Zero Phonon Line and Near-Infrared Luminescence in Cs4CdSb2-xCrxCl12 Quadruple-Layered Halide Double Perovskite

There is growing interest in understanding the optoelectronic properties of inorganic lead-free layered halide double perovskites (LHDPs). Here, we report a distinctive sharp zero phonon line (ZPL) emission at 727 nm and an intense, broad near-infrared (NIR) emission at 757 nm from the photoluminescence (PL) spectra measured at temperatures below 217 K, resulting from Cr3+ substitution in Cs4CdSb2Cl12 LHDPs. Pristine Cs4CdSb2Cl12 exhibits only a weak and broad self-trapped excitonic emission centered around 590 nm. On the contrary, an NIR emission (fwhm = 72.5 nm) at 757 nm is also observed at 300 K in Cs4CdSb2-xCrxCl12 (x = 0.05 to 0.3) originating from the d-d transition of Cr3+ ions. This broad mode evolves into 2 distinct emissions: a ZPL (at 727 nm) and an intense, broad NIR (at 746 nm) sideband below 217 K. The ZPL originates from the spin-allowed 4T2g → 4A2g d-d transition from Cr3+. ZPL intensity increases with Cr3+ substitution. This study demonstrates the promising optical properties of Cr3+-substituted LHDPs, indicating their potential for future applications in optoelectronic devices.

Tunable NIR Emission of Cr3+-Activated Double-Perovskite Tantalates and Improvement of Luminescence Properties via Codoping Yb3

Broadband near-infrared (NIR) luminescent materials exhibit great potential in many fields including nondestructive examination, biological imaging, and night vision. Herein, the tunable NIR emission can be realized based on Sr2MTaO6:Cr3+ (M = Ga, Sc, In) tantalate phosphors with a double-perovskite structure, with the emission peak varying from 782 to 880 nm via cation modulation. Specifically, after being stimulated by a 460 nm blue light, the Sr2GaTaO6/Cr3+ phosphor demonstrates a broadband NIR emission with the full width at half-maximum (fwhm) over 180 nm, originating from two octahedral sites of Ga3+ and Ta5+ in Sr2GaTaO6 that can be occupied by Cr3+ ions. By using the Yb3+ codoping strategy, the efficient energy transfer process (Cr3+ → Yb3+) enables remarkable expansion of the fwhm to 304 nm and significant improvement in thermal stability due to the suppressive thermal quenching behavior of Cr3+ ions. Ultimately, by mixing the Sr2GaTaO6/Cr3+, Yb3+ phosphor with an epoxy adhesive and coating on a 460 nm blue LED chip, an NIR pc-LED device was successfully fabricated, and its prospective usage in nondestructive testing and night vision fields was evaluated. This work contributes to the exploration of blue light effectively stimulating broad-band NIR-emitting phosphors.

Thermal Enhanced Near-Infrared Upconversion Luminescence in Y2Mo4O15:Yb/Nd with Uniaxial Negative Thermal Expansion

Thermal quenching (TQ) of luminescence presents a significant barrier to the effective use of optical thermometers in high-temperature applications. Herein, we report a novel uniaxial negative thermal expansion (NTE) phosphor, Y2-2x-2yMo4O15:xYb,yNd, synthesized by a solid-state reaction. Under 980 nm laser excitation, it exhibits excellent thermally enhanced near-infrared (NIR) upconversion luminescence (UCL) performance. The UCL intensities of Nd3+ at 573 K were enhanced by 396-fold (750 nm), 57.6-fold (810 nm), and 7.6-fold (882 nm), respectively, compared with that of room temperature. In situ temperature-dependent X-ray diffraction and steady- and transient-state spectra are used to reveal thermal expansion behavior and luminescence mechanism in detail. The thermal enhancement of NIR UCL is attributed to the synergistic effect of increased radiative transition probability due to the anisotropic thermal expansion of the crystal and the enhanced energy transfer (ET) efficiency resulting from uniaxial shrinkage and the phonon-assisted process. Based on the luminescence intensity ratio (LIR) of the thermally coupled energy levels (4F7/2/4F3/2), the target sample achieved ultrahigh sensitivity (Sr = 3.0% K-1 at 298 K) with high repeatability over the entire temperature range. This study not only provides a fresh perspective for achieving thermal enhancement of NIR UCL phosphors using uniaxial negative thermal expansion materials but also presents a novel approach for developing NIR UCL optical thermometers with outstanding temperature performance.

