808 nm Light-Triggered Thermometer-Heater Upconverting Platform Based on Nd3+-Sensitized Yolk-Shell GdOF@SiO2

Multi-effective nanoplatform with down/upconversion dual-mode emissions for NIR-II imaging and PDT/PTT synergistic therapy of early atherosclerosis

We design a multi-effective nanoplatform (CeO2:Nd@SiO2@CeO2:Yb,Er@SiO2-RB/MB/CD36) with down/upconversion dual-mode emissions and targeting ability in foam macrophages. Under NIR excitation, this nanoplatform can realize in vivo NIR-II imaging and PDT/PTT coordinated therapy for early AS simultaneously.

Transparent nanocrystal-in-glass composite fibers for multifunctional temperature and pressure sensing

The pursuit of compact and integrated devices has stimulated a growing demand for multifunctional sensors with rapid and accurate responses to various physical parameters, either separately or simultaneously. Fluorescent fiber sensors have the advantages of robust stability, light weight, and compact geometry, enabling real-time and noninvasive signal detection by monitoring the fluorescence parameters. Despite substantial progress in fluorescence sensors, achieving multifunctional sensing in a single optical fiber remains challenging. To solve this problem, in this study, we present a bottom-up strategy to design and fabricate thermally drawn multifunctional fiber sensors by incorporating functional nanocrystals with temperature and pressure fluorescence responses into a transparent glass matrix. To generate the desired nanocrystal-in-glass composite (NGC) fiber, the fluorescent activators, incorporated nanocrystals, glassy core materials, and cladding matrix are rationally designed. Utilizing the fluorescence intensity ratio technique, a self-calibrated fiber sensor is demonstrated, with a bi-functional response to temperature and pressure. For temperature sensing, the NGC fiber exhibits temperature-dependent near-infrared emission at temperatures up to 573 K with a maximum absolute sensitivity of 0.019 K-1. A pressure-dependent upconversion emission is also realized in the visible spectral region, with a linear slope of -0.065. The successful demonstration of multifunctional NGC fiber sensors provides an efficient pathway for new paradigms of multifunctional sensors as well as a versatile strategy for future hybrid fibers with novel combinations of magnetic, optical, and mechanical properties.

Near-Infrared-Responsive Rare Earth Nanoparticles for Optical Imaging and Wireless Phototherapy

Near-infrared (NIR) light is well-suited for the optical imaging and wireless phototherapy of malignant diseases because of its deep tissue penetration, low autofluorescence, weak tissue scattering, and non-invasiveness. Rare earth nanoparticles (RENPs) are promising NIR-responsive materials, owing to their excellent physical and chemical properties. The 4f electron subshell of lanthanides, the main group of rare earth elements, has rich energy-level structures. This facilitates broad-spectrum light-to-light conversion and the conversion of light to other forms of energy, such as thermal and chemical energies. In addition, the abundant loadable and modifiable sites on the surface offer favorable conditions for the functional expansion of RENPs. In this review, the authors systematically discuss the main processes and mechanisms underlying the response of RENPs to NIR light and summarize recent advances in their applications in optical imaging, photothermal therapy, photodynamic therapy, photoimmunotherapy, optogenetics, and light-responsive drug release. Finally, the challenges and opportunities for the application of RENPs in optical imaging and wireless phototherapy under NIR activation are considered.

Luminescence-Based Infrared Thermal Sensors: Comprehensive Insights

Recent chronological breakthroughs in materials innovation, their fabrication, and structural designs for disparate applications have paved transformational ways to subversively digitalize infrared (IR) thermal imaging sensors from traditional to smart. The noninvasive IR thermal imaging sensors are at the cutting edge of developments, exploiting the abilities of nanomaterials to acquire arbitrary, targeted, and tunable responses suitable for integration with host materials and devices, intimately disintegrate variegated signals from the target onto depiction without any discomfort, eliminating motional artifacts and collects precise physiological and physiochemical information in natural contexts. Highlighting several typical examples from recent literature, this review article summarizes an accessible, critical, and authoritative summary of an emerging class of advancement in the modalities of nano and micro-scale materials and devices, their fabrication designs and applications in infrared thermal sensors. Introduction is begun covering the importance of IR sensors, followed by a survey on sensing capabilities of various nano and micro structural materials, their design architects, and then culminating an overview of their diverse application swaths. The review concludes with a stimulating frontier debate on the opportunities, difficulties, and future approaches in the vibrant sector of infrared thermal imaging sensors.

Multifunctional Antibacterial Nanoplatform Bi2WO6:Nd3+/Yb3+/Er3+@MoS2 with Self-Monitoring Photothermal and Photodynamic Treatment

Synergistic therapy combining photothermal therapy and photodynamic therapy is considered to be a promising approach to treat cancer, but the precise temperature control of deep tissue remains a great challenge in achieving effective treatment. Herein, a two-dimensional Bi2WO6:Nd3+/Yb3+/Er3+@MoS2 nanoplatform with photothermal and photodynamic functions was constructed, where semiconductor MoS2 serves as both a photothermal agent and a photosensitizer. The photothermal conversion performance and the reactive oxygen species generation capacity of the nanoplatform were validated under the irradiation of 808 nm laser; meanwhile, the two sets of luminescence intensity ratios (IYb3+/INd3+ and IEr3+/INd3+) in the biological window region were selected as near-infrared temperature probes to monitor the heat generated during the photosynergistic process in real time. The feasibility of nanoplatform as an intratissue temperature probe and antibacterial agent was further assessed by vitro experiments, which provides an idea for designing multifunctional photosynergistic therapy nanoplatform.

