an approach that opens a door for the construction of dynamic chiral luminescent materials.

Dual second harmonic generation and up-conversion photoluminescence emission in highly-optimized LiNbO3 nanocrystals doped and co-doped with Er3+ and Yb3

Preparation from the aqueous alkoxide route of doped and co-doped lithium niobate nanocrystals with Er3+ and Yb3+ ions, and detailed investigations of their optical properties are presented in this comprehensive work. Simultaneous emission under femtosecond laser excitation of second harmonic generation (SHG) and up-conversion photoluminescence (UC-PL) is studied from colloidal suspensions according to the lanthanide ion contents. Special attention has been paid to produce phase pure nanocrystals of constant size (∼20 nm) thus allowing a straightforward comparison and optimization of the Er content for increasing the green UC-PL signals under 800 nm excitation. An optimal molar concentration at about 4 molar% in erbium ions is demonstrated, that is well above the concentration usually achieved in bulk crystals. Similarly, for co-doped LiNbO3 nanocrystals, different lanthanide concentrations and Yb/Er content ratios are tested allowing optimization of the green and red up-conversion excited at 980 nm, and analysis of the underlying mechanisms from excitation spectra. All together, these findings provide valuable insights into the wet-chemical synthesis and potential of doped and co-doped LiNbO3 nanocrystals for advanced applications, combining both SHG and UC-PL emissions from the particle core.

Magnetic-responsive upconversion luminescence resonance energy transfer (LRET) biosensor for ultrasensitive detection of SARS-CoV-2 spike protein

Upconversion nanoparticles (UCNPs) are ideal donors for luminescence resonance energy transfer (LRET)-based biosensors due to their excellent upconversion luminescence properties. However, the relatively large size of antibodies and proteins limits the application of UCNPs-based LRET biosensors in protein detection because the large steric hindrance of proteins leads to low energy transfer efficiency between UCNPs and receptors. Herein, we developed a magnetic responsive UCNPs-based LRET biosensor to control the coupling distance between antibody-functionalized UCNPs (Ab-UCNPs) as donors and antibody-PEG linker-magnetic gold nanoparticles (Ab-PEG-MGNs) as acceptors for ultrasensitive and highly selective detection of SARS-CoV-2 spike proteins. Our results showed that this platform reversibly shortened the coupling distance between UCNPs and MGNs and enhanced the LRET signal with a 10-fold increase in the limit of detection (LOD) from 20.6 pg/mL without magnetic modulation to 2.1 pg/mL with magnetic modulation within 1 h. The finite-difference time-domain (FDTD) simulation with cyclic distance change confirmed the distance-dependent LRET efficiency under magnetic modulation, which supported the experimental results. Moreover, the applications of this magnetic-responsive UCNP-based LRET biosensor could be extended to other large-size biomolecule detection.

Photophysics and its application in photon upconversion

Photoluminescence (PL) upconversion is a phenomenon involving light-matter interaction, where the energy of the emitted photons is higher than that of the incident photons. PL upconversion has promising applications in optoelectronic devices, displays, photovoltaics, imaging, diagnosis and treatment. In this review, we summarize the mechanism of PL upconversion and ultrafast PL physical processes. In particular, we highlight the advances in laser cooling, biological imaging, volumetric displays and photonics.

Ultrasensitive Colorimetric Luminescence Thermometry by Progressive Phase Transition

Luminescent materials that display quick spectral responses to thermal stimuli have attracted pervasive attention in sensing technologies. Herein, a programmable luminescence color switching in lanthanide-doped LiYO2 under thermal stimuli, based on deliberate control of the monoclinic (β) to tetragonal (α) phase transition in the crystal lattice, is reported. Specifically, a lanthanide-doping (Ln3+ ) approach to fine-tune the phase-transition temperature in a wide range from 294 to 359 K is developed. Accordingly, an array of Ln3+ -doped LiYO2 crystals that exhibit progressive phase transition, and thus sequential color switching at gradually increasing temperatures, is constructed. The tunable optical response to thermal stimuli is harnessed for colorimetric temperature indication and quantitative detection, demonstrating superior sensitivity and temperature resolution (Sr = 26.1% K-1 , δT = 0.008 K). The advances in controlling the phase-transition behavior of luminescent materials also offer exciting opportunities for high-performance personalized health monitoring.