Ca2+/Si4+ Modification of the (Gd,Lu)AG Garnet for Enhanced Broadband Cr3+ Luminescence of High Thermal Stability

Near-infrared (NIR)-emitting phosphors with high quantum efficiency and thermal stability are crucial to NIR pc-LEDs. Garnet-structured (GdLuCa)(Al4-zSiCrz)O12 (z = 0.01-0.2) and (Gd2-xLuCax)(Al4.95-xSixCr0.05)O12 (x = 0.2-1.0) new phosphors with promising NIR luminescence under blue light excitation were designed and fabricated by a solid-state reaction in this work. It was analyzed that the Ca2+, Cr3+, and Si4+ ions would replace Gd3+ in [GdO8], Al1 in [Al1O6], and Al2 in [Al2O4], respectively, and the optimal Cr3+ content is z = 0.05, above which concentration quenching would occur via an electric dipole-dipole interaction. Increasing Ca2+/Si4+ substitution up to x = 1.0 led to luminescence enhancement by a factor of up to 1.85 and internal/external quantum efficiency (%) increment from ∼25.9/10.7 to 63.4/27.5, and all of the phosphors showed excellent thermal stability (I423 K/I298 K ≥ 87.6%). The luminescence properties of Cr3+ were discussed in detail through systematic investigation of the effects of Cr3+ and Ca2+/Si4+ contents on the crystal structure, local coordination, and crystal field. With the NIR pc-LED device integrated from the optimal phosphor (x = 1.0) and a blue LED chip, electroluminescence manifested potential applications in night vision and medical diagnosis.

Cr3+-Doped LiAlO2 NIR-I Emitting Phosphors with Superior Resistance to Thermal Quenching for Night Vision Monitoring and Bioimaging

Near-infrared phosphor-converted light-emitting diodes (NIR pc-LEDs) as a new NIR light source has outstanding application potential in the fields of NIR spectroscopy analysis, sensing, imaging, and pattern recognition. Therefore, the development of NIR phosphors with good NIR luminescence thermal stability has attracted much attention. To this end, we developed LiAlO2:Cr3+ garnet-type NIR phosphors by a high-temperature solid-state reaction method. Under 405 nm excitation, the Cr3+ ions located in tetrahedrons of LiAlO2 emit NIR emission in a broadband NIR emission that covers 650-900 nm mixed with several sharp narrowband R-line emissions, which showed excellent luminescence thermal stability with integrated intensity of emission measured at 573 K is ∼90.86% of that measured at 303 K caused by good structural rigidity and low thermal expansion coefficient of the matrix material. An NIR pc-LED device assembled with the optimized LiAlO2:Cr3+ and a commercially available purple LED chip emitted NIR output power of ∼98.172 mW at a driving current of 300 mA and demonstrated an electro-optical conversion efficiency of ∼9.09%, while demonstrated it has excellent application potential in the fields of night vision monitoring and biomedical imaging.

Broadband Ca3MgZrGe3O12:Cr3+ garnet phosphor for high-performance NIR pc-LED application

The near-infrared (NIR) phosphor-converted light-emitting diode (pc-LED) is heavily reliant upon the performance of NIR phosphors. However, the current NIR pc-LEDs suffer from low photoelectric efficiency and insufficient near-infrared output power. In this study, Cr3+-doped Ca3MgZrGe3O12 phosphors leading to high-performance NIR pc-LEDs were developed for the first time. They feature robust and wide NIR emission that extends over the spectrum from 650 to 1100 nm with a full width at half maximum of 120 nm, a high quantum yield of 82% and excellent thermal stability of T50% = 250 °C and I150 °C = 80% when excited at 460 nm. The NIR pc-LED was constructed by combining the Ca3MgZrGe3O12:0.04Cr3+ phosphor with a blue LED chip, resulting in a device that exhibits a photoelectric conversion efficiency of 20% and a near-infrared output power of 54.19 mW when operated at a current of 100 mA. The obtained luminous efficacy is superior to that of the vast majority of current broadband near-infrared pc-LEDs. In addition, this NIR pc-LED exhibits strong penetration and its applications in bio-imaging are demonstrated. The results indicate that Ca3MgZrGe3O12:Cr3+ NIR broadband phosphors are efficient for NIR pc-LEDs.