Efficient Near-Infrared Response Antibacterial Ceramics Based on the Method of Facile In Situ Etching Upconversion Glass-Ceramics

As the world is faced with the coronavirus disease 2019 (COVID-19) pandemic, photocatalytic antibacterial ceramics can reduce the consumption of disinfectants and improve the safety of the public health environment. However, these antibacterial ceramics are often limited by poor stability and low light utilization efficiency. Herein, an antibacterial ceramic was developed via the method of facile in situ etching of upconversion glass-ceramics (UGC) (FIEG) with HCl, in which the BiOCl nanosheets were in situ grown on the surface of GC to improve its stability and antibacterial activity. The results suggest that the upconversion antibacterial ceramics can harvest and utilize near-infrared (NIR) photons efficiently, which display notable antibacterial activity for Escherichia coli (E. coli) under NIR (≥780 nm) and visible light (420-780 nm) irradiation, with a maximum inactivation rate of 7.5 log in 30 min. Meanwhile, in the cycle experiment, more than 6 log inactivation of E. coli was achieved using an antibacterial ceramic sheet after 2-h NIR light irradiation, and the stability of the antibacterial ceramic was discussed. Furthermore, the reactive species, fluorescence-based live/dead cells, and cell structure of bacteria were analyzed to verify the antibacterial mechanism. This study provides a promising strategy for the construction of efficient and stable antibacterial ceramics.

Optical heating and luminescence thermometry combined in a Cr3+-doped YAl3(BO3)4

The possibility of optical heating with simultaneous control of the generated light within a single phosphor is particularly attractive from the perspective of multiple applications. This motivates the search for new solutions to enable efficient optical heating. In response to these requirements, based on the high absorption cross-section of Cr³⁺ ions, the optical heater based on YAl₃(BO₃)₄:Cr³⁺ exhibiting highly efficient heating is developed. At the same time, the emission intensity ratio of ²E_(g) → ⁴A_2(g) and ⁴T_2(g) → ⁴A_2(g) of Cr³⁺ bands, thanks to the monotonic temperature dependence, enables remote temperature readout of the phosphor using luminescence thermometry technique. The combination of these two functionalities within a single phosphor makes YAl₃(BO₃)₄:Cr³⁺ a promising, self thermally controlled photothermal agent.

Ultrasensitive Pressure-Induced Optical Materials: Europium-Doped Hafnium Silicates with a Khibinskite Structure for Optical Pressure Sensors and WLEDs

Ultrasensitive pressure-induced optical materials are of great importance owing to their potential applications in optical pressure sensors. However, the lack of outstanding pressure sensitivity, observable color evolution, and structure reliability limits their further development in both practical applications and luminescence theory. To overcome the above problems, an enlightening methodology is proposed to explore the high sensitivity and phase stability of hafnium silicate K₂HfSi₂O₇ (KHSO) phosphor with a Khibinskite structure. By employing X-ray diffraction (XRD) Rietveld refinement, cryogenic spectroscopy, and ancillary calculations, information on Eu²⁺ ion occupation is completely obtained at atmospheric pressure. The remarkable pressure sensitivity (dλ/dP = 3.25 nm/GPa^-1) and excellent phase stability up to 20 GPa, along with the reproducible color hue variation, exhibit unprecedented superiority when used in optical pressure sensors. These advantages can be assigned to the pressure-induced Eu²⁺-selective occupation and the unique properties of 5d-4f transition (Stokes shift, nephelauxetic effect, and intense crystal field strength), which are clearly proved by measuring the XRD patterns, Raman spectra, and Gaussian fitting spectra under compression and decompression processes. The excellent luminescence property manifests that KHSO/Eu²⁺ can be considered as a potential luminescent material for solid-state lighting and optical pressure sensors.

Rare-Earth Doping in Nanostructured Inorganic Materials

Impurity doping is a promising method to impart new properties to various materials. Due to their unique optical, magnetic, and electrical properties, rare-earth ions have been extensively explored as active dopants in inorganic crystal lattices since the 18th century. Rare-earth doping can alter the crystallographic phase, morphology, and size, leading to tunable optical responses of doped nanomaterials. Moreover, rare-earth doping can control the ultimate electronic and catalytic performance of doped nanomaterials in a tunable and scalable manner, enabling significant improvements in energy harvesting and conversion. A better understanding of the critical role of rare-earth doping is a prerequisite for the development of an extensive repertoire of functional nanomaterials for practical applications. In this review, we highlight recent advances in rare-earth doping in inorganic nanomaterials and the associated applications in many fields. This review covers the key criteria for rare-earth doping, including basic electronic structures, lattice environments, and doping strategies, as well as fundamental design principles that enhance the electrical, optical, catalytic, and magnetic properties of the material. We also discuss future research directions and challenges in controlling rare-earth doping for new applications.