Directive giant upconversion by supercritical bound states in the continuum

Photonic bound states in the continuum (BICs), embedded in the spectrum of free-space waves1,2 with diverging radiative quality factor, are topologically non-trivial dark modes in open-cavity resonators that have enabled important advances in photonics3,4. However, it is particularly challenging to achieve maximum near-field enhancement, as this requires matching radiative and non-radiative losses. Here we propose the concept of supercritical coupling, drawing inspiration from electromagnetically induced transparency in near-field coupled resonances close to the Friedrich-Wintgen condition2. Supercritical coupling occurs when the near-field coupling between dark and bright modes compensates for the negligible direct far-field coupling with the dark mode. This enables a quasi-BIC field to reach maximum enhancement imposed by non-radiative loss, even when the radiative quality factor is divergent. Our experimental design consists of a photonic-crystal nanoslab covered with upconversion nanoparticles. Near-field coupling is finely tuned at the nanostructure edge, in which a coherent upconversion luminescence enhanced by eight orders of magnitude is observed. The emission shows negligible divergence, narrow width at the microscale and controllable directivity through input focusing and polarization. This approach is relevant to various physical processes, with potential applications for light-source development, energy harvesting and photochemical catalysis.

Cross Relaxation Enables Spatiotemporal Color-Switchable Upconversion in a Single Sandwich Nanoparticle for Information Security

Smart control of ionic interaction dynamics offers new possibilities for tuning and editing luminescence properties of lanthanide-based materials. However, it remains a daunting challenge to achieve the dynamic control of cross relaxation mediated photon upconversion, and in particular the involved intrinsic photophysics is still unclear. Herein, this work reports a conceptual model to realize the color-switchable upconversion of Tm3+ through spatiotemporal control of cross relaxation in the design of NaYF4 :Gd@NaYbF4 :Tm@NaYF4 sandwich nanostructure. It shows that cross relaxation plays a key role in modulating upconversion dynamics and tuning emission colors of Tm3+ . Interestingly, it is found that there is a short temporal delay for the occurrence of cross relaxation in contrast to the spontaneous emission as a result of the slight energy mismatch between relevant energy levels. This further enables a fine emission color tuning upon non-steady state excitation. Moreover, a characteristic quenching time is proposed to describe the temporal evolution of cross relaxation quantitatively. These findings present a deep insight into the physics of ionic interactions in heavy doping systems, and also show great promise in frontier applications including information security, anti-counterfeiting and nanophotonics.

Novel Aspects about "Lifetime" in Upconversion Luminescence

Recent progress on the temporal response (TR) of lanthanide-doped upconversion luminescence (UCL) has enriched the means of UCL regulation, promoted advanced designs for customized applications such as biological diagnosis, high-capacity optical coding, and dynamic optical anti-counterfeiting, and pushed us to reacquaint the dynamic responses of sensitizer/activator ions in UCL systems. In particular, the lifetime of UCL should be revisited after discovery of novel experimental phenomena and luminescence mechanisms, i. e., it should be understood as the collective TR (in the decay edge) of all the involved ions rather than the reciprocal of the radiative rate of an individual ion. In this Concept, we retraced the latest understanding of the dynamics in UCL with special attention to the relationship between excitation and emission, means of TR regulation, and discussed existing challenges. It is expected to provide some fundamental insights to deepened understanding, further regulation, and frontier applications of TR features of UCL.

Excited-Multimer Mediated Supramolecular Upconversion on Multicomponent Lanthanide-Organic Assemblies

Upconversion (UC) is a fascinating anti-Stokes-like optical process with promising applications in diverse fields. However, known UC mechanisms are mainly based on direct energy transfer between metal ions, which constrains the designability and tunability of the structures and properties. Here, we synthesize two types of Ln8L12-type (Ln for lanthanide ion; L for organic ligand L1 or L2R/S) lanthanide-organic complexes with assembly induced excited-multimer states. The Yb8(L2R/S)12 assembly exhibits upconverted multimer green fluorescence under 980 nm excitation through a cooperative sensitization process. Furthermore, upconverted red emission from Eu3+ on the heterometallic (Yb/Eu)8L12 assemblies is also realized via excited-multimer mediated energy relay. Our findings demonstrate a new strategy for designing UC materials, which is crucial for exploiting photofunctions of multicomponent lanthanide-organic complexes.