Achieving a Balance of Good Quantum Efficiency and Thermal Stability in the Y2CaScAl3GeO12:Cr3+ Broadband Phosphor for Multiple NIR Spectroscopy Applications

Near-infrared phosphor-converted light emitting diodes (NIR pc-LEDs) are considered as desirable NIR light sources to satisfy current needs owing to their numerous remarkable features. Nevertheless, as an essential component, previously reported NIR phosphors with broadband emission often suffer from inferior efficiency or thermal stability, therefore restricting their use and promotion. Herein, a novel Cr3+-doped garnet phosphor Y2CaScAl3GeO12:Cr3+ (YCSAG:Cr3+) is developed via regulating the near-neighbor coordination polyhedron. Under the excitation of blue light, it exhibits a broadband NIR emission peaking near 800 nm with a full width at half-maximum (fwhm) exceeding 150 nm, owing to the increased structural distortion of the octahedron. Particularly, due to the enhanced local structural rigidity induced by lattice shrinkage, the optimal sample achieves a balance of high internal quantum efficiency (IQE) of approximately 83% and thermal stability of approximately 90% at 393 K, facilitating its practical application as an NIR light source. Eventually, using the typical YCSAG:0.04Cr3+ phosphor and 450 nm blue LED chip, a high-performance NIR pc-LED device has been manufactured, demonstrating potential applications in anticounterfeiting and night vision.

Efficient and Tunable Near-Infrared Luminescence in Cubic Phosphate K2AlTi(PO4)3:Cr3+ for Spectroscopy Applications

Broadband near-infrared (NIR) phosphors are crucial components of NIR phosphor-converted light-emitting diode (pc-LED) sources for various smart spectroscopy applications. However, developing an efficient, tunable, and inexpensive broadband NIR phosphor with sufficient spectral coverage remains a great challenge. In this work, a cubic phosphate K2AlTi(PO4)3 with highly structural rigidity was chosen as host material for Cr3+ substitution to create an efficient NIR emission. Synthesizing this compound, the obtained material exhibits a broadband NIR emission covering 700-1200 nm with a peak wavelength ranging from 820 to 860 nm depending on the Cr3+ substituting concentration. The Cr3+ concentration optimized sample possesses a photoluminescence quantum yield (PLQY) of 76.4% with an emission peak centered at 857 nm and a full width at half-maximum (fwhm) of 184 nm under 464 nm exaction, demonstrating an efficient and relatively long-wavelength NIR emission with wide spectral coverage. This broadband NIR emission is mainly derived from a single kind of emission center deduced from spectral analysis, luminescence dynamics, and first-principle calculations. Using this material, the fabricated NIR pc-LED device presents an excellent NIR output power and NIR photoelectric conversion efficiency, making this material attractive in practical applications of night-vision and bioimaging. Therefore, this work not only provides a broadband NIR material with superiorities of low cost, high efficiency, wide-range tunability, wide spectral coverage, and relatively long-wavelength NIR emission for spectroscopy applications but also highlights some clues to discover this kind of materials.