Advances in Hollow Inorganic Nanomedicines for Photothermal-Based Therapies

Nanotechnology has prompted the development of hollow inorganic nanomedicine. These medicines are now widely investigated as photothermal-based therapies for various diseases due to their high loading capacity, tuneable wavelength, relatively small size and low density. We begin this review with a brief introduction, followed by a summary of the development of imaging-guided photothermal therapy (PTT) for cancer treatment during the last three years (from 2017 to 2020). We then introduce the antibacterial effects of these medicines on some bacterial infections, in which the pathogenic bacteria can be killed by mild photothermal effects, ions and antibiotic release. Other diseases can also be treated using hollow inorganic photothermal agents. Specifically, we discuss the use of PTT for treating Alzheimer's disease, obesity and endometriosis. Finally, we share our perspectives on the current challenges and future prospects of using hollow inorganic materials in clinical PTT for various diseases.

Upconversion luminescence and temperature sensing properties of NaGd(WO4)2:Yb3+/Er3+@SiO2 core-shell nanoparticles

Optical thermometry based on the fluorescence intensity ratio (FIR) of two thermally coupled levels in lanthanide ions has potential application in non-contact optical temperature sensing techniques. In this work, a shell of SiO2 with tunable thickness was uniformly coated on NaGd(WO4)2:Yb3+/Er3+ core upconversion nanoparticles (UCNPs). The effects of the silica shell on UC luminescence and thermal sensing properties of core-shell NaGd(WO4)2:Yb3+/Er3+@SiO2 UCNPs were investigated. Under 980 nm laser excitation, the temperature-dependent UC emission spectra of obtained samples were measured. The FIR was analyzed based on the thermally coupled 2H11/2 and 4S3/2 levels of Er3+ in the biological temperature range of 300-350 K, in which the Boltzmann distribution is applied. The emission from the upper 2H11/2 state within Er3+ was enhanced as temperature increased due to the thermal effect. Absolute sensitivities (S A) and relative sensitivities (S R) of the core and core-shell UCNPs were calculated. It was found that after SiO2 coating, the maximum S A was enhanced by ∼2-fold (1.03% K-1 at 350 K). Especially, S A was as high as 2.14% K-1 at 350 K by analyzing the FIR of the non-thermally coupled 2H11/2 and 4F9/2 levels.

NIR Luminescence Enhancement of YVO4:Nd Phosphor for Biological Application

This work reports two systematic studies related to yttrium vanadate (YVO4) phosphors. The first evaluates how the annealing temperature and V5+/Y3+ molar ratio determine the emergence of a single YVO4 tetragonal phase, whereas the second concerns the optimal Nd3+ concentration to improve the infrared emission properties for bio-labelling applications. The YVO4:Nd phosphors were synthesized by adapting the non-hydrolytic sol-gel route. For the first study, samples containing different V5+/Y3+ molar ratios (1.02, 1.48, 1.71, or 3.13) were obtained. For the second study, YVO4:Nd phosphors containing different Nd3+ concentrations (1.0, 3.0, 5.0, or 10.0% in mol) were prepared. X-ray diffractometry and RAMAN spectroscopy results revealed that, regardless of the heat-treatment temperature, the V5+/Y3+ molar ratio of 1.48 was the best composition to avoid undesired phases like Y2O3 and V2O5. Photoluminescence results indicated that the sample containing 3.0% in mol of Nd3+ and annealed at 1000 °C presented the best infrared emission properties. This sample displayed an intense broad band in the ultraviolet region, which was ascribed to the VO43- charge transfer band, as well as several bands in the visible and infrared regions, which were attributed to the Nd3+ intraconfigurational f-f transitions. Regardless of the excitation wavelength (ultraviolet, visible, or near-infrared), the mean radiative lifetime was about 12.00 µs. The prepared phosphors presented absorption and emission bands in the biological window (BW) regions, which are located between 750 and 900 nm and between 1000 and 1300 nm, so they are candidates for applications in medical imaging and diagnoses.

Temperature Feedback-Controlled Photothermal/Photodynamic/Chemodynamic Combination Cancer Therapy Based on NaGdF4 :Er,Yb@NaGdF4 :Nd@Cu-BIF Nanoassemblies

The intelligent design of multifunctional nanoplatforms is critical for cancer therapy. Herein, NaGdF₄ :Er,Yb@NaGdF₄ :Nd@Cu(II) boron-imidazolate frameworks (denoted as CSNPs@Cu-BIF) nanoassemblies are designed and fabricated. Upon a single 808 nm laser irradiation, the nanoassemblies not only show the outstanding photothermal conversion capacity (η = 41.7%) but also generate cytotoxic reactive oxygen species through an in situ Fenton-like reaction and fluorescence resonance energy transfer. Importantly, the nanoassemblies simultaneously introduce remarkable antitumor efficacy via photothermal/photodynamic/chemodynamic combination therapy both in vitro and in vivo. To improve the therapeutic effect of solid tumor ablation, it is highly desirable to monitor the treatment process in real-time. Multiclinical imaging modalities of ultrasonography are employed to systematically investigate the ablation mechanism of solid tumors in vivo. Furthermore, the significant difference between the eigen temperature of CSNPs@Cu-BIF nanoassemblies obtained by the temperature-sensitive emission bands signal changes and the apparent temperature recorded by the thermal imaging camera is 14.55 K at equilibrium. This current work therefore supplies an alternative strategy in temperature feedback-controlled accurate cancer therapy.