Synthesis and Crystal Structure of the Europium(II) Hydride Oxide Iodide Eu5H2O2I4 Showing Blue-Green Luminescence

As the first europium(II) hydride oxide iodide, dark red single crystals of Eu5H2O2I4 could be synthesized from oxygen-contaminated mixtures of EuH2 and EuI2. Its orthorhombic crystal structure (a = 1636.97(9) pm, b = 1369.54(8) pm, c = 604.36(4) pm, Z = 4) was determined via single-crystal X-ray diffraction in the space group Cmcm. Anion-centred tetrahedra [HEu4]7+ and [OEu4]6+ serve as central building blocks interconnected via common edges to infinite ribbons parallel to the c axis. These ribbons consist of four trans-edge connected (Eu2+)4 tetrahedra as repetition unit, two H--centred ones in the inner part, and two O2--centred ones representing the outer sides. They are positively charged, according to ∞1{[Eu5H2O2]4+}, to become interconnected and charge-balanced by iodide anions. Upon excitation with UV light, the compound shows blue-green luminescence with the shortest Eu2+ emission wavelength ever observed for a hydride derivative, peaking at 463 nm. The magnetic susceptibility of Eu5H2O2I4 follows the Curie-Weiss law down to 100 K, and exhibits a ferromagnetic ordering transition at about 10 K.

Improving near-infrared luminescence in Er3+ doped CsPbBr3 quantum dots glasses through a certain energy transfer process

Er3+ has received extensive attention due to its excellent optical properties, especially its emission at 1535 nm in atmospheric propagation window. Enhancement and regulation of 1535 nm emission of Er3+ is of great significance to optical communication. In this work, growing of CsPbBr3 QDs has been controlled through adjusting annealing time which would precisely regulate conduction band of CsPbBr3 QDs to match energy levels of Er3+ enabling energy transfer between Er3+ and CsPbBr3 QDs. By steady-state and transient PL emission and excitation spectroscopy, we reveal multiple energy transfer processes between Er3+ and CsPbBr3 QDs under different excitation wavelengths in Er3+ doped CsPbBr3 QDs glass: under higher energy excitation (∼378 nm), energy transfer from Er3+ to CsPbBr3 QDs and this extra energy within CsPbBr3 QDs decay via a non-radiative pathway; under lower energy excitation (∼524 nm), energy transfer from conduction band of CsPbBr3 QDs to 4S3/2 energy level of Er3+ which significantly enhances PL emission of Er3+ in near infrared region (∼1535 nm, 4I13/2 → 4I15/2). These results provide a facile approach to enhance and regulate PL emission of Er3+ in near infrared region.

Highly hydrostable and flexible opal photonic crystal film for enhanced up-conversion fluorescence sensor of COVID-19 antibody

Efficient detection of related markers is significant for the early screening of COVID-19. Near infrared (NIR) light excited up-conversion fluorescence probes are ideal for biosensing but limited by the low luminescence efficiency. In this work, a novel highly stable opal photonic crystal (OPC) structure was designed to provide an OPC effect for up-conversion fluorescence enhancement, and sensitive Novel Coronavirus IgG up-conversion FRET-based sensor was further constructed. For the problems of water stability and mechanical stability of polymer OPC which cannot be solved for a long time, polymer spray combined with a flipped OPC film strategy is presented. Fragmented size OPC film was firmly fixed by polymer modification layer, which gave large size OPC film great water stability, mechanical stability and bending performance without affecting the fluorescence enhancement property. On this basis, the up-conversion emission intensity was enhanced significantly, and fluorescence resonant energy transfer (FRET) based Novel Coronavirus IgG antibody sensor was constructed. Monolayer up-conversion nanoparticles (UCNPs) on the surface of the polydopamine (PDA)/OPC film can make the fluorescent signal more sensitive, and effectively reduce the detection limit. The test device integrating NIR excitation and mobile phone realized the visual fast detection, showing remarkable sensing performance for COVID-19 antibodies with the limit of detection (LOD) of 0.1 ng mL-1. This detection platform will provide a more effective tool for early detection of the novel coronavirus.