Realizing Ultrabroadband NIR-II Emission and Wide-Range Wavelength Tuning in Cr4+-activated ABO2 (A = Li, Na; B = Al, Ga) Phosphors

Cr4+-activated phosphors are important candidate materials for NIR-II light sources, but providing a suitable lattice coordination environment for Cr4+ and achieving long wavelength broadband emission remains a challenge. In this work, a series of Cr4+-activated ABO2 (A = Li, Na; B = Al, Ga) phosphors were successfully prepared. Due to the presence of only tetrahedral coordination structures available for Cr4+ to occupy in the matrix crystal ABO2, the valence state and luminescence stability of Cr4+ are effectively guaranteed. Through the cation substitution design of A-site (Na → Li) and B-site (Ga → Al), the [BO4] tetrahedron is distorted and expanded, which degrades the symmetry of the Cr4+ coordination crystal field. Consequently, the central wavelength of the Cr4+ emission peak is tuned from 1280 to 1430 nm, and the fwhm is significantly extended from 257 to 355 nm. Thebroadband NIR-II light sources constructed with LiAlO2: 0.03Cr4+ and NaGaO2: 0.03Cr4+ phosphors verify their important potential applications in nondestructive testing and biological imaging.

Near-Infrared Light Emitting Metal Halides: Materials, Mechanisms, and Applications

Near-Infrared (NIR) light emitting metal halides are emerging as a new generation of optical materials owing to their appealing features, which include low-cost synthesis, solution processability, and adjustable optical properties. NIR-emitting perovskite-based light-emitting diodes (LEDs) have reached an external quantum efficiency (EQE) of over 20% and a device stability of over 10,000 h. Such results have sparked an interest in exploring new NIR metal halide emitters. In this review, several different types of NIR-emitting metal halides, including lead/tin bromide/iodide perovskites, lanthanide ions doped/based metal halides, double perovskites, low dimensional hybrid and Bi3+/Sb3+/Cr3+ doped metal halides, are summarized, and their recent advancement is assessed. The characteristics and mechanisms of narrow-band or broadband NIR luminescence in all these materials are discussed in detail. Also, the various applications of NIR-emitting metal halides are highlighted and an outlook for the field is provided.

The luminescence modulation of rare earth-doped/containing lead-free double perovskites toward multifunctional applications: a review

Lead-free double perovskites (DPs) with superior environmental stability and high defect tolerance have attracted considerable attention and exhibit great promise in photodetectors, solar cells, lighting devices, etc. However, achieving optical modulation and high photoluminescence quantum yield using this kind of material remains a challenge. Rare earth ions feature abundant energy levels and outstanding photophysical properties. Incorporating rare earth ions into lead-free DPs is an effective strategy to improve their optical performances, which have great effects on night-vision and light emitting diodes. Consequently, in this mini-review, we summarize the synthesis methods, optical properties, issues, and multifunctional applications of lead-free DPs described in recent years. The performances of DPs can be modulated via rare earth doping, which involves the extension of luminescence range, the improvement of PLQY, the realization of multi-mode excitation, and the regulation of luminescence color. We hope that this review will provide some insights into luminescence modulation and applications of lead-free DPs.

Broadband short-wave near-infrared-emitting phosphor MgNb2O6:Cr3+ for pc-LED applications

Broadband short-wave near-infrared (NIR) phosphor-converted light-emitting diodes (pc-LEDs) have been attracting keen interest for miniature NIR spectroscopy, while still lacking sufficient novel broadband NIR-emitting phosphors. Herein, we report a novel MgNb2O6:Cr3+ polycrystalline phosphor with a broad NIR emission band centered at 970 nm and a large full-width at half-maximum of approximately 155 nm under excitation of bluish-green light at around 515 nm. The optimized phosphor MgNb2O6:1%Cr3+ features a high internal quantum efficiency (IQE) of ∼85.5% and a moderate external QE of 25.2%. The fluorescence properties determined by two distorted hexa-coordination octahedral sites (i.e. [MgO6] and [NbO6]), low crystal field strength (Dq/B ∼ 1.65), and Cr3+-doping concentration were systematically investigated for comprehensive understanding of photophysical mechanisms. Besides, this broadband NIR phosphor MgNb2O6:Cr3+ exhibits a moderate thermal quenching of 21.4%@373 K for pc-LED application. An NIR pc-LED self-built by combining the optimal phosphor with a commercial cyan of ∼515 nm exhibits an NIR output power increase from 3.19 to 11.38 mW as the drive current is varied from 40 to 220 mA. With the help of this prototype pc-LED device, multiple applications were successfully performed to clearly recognize blood vessel distributions in the human finger, penetrate a plastic cap, and distinguish multi-color text. Undoubtedly, further development of such broadband short-wave NIR-emitting phosphors will make novel pc-LED devices for significant applications in biomedical imaging, nondestructive safety detection, intelligent identification, etc.