Advances and challenges for fluorescence nanothermometry

Fluorescent nanothermometers can probe changes in local temperature in living cells and in vivo and reveal fundamental insights into biological properties. This field has attracted global efforts in developing both temperature-responsive materials and detection procedures to achieve sub-degree temperature resolution in biosystems. Recent generations of nanothermometers show superior performance to earlier ones and also offer multifunctionality, enabling state-of-the-art functional imaging with improved spatial, temporal and temperature resolutions for monitoring the metabolism of intracellular organelles and internal organs. Although progress in this field has been rapid, it has not been without controversy, as recent studies have shown possible biased sensing during fluorescence-based detection. Here, we introduce the design principles and advances in fluorescence nanothermometry, highlight application achievements, discuss scenarios that may lead to biased sensing, analyze the challenges ahead in terms of both fundamental issues and practical implementations, and point to new directions for improving this interdisciplinary field.

Lanthanide Upconverted Luminescence for Simultaneous Contactless Optical Thermometry and Manometry-Sensing under Extreme Conditions of Pressure and Temperature

The growing interest in the miniaturization of various devices and conducting experiments under extreme conditions of pressure and temperature causes the need for the development of small, contactless, precise, and accurate optical sensors without any electrical connections. In this work, YF₃:Yb³⁺-Er³⁺ upconverting microparticles are used as a bifunctional luminescence sensor for simultaneous temperature and pressure measurements. Different changes in the properties of Er³⁺ green and red upconverted luminescence, after excitation of Yb³⁺ ions in the near-infrared at ∼975 nm, are used to calibrate pressure and/or temperature inside the hydrostatic chamber of a diamond anvil cell (DAC). For temperature sensing, changes in the relative intensities of the Er³⁺ green upconverted luminescence of ²H_11/2 and ⁴S_3/2 thermally coupled multiplets to the ⁴I_15/2 ground state, whose relative populations follow a Boltzmann distribution, are calibrated. For pressure sensing, the spectral shift of the Er³⁺ upconverted red emission peak at ∼665 nm, between the Stark sublevels of the ⁴F_9/2 → ⁴I_15/2 transition, is used. Experiments performed under simultaneous extreme conditions of pressure, up to ∼8 GPa, and temperature, up to ∼473 K, confirm the possibility of remote optical pressure and temperature sensing.

Robust liquid-core nanocapsules as biocompatible and precise ratiometric fluorescent thermometers for living cells

Intracellular thermometry with favorable biocompatibility and precision is essential for insight into temperature-related cellular events. Here, liquid-core nanocapsule ratiometric fluorescent thermometers (LCN-RFTs) were prepared by encapsulating thermosensitive organic fluorophores (N,N'-di(2-ethylhexyl)-3,4,9,10-perylene tetracarboxylic diimide, DEH-PDI) with hydrophobic solvent (2,2,4-trimethylpentane, TMP) into polystyrene/silica hybrid nanoshells. As the fluorescent thermosensitive unit of the LCN-RFT, the TMP solution of DEH-PDI was responsible for the fluorescence response to temperature. Benefitting from the hydrophilic nanoshells, the LCN-RFTs exhibited favorable anti-interference and biocompatibility. Furthermore, the LCN-RFTs showed an excellent precision of 0.02 °C-0.10 °C in a simulated physiological environment from 10.00 °C to 90.00 °C, and were employed to realize intracellular thermometry with an outstanding precision of 0.06 °C-0.14 °C. This work provides a feasible method of using hydrophobic organic fluorophores for intracellular thermometry by encapsulating them into nanocapsules.

Liposomal nanotheranostics for multimode targeted in vivo bioimaging and near-infrared light mediated cancer therapy

Developing a nanotheranostic agent with better image resolution and high accumulation into solid tumor microenvironment is a challenging task. Herein, we established a light mediated phototriggered strategy for enhanced tumor accumulation of nanohybrids. A multifunctional liposome based nanotheranostics loaded with gold nanoparticles (AuNPs) and emissive graphene quantum dots (GQDs) were engineered named as NFGL. Further, doxorubicin hydrochloride was encapsulated in NFGL to exhibit phototriggered chemotherapy and functionalized with folic acid targeting ligands. Encapsulated agents showed imaging bimodality for in vivo tumor diagnosis due to their high contrast and emissive nature. Targeted NFGL nanohybrids demonstrated near infrared light (NIR, 750 nm) mediated tumor reduction because of generated heat and Reactive Oxygen Species (ROS). Moreover, NFGL nanohybrids exhibited remarkable ROS scavenging ability as compared to GQDs loaded liposomes validated by antitumor study. Hence, this approach and engineered system could open new direction for targeted imaging and cancer therapy.