Proof of crystal-field-perturbation-enhanced luminescence of lanthanide-doped nanocrystals through interstitial H+ doping

Crystal-field perturbation is theoretically the most direct and effective method of achieving highly efficient photoluminescence from trivalent lanthanide (Ln3+) ions through breaking the parity-forbidden nature of their 4f-transitions. However, exerting such crystal-field perturbation remains an arduous task even in well-developed Ln3+-doped luminescent nanocrystals (NCs). Herein, we report crystal-field perturbation through interstitial H+-doping in orthorhombic-phase NaMgF3:Ln3+ NCs and achieve a three-orders-of-magnitude emission amplification without a distinct lattice distortion. Mechanistic studies reveal that the interstitial H+ ions perturb the local charge density distribution, leading to anisotropic polarization of the F- ligand, which affects the highly symmetric Ln3+-substituted [MgF6]4- octahedral clusters. This effectively alleviates the parity-forbidden selective rule to enhance the 4f-4 f radiative transition rate of the Ln3+ emitter and is directly corroborated by the apparent shortening of the radiative recombination lifetime. The interstitially H+-doped NaMgF3:Yb/Er NCs are successfully used as bioimaging agents for real-time vascular imaging. These findings provide concrete evidence for crystal-field perturbation effects and promote the design of Ln3+-doped luminescent NCs with high brightness.

Recent advances in rare earth ion-doped upconversion nanomaterials: From design to their applications in food safety analysis

The misuse of chemicals in agricultural systems and food production leads to an increase in contaminants in food, which ultimately has adverse effects on human health. This situation has prompted a demand for sophisticated detection technologies with rapid and sensitive features, as concerns over food safety and quality have grown around the globe. The rare earth ion-doped upconversion nanoparticle (UCNP)-based sensor has emerged as an innovative and promising approach for detecting and analyzing food contaminants due to its superior photophysical properties, including low autofluorescence background, deep penetration of light, low toxicity, and minimal photodamage to the biological samples. The aim of this review was to discuss an outline of the applications of UCNPs to detect contaminants in food matrices, with particular attention on the determination of heavy metals, pesticides, pathogenic bacteria, mycotoxins, and antibiotics. The review briefly discusses the mechanism of upconversion (UC) luminescence, the synthesis, modification, functionality of UCNPs, as well as the detection principles for the design of UC biosensors. Furthermore, because current UCNP research on food safety detection is still at an early stage, this review identifies several bottlenecks that must be overcome in UCNPs and discusses the future prospects for its application in the field of food analysis.

Recent Progress in Photonic Upconversion Materials for Organic Lanthanide Complexes

Organic lanthanide complexes have garnered significant attention in various fields due to their intriguing energy transfer mechanism, enabling the upconversion (UC) of two or more low-energy photons into high-energy photons. In comparison to lanthanide-doped inorganic nanoparticles, organic UC complexes hold great promise for biological delivery applications due to their advantageous properties of controllable size and composition. This review aims to provide a summary of the fundamental concept and recent developments of organic lanthanide-based UC materials based on different mechanisms. Furthermore, we also detail recent applications in the fields of bioimaging and solar cells. The developments and forthcoming challenges in organic lanthanide-based UC offer readers valuable insights and opportunities to engage in further research endeavors.

Bodipy Dimer for Enhancing Triplet-Triplet Annihilation Upconversion Performance

Triplet-triplet annihilation upconversion (TTA-UC) has considerable potential for emerging applications in bioimaging, optogenetics, photoredox catalysis, solar energy harvesting, etc. Fluoroboron dipyrrole (Bodipy) dyes are an essential type of annihilator in TTA-UC. However, conventional Bodipy dyes generally have large molar extinction coefficients and small Stokes shifts (<20 nm), subjecting them to severe internal filtration effects at high concentrations, and resulting in low upconversion quantum efficiency of TTA-UC systems using Bodipy dyes as annihilators. In this study, a Bodipy dimer (B-2) with large Stokes shifts was synthesized using the strategy of dimerization of an already reported Bodipy annihilator (B-1). Photophysical characterization and theoretical chemical analysis showed that both B-1 and B-2 can couple with the red light-activated photosensitizer PdTPBP to fulfill TTA-UC; however, the higher fluorescence quantum yield of B-2 resulted in a higher upconversion efficiency (η_UC) for PdTPBP/B-2 (10.7%) than for PdTPBP/B-1 (4.0%). This study proposes a new strategy to expand Bodipy Stokes shifts and improve TTA-UC performance, which can facilitate the application of TTA-UC in photonics and biophotonics.

The Upconversion Luminescence of Ca3Sc2Si3O12:Yb3+,Er3+ and Its Application in Thermometry

To develop novel luminescent materials for optical temperature measurement, a series of Yb³⁺- and Er³⁺-doped Ca₃Sc₂Si₃O₁₂ (CSS) upconversion (UC) phosphors were synthesized by the sol-gel combustion method. The crystal structure, phase purity, and element distribution of the samples were characterized by powder X-ray diffraction and a transmission electron microscope (TEM). The detailed study of the photoluminescence emission spectra of the samples shows that the addition of Yb³⁺ can greatly enhance the emission of Er³⁺ by effective energy transfer. The prepared Yb³⁺ and Er³⁺ co-doped CSS phosphors exhibit green emission bands near 522 and 555 nm and red emission bands near 658 nm, which correspond to the ²H_11/2→⁴I_15/2, ⁴S_3/2→⁴I_15/2, and ⁴F_9/2→⁴I_15/2 transitions of Er³⁺, respectively. The temperature-dependent behavior of the CSS:0.2Yb³⁺,0.02Er³⁺ sample was carefully studied by the fluorescence intensity ratio (FIR) technique. The results indicate the excellent sensitivity of the sample, with a maximum absolute sensitivity of 0.67% K^-1 at 500 K and a relative sensitivity of 1.34% K^-1 at 300 K. We demonstrate here that the temperature measurement performance of FIR technology using the CSS:Yb³⁺,Er³⁺ phosphor is not inferior to that of infrared thermal imaging thermometers. Therefore, CSS:Yb³⁺,Er³⁺ phosphors have great potential applications in the field of optical thermometry.

Ultrasensitive detection of Staphylococcus aureus using a non-fluorescent cDNA-grafted dark BBQ®-650 chromophore integrated hydrophilic upconversion nanoparticles/aptamer system

A highly structured fluorometric bioassay has been proposed for screening Staphylococcus aureus (S. aureus). The study exploits (i) the spectral attributes of the hexagonal NaYF₄:Yb,Er upconversion nanoparticle (UCNP)-coated 3-aminopropyl)triethoxysilane; (ii) the intrinsic non-fluorescent quenching features of the highly stable dark blackberry (BBQ®-650) receptor; (iii) the aptamer (Apt-) biorecognition and binding affinity, and (iv) the complementary DNA hybridizer-linkage efficacy. The principle relied on the excited state energy transfer between the donor Apt-labeled NH₂-UCNPs at the 3' end, and cDNA-grafted BBQ®-650 at the 5' end, as the effective receptors. The donor moieties in proximity (< 10.0 nm) trigger hybridization with the cDNA-grafted dark BBQ®-650, as the receptors of energy from the ²F_5/2 level of Yb³⁺ ions to initiate the Förster resonance energy transfer pathway. This was confirmed by the decline in the excited-state lifetimes from 223.52 μs (τ₁) to 179.26 μs (τ₂). The existence of the target S. aureus in the bioassay attracts the Apt- resulting in the detachment of the acceptor, and disintegration of the complex configuration via conformation reversal. The re-activated fluorescence monitored at λex/em = 980/652 nm, as a function of the logarithmic concentration of S. aureus (42 to 4.2 × 10⁸ CFU mL^-1), yielded an ultra-low detection response of 2.0 CFU mL^-1. The bioassay screening of S. aureus in real samples revealed satisfactory recoveries (92.44-107.82%) and validation results (p > 0.05). Hence, the comprehensive Apt-labeled NH₂-UCNPs-cDNA-grafted dark BBQ®-650 bioassay offered fast and precise S. aureus screening in food and environmental settings.