Luminescent properties and ratiometric optical thermometry of Ln-BDC-F4 compounds

A series of luminescent lanthanide compounds with 2, 3, 5, 6-tetrafluoro-1, 4-benzenedicarboxylate (H₂BDC-F₄) acting as the organic ligand have been synthesized by solvothermal reaction. The terbium compound (C1: Tb-BDC-F₄) and europium compound (C7: Eu-BDC-F₄) exhibit intense green and red luminescence respectively upon excitation of the ligand at room temperature, which suggests that H₂BDC-F₄ ligand can sensitize Tb³⁺ and Eu³⁺ ions effectively. The emitting color of the mixed lanthanide compounds is tunable from green to red in the mixed lanthanide compounds Tb_xEu_1-x-BDC-F₄ (x = 0.3%, 0.5%, 0.7%, 1%, and 2%), which is caused by energy transfer from Tb³⁺ to Eu³⁺. The self-reference ratiometric optical thermometry was realized by fluorescence intensity ratio between Tb³⁺ green emission (∼544 nm) and Eu³⁺red emission (∼ 619 nm). The maximum relative sensitivity S_R,max is 0.76%K^-1@50 K. Furthermore, the emitting color of C5: Eu_0.01Tb_0.99-BDC-F₄ could be tuned from green to orange by temperature in the range of 50 to 300 K. It allows the mixed Eu/Tb-BDC-F₄ compounds to be potentially used as sensitive luminescent materials to directly imagine the temperature distribution.

Thermal monitoring during photothermia: hybrid probes for simultaneous plasmonic heating and near-infrared optical nanothermometry

The control of temperature during photothermal therapy is key to preventing unwanted damage in surrounding tissue or post-treatment inflammatory responses. Lack of accurate thermal control is indeed one of the main limitations that hyperthermia techniques present to allow their translation into therapeutic applications. We developed a nanoprobe that allows controlled local heating, combined with in situ nanothermometry. The design of the probe follows a practical rationale that aims at simplifying experimental requirements and exploits exclusively optical wavelengths matching the first and second biological windows in the near-infrared. Methods: Hybrid nanostructures were chemically synthesized, and combine gold nanostars (photothermal agents) with CaF₂:Nd³⁺,Y³⁺ nanoparticles (luminescent nanothermometers). Both components were simultaneously excited in the near-infrared range, at 808 nm. Following the goal of simplifying the thermal monitoring technique, the luminescent signal was recorded with a portable near-infrared detector. The performance of the probes was tested in 3D tumor spheroids from a human glioblastoma (U87MG) cell line. The location of the beads within the spheroids was determined measuring Nd³⁺ emission in a commercial Lightsheet microscope, modified in-house to be able to select the required near-infrared wavelengths. The temperature achieved inside the tumor spheroids was deduced from the luminescence of Nd³⁺, following a protocol that we developed to provide reliable thermal readings. Results: The choice of materials was shown to work as an optically excited hybrid probe. Depending on the illumination parameters, temperature can be controlled in a range between 37 ºC and 100 ºC. The near-infrared emission of nanothermometers also allows microscopic tracking of the hybrid nanostructures, confirming that the probes can penetrate deeper into the spheroid mass. We observed that, application of optical thermometry in biological environments requires often neglected considerations, since the optical signal changes along the optical path. Accordingly, we developed data analysis protocols that guarantee reliable thermal readings. Conclusions: The prepared hybrid probes are internalized in 3D tumor spheroids and can be used to induce cell death through photothermal effects, while simultaneously measuring the local temperature in situ. We show that luminescent thermometry in biomedical applications requires the development of protocols that guarantee accurate readings. Regarding photothermal treatments, we observe a sharp thermal threshold at around 55 ºC (for 10 min treatments) that separates high survival ratio from complete cell death.

Upconverting Lanthanide Fluoride Core@Shell Nanorods for Luminescent Thermometry in the First and Second Biological Windows: β-NaYF4:Yb3+- Er3+@SiO2 Temperature Sensor

Upconverting core@shell type β-NaYF₄:Yb³⁺-Er³⁺@SiO₂ nanorods have been obtained by a two-step synthesis process, which encompasses hydrothermal and microemulsion routes. The synthesized nanomaterial forms stable aqueous colloids and exhibits a bright dual-center emission (λ_ex = 975 nm), i.e., upconversion luminescence of Er³⁺ and down-shifting emission of Yb³⁺, located in the first (I-BW) and the second (II-BW) biological windows of the spectral range, respectively. The intensity ratios of the emission bands of Er³⁺ and Yb³⁺ observed in the vis-near-infrared (NIR) range monotonously change with temperature, i.e., the thermalized Er³⁺ levels (²H_11/2 → ⁴I_15/2/⁴S_3/2 → ⁴I_15/2) and the nonthermally coupled Yb³⁺/Er³⁺ levels (²F_5/2 → ²F_7/2/⁴I_9/2 → ⁴I_15/2 or ⁴F_9/2 → ⁴I_15/2). Hence, their thermal evolutions have been correlated with temperature using the Boltzmann type distribution and second-order polynomial fits for temperature-sensing purposes, i.e., Er³⁺ 525/545 nm (max S_r = 1.31% K^-1) and Yb³⁺/Er³⁺ 1010/810 nm (1.64% K^-1) or 1010/660 nm (0.96% K^-1). Additionally, a fresh chicken breast was used as a tissue imitation in the performed ex vivo experiment, showing the advantage of the use of NIR Yb³⁺/Er³⁺ bands, vs. the typically used Er³⁺ 525/545 nm band ratio, i.e., better penetration of the luminescence signal through the tissue in the I-BW and II-BW. Such nanomaterials can be utilized as accurate and effective, broad-range vis-NIR optical, contactless sensors of temperature.

Stepwise Ligand-induced Self-assembly for Facile Fabrication of Nanodiamond-Gold Nanoparticle Dimers via Noncovalent Biotin-Streptavidin Interactions

Nanodiamond-gold nanoparticle (ND-AuNP) dimers constitute a potent tool for controlled thermal heating of biological systems on the nanoscale, by combining a local light-induced heat source with a sensitive local thermometer. Unfortunately, previous solution-based strategies to build ND-AuNP conjugates resulted in large nanoclusters or a broad population of multimers with limited separation efficiency. Here, we describe a new strategy to synthesize discrete ND-AuNP dimers via the synthesis of biotin-labeled DNA-AuNPs through thiol chemistry and its immobilization onto the magnetic bead (MB) surface, followed by reacting with streptavidin-labeled NDs. The dimers can be easily released from MB via a strand displacement reaction and separated magnetically. Our method is facile, convenient, and scalable, ensuring high-throughput formation of very stable dimer structures. This ligand-induced self-assembly approach enables the preparation of a wide variety of dimers of designated sizes and compositions, thus opening up the possibility that they can be deployed in many biological actuation and sensing applications.

Optical Pressure Sensor Based on the Emission and Excitation Band Width (fwhm) and Luminescence Shift of Ce3+-Doped Fluorapatite-High-Pressure Sensing

A novel, contactless optical sensor of pressure based on the luminescence red-shift and bandwidth (full width at half-maximum, fwhm) of the Ce³⁺-doped fluorapatite-Y₆Ba₄(SiO₄)₆F₂ powder has been successfully synthesized via a facile solid-state method. The obtained material exhibits a bright blue emission under UV light excitation. It was characterized using powder X-ray diffraction, scanning electron microscopy and luminescence spectroscopy, including high-pressure measurements of excitation and emission spectra, up to above ∼30 GPa. Compression of the material resulted in a significant red-shift of the allowed 4f → 5d and 5d → 4f transitions of Ce³⁺ in the excitation and emission spectra, respectively. The pressure-induced monotonic shift of the emission band, as well as changes in the excitation/emission band widths, have been correlated with pressure for sensing purposes. The material exhibits a high pressure sensitivity (dλ/d P ≈ 0.63 nm/GPa) and outstanding signal intensity at high-pressure conditions (∼90% of the initial intensity at around 20 GPa) with minimal pressure-induced quenching of luminescence.

Switchable up-conversion luminescence bioimaging and targeted photothermal ablation in one core–shell-structured nanohybrid by alternating near-infrared light

Upon NIR irradiation, a GdOF:Yb/Er@(GNRs@BSA)-FA nanohybrid was expected to be a potential multifunctional imaging tracer and photothermal ablation agent switched controllably for cancer theranostics.

Enhancing the antibacterial efficacy of low-dose gentamicin with 5 minute assistance of photothermy at 50 °C

Implant materials are prone to bacterial infections and cause serious consequences, while traditional antibiotic therapy has a long treatment cycle and even causes bacterial resistance.

In situ construction of the BiOCl/Bi2Ti2O7 heterojunction with enhanced visible-light photocatalytic activity

Herein, a BiOCl/Bi₂Ti₂O₇ heterojunction was prepared as an efficient visible light-driven photocatalyst through an in situ hydrothermal method, and its photocatalytic properties were investigated via a comparable method.

Upconverting LuVO4:Nd3+/Yb3+/Er3+@SiO2@Cu2S Hollow Nanoplatforms for Self-monitored Photothermal Ablation

Self-monitored photothermal therapy (PTT) with minimal collateral damages has emerged as a challenging strategy for antibacterial and cancer treatments, which could be fulfilled via the rational integration of luminescent thermometry and photothermal ablation within a single upconverting (UC) nanoplatform. Herein, 808 nm light-driven dual-functional nanoplatforms LuVO₄:Nd³⁺/Yb³⁺/Er³⁺@SiO₂@Cu₂S were successfully developed using olivelike LuVO₄:Nd³⁺/Yb³⁺/Er³⁺ hollow nanoparticles as the thermal-sensing core and ultrasmall Cu₂S nanoparticles as the photothermal satellite. Irradiated by 808 nm laser, thermal-sensing behaviors of samples were evaluated based on the high-purity Er³⁺ green emissions, while the surface-attached Cu₂S exhibited superior photothermal effects due to the efficient absorption of incident laser and near-infrared emissions from the luminescent core. The feasibility of bifunctional samples acting as self-monitored photothermal agents in subtissues and antibacterial agents against drug-resistant bacteria was separately assessed. Results provide deeper insights into the desirable design of 808 nm-driven multifunctional nanoplatforms with intense UC emission, sensitive thermometry, and effective photothermal conversion toward self-monitored PTT with high therapeutic accuracy.

Apparent self-heating of individual upconverting nanoparticle thermometers

Individual luminescent nanoparticles enable thermometry with sub-diffraction limited spatial resolution, but potential self-heating effects from high single-particle excitation intensities remain largely uninvestigated because thermal models predict negligible self-heating. Here, we report that the common "ratiometric" thermometry signal of individual NaYF4:Yb3+,Er3+ nanoparticles unexpectedly increases with excitation intensity, implying a temperature rise over 50 K if interpreted as thermal. Luminescence lifetime thermometry, which we demonstrate for the first time using individual NaYF4:Yb3+,Er3+ nanoparticles, indicates a similar temperature rise. To resolve this apparent contradiction between model and experiment, we systematically vary the nanoparticle's thermal environment: the substrate thermal conductivity, nanoparticle-substrate contact resistance, and nanoparticle size. The apparent self-heating remains unchanged, demonstrating that this effect is an artifact, not a real temperature rise. Using rate equation modeling, we show that this artifact results from increased radiative and non-radiative relaxation from higher-lying Er3+ energy levels. This study has important implications for single-particle thermometry.

Spectroscopic properties of LaGaO3:V,Nd3+ nanocrystals as a potential luminescent thermometer

In this work we present the spectroscopic properties of LaGaO3:V,Nd3+ nanocrystals, which have been successfully obtained by the Pechini method. This is the first study where vanadium ions were applied in a LaGaO3 lattice for a non-contact luminescent thermometer. It was found that vanadium ions in the LaGaO3 matrix appear in three oxidation states, namely V5+, V4+ and V3+. It was found that the relative emission intensities of various states of vanadium ions depend strongly on grain size and therefore the emission color of LaGaO3:V can be easily modulated via the annealing temperature. The spectroscopic properties of this material were investigated in a wide temperature range (-150-300 °C). It was found that in the case of V-singly doped nanocrystals, the V4+ ions, reveal the best temperature sensing performance with high relative sensitivity (S = 1.76% °C-1) and broad usable temperature range (-50-150 °C). The different rates of thermal luminescence quenching of the vanadium ions provide three forms of non-contact temperature sensor, namely LaGaO3:V5+,Nd3+, LaGaO3:V4+,Nd3+ and LaGaO3:V3+,Nd3+. The highest sensitivities were found to be 1% °C-1 (at -5 °C and 90 °C), 0.49% °C-1 (at -20 °C) and 1.44% °C-1 (at 75 °C) for LaGaO3:V5+,Nd3+, LaGaO3:V4+,Nd3+ and LaGaO3:V3+,Nd3+, respectively.

Local symmetric distortion boosted photon up-conversion and thermometric sensitivity in lanthanum oxide nanospheres

It is essential to simultaneously boost the luminescence intensity and thermometric sensitivity of up-converted optical thermometers towards potential biomedical sensing applications. Herein, the effects of local site symmetry on the up-conversion (UC) emission and thermal sensing ability in trigonal-phased La2O3:Er3+/Yb3+ nanospheres were qualitatively explored using cubic-phased Lu2O3 and Y2O3 with a similar shape and phonon energy as contrasts. Under 980 nm light excitation, much stronger UC emissions were detected in La2O3 samples than that in cubic Lu2O3 and Y2O3 samples, and the possible mechanisms were elaborately proposed using Eu3+ as a luminescent probe. Thermo-responsive emission intensity from 2H11/2/4S3/2 levels was monitored to evaluate the absolute sensitivity of three samples, which strongly depends on the dopant-induced local site symmetric distortions according to the Judd-Ofelt theory. The potentiality of La2O3:Er3+/Yb3+ for sub-tissue thermometry was also validated by ex vivo experiments. Results open a promising avenue for realizing highly sensitive thermometry with a large signal-to-noise ratio in sub-tissues via finely tailoring the local site symmetry.

NIR-to-NIR Deep Penetrating Nanoplatforms Y2O3:Nd3+/Yb3+@SiO2@Cu2S toward Highly Efficient Photothermal Ablation

A difunctional nano-photothermal therapy (PTT) platform with near-infrared excitation to near-infrared emission (NIR-to-NIR) was constructed through core-shell structures Y₂O₃:Nd³⁺/Yb³⁺@SiO₂@Cu₂S (YRSC), in which the core Y₂O₃:Nd³⁺/Yb³⁺ and shell Cu₂S play the role of bioimaging and photothermal conversion function, respectively. The structure and composition of the present PTT agents (PTAs) were characterized by powder X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectra. The NIR emissions of samples in the biological window area were measured by photoluminescence spectra under the excitation of 808 nm laser; further, the penetration depth of NIR emission at different wavelengths in biological tissue was also demonstrated by comparing with visible (vis) emission from Y₂O₃:Yb³⁺/Er³⁺@SiO₂@Cu₂S and NIR emission from YRSC through different injection depths in pork muscle tissues. The photo-thermal conversion effects were achieved through the outer ultrasmall Cu₂S nanoparticles simultaneously absorb NIR light emission from the core Y₂O₃:Nd^3+/Yb³⁺ and the 808 nm excitation source to generate heat. Further, the heating effect of YRSC nanoparticles was confirmed by thermal imaging and ablation of YRSC to Escherichia coli and human hepatoma (HepG-2) cells. Results indicate that the YRSC has potential applications in PTT and NIR imaging in biological tissue.

Real-time detection of the nanoparticle induced phytotoxicity in rice root tip through the visible red emissions of Eu3+ ions

Phytotoxicity is one of the most important factors involved in the reduction of crop production. With the introduction of NaBiF4 nanoparticles, the effect of the particle size (>50 nm) on rice development was systematically studied. Through the exogenous treatment of multiple concentrations of nanoparticles, the primary root length, lateral root number, and lateral root length were significantly inhibited under higher content of nanoparticles, but more crown root formation was induced, which might be due to phytotoxicity. With the help of the red emission of the Eu3+-activated NaBiF4 nanoparticles, we could infer that the nanoparticles were accumulated in the root tip cells in the division and elongation zone but not in the mature region. Additionally, the investigation on the influence of the studied nanoparticles on the gene level and the expression of phytotoxicity related genes was performed to further identify the effect of the nanoparticles on the rice root development. These results potentially explain the effect of larger nanoparticles on phytotoxicity in the plant roots.

Highly uniform and monodisperse β-NaYF4 : Sm3+ nanoparticles for a nanoscale optical thermometer

Monodisperse β-NaYF₄:1%Sm³⁺ nanoparticles were fabricated successfully via the thermal decomposition technique. Strong temperature dependence of the Sm³⁺ emission was observed when its thermally populated state H_7/26 was directly excited to the G_5/24 level. This strategy not only can eliminate laser heating and background Stokes-type scattering noise but also has a high quantum yield as a result of one-photon excitation process. Under 594.0 nm laser excitation, the emission intensity of G_5/24-H_5/26 enhances monotonously with rising temperature from 300 K to 430 K, including a physiological temperature range (27°C-60°C). The relative temperature sensitivity can reach 1.1%   K^-1 and 0.91%  K^-1 at 300 K and 330 K, respectively. In addition, the repeatability of temperature sensing was evaluated under several heating-cooling cycles, and the decay curves of the emission at 560.0 nm (G_5/24-H_5/26) at different temperatures were also investigated. These results raise the prospects of monodisperse β-NaYF₄:1%Sm³⁺ nanoparticles for optical temperature sensing in biomedicine fields.

Synthesis and luminescence properties of Eu3+-activated BiF3 nanoparticles for optical thermometry and fluorescence imaging in rice root

The luminescence, optical thermometric properties, phytotoxicity, and fluorescence imaging in plant cells of Eu³⁺-activated BiF₃ nanoparticles were systematically studied. Under the excitation of near-ultraviolet light, the prepared compounds emitted visible red light arising from the intra-4f transitions of Eu³⁺ ions. By employing the fluorescence intensity ratio technique, the temperature sensing performance of the synthesized nanoparticles was investigated and the maximum sensitivity was demonstrated to be 3.4 × 10⁻⁵ K⁻¹ at 443 K. Furthermore, the rice root, which was treated with Eu³⁺-activated BiF₃ nanoparticles, showed similar primary root elongation and crown root number to the seedlings cultivated in the MS0 medium without nanoparticles, indicating the relatively low phytotoxicity of the resultant samples to the rice root. Additionally, the results of the toxicity-related gene levels and phenotypes also demonstrated the low phytotoxicity of the as-prepared nanoparticles to the plant cells. Ultimately, with the help of the red emission of Eu³⁺ ions, the studied compounds were found to be accumulated in the division and differentiation regions of the rice root rather than transferred to the above-ground tissues. These results suggest that the Eu³⁺-activated BiF₃ nanoparticles may have potential applications in non-invasive optical temperature sensors and fluorescence probes in plant cells.

The luminescence, optical thermometric properties, phytotoxicity, and fluorescence imaging in plant cells of Eu³⁺-activated BiF₃ nanoparticles were systematically studied.

Investigation of photoluminescence properties, Judd–Ofelt analysis, luminescence nanothermometry and optical heating behaviour of Er3+/Eu3+/Yb3+:NaZnPO4 nanophosphors

The Er³⁺/Eu³⁺/Yb³⁺:NaZnPO₄ nanophosphors can be used as temperature sensors and optical nano-heaters with significant sensor sensitivity.

808 nm-triggered optical thermometry based on up-conversion luminescence of Nd3+/Yb3+/Er3+ doped MIn2O4 (M = Ca, Sr and Ba) phosphors

808 nm driven UCL mechanism and intrinsic structure-dependent optical thermometric performance of MIn₂O₄:Nd³⁺/Yb³⁺/Er³⁺ (M = Ca, Sr, and Ba) are elucidated.