Mapping Uncharted Lead-Free Halide Perovskites and Related Low-Dimensional Structures

Research on perovskites has grown exponentially in the past decade due to the potential of methyl ammonium lead iodide in photovoltaics. Although these devices have achieved remarkable and competitive power conversion efficiency, concerns have been raised regarding the toxicity of lead and its impact on scaling up the technology. Eliminating lead while conserving the performance of photovoltaic devices is a great challenge. To achieve this goal, the research has been expanded to thousands of compounds with similar or loosely related crystal structures and compositions. Some materials are "re-discovered", and some are yet unexplored, but predictions suggest that their potential applications may go beyond photovoltaics, for example, spintronics, photodetection, photocatalysis, and many other areas. This short review aims to present the classification, some current mapping strategies, and advances of lead-free halide double perovskites, their derivatives, lead-free perovskitoid, and low-dimensional related crystals.

An efficient and thermally stable Cr3+-activated Y2GdSc2Al2GaO12 garnet phosphor for NIR spectroscopy applications

Near-infrared (NIR) spectroscopy realized by an NIR phosphor-converted light-emitting diode (pc-LED) as a light source has aroused considerable interest due to its numerous merits and widespread application scenarios. Nevertheless, developing NIR emitting phosphors with high performance is still the top priority. Here, we report a new Y2GdSc2Al2GaO12:Cr3+ (YGSAG:Cr3+) garnet phosphor, which demonstrates a broadband emission peaking at 754 nm with a full width at half maximum (FWHM) of around 120 nm in the range of 650-1200 nm. The YGSAG:0.08Cr3+ sample irradiated by blue light exhibits the most intense emission intensity, leading to a high absorption efficiency of 49.54%. In addition, compared with room temperature, the integrated PL intensity of the sample can still be maintained at 90.97% at 423 K. Benefitting from the outstanding optical properties, the as-manufactured NIR pc-LED device driven by a 100 mA current represents a high NIR output power of 35.14 mW and a photoelectric efficiency of 12.51%. These results verify that the as-synthesized YGSAG:Cr3+ phosphor possesses great potential for the applications of NIR spectroscopy.

Broadband La2LiSbO6: Cr3+ Phosphors with Double Luminescent Centers for NIR pc-LEDs

The La2LiSbO6: xCr3+ phosphors were synthesized by means of a high-temperature solid-phase method. Based on the differences in ionic radius, valence state, and formation energy, the substitution sites of Cr3+ ions are discussed in detail. The optimized doping concentration of Cr3+ is determined to be 0.01. Under 517 nm excitation, the La2LiSbO6: 0.01Cr3+ phosphor presents a wide emission band (from 700 to 1350 nm) with a peak centered at 952 nm. Additionally, its corresponding full width at half-maximum is 155 nm, and the internal quantum efficiency reaches 62.4%. Meanwhile, the emission intensity of the La2LiSbO6: 0.01Cr3+ phosphor at 373 K is about 63.7% of that at room temperature, exhibiting good thermal stability. Aiming to fabricate a near-infrared phosphor-converted light-emitting diode device, the La2LiSbO6: 0.01Cr3+ phosphor is mixed with epoxy adhesive and cured on a green light-emitting diode chip. Under the irradiation of the fabricated light-emitting diode device, fruits and writing in the dark environment can be captured by a near-infrared camera. Hence, the La2LiSbO6: 0.01Cr3+ phosphor is promising for night vision.

Highly efficient near-infrared solid solution phosphors with excellent thermal stability and tunable spectra for pc-LED light sources toward NIR spectroscopy applications

Near-infrared (NIR) luminescent materials have attracted wide research interest due to their unique photophysical properties for designing NIR light-emitting diodes (NIR LEDs). Here, a series of Cr3+-activated NIR-emitting solid solution phosphors, Gd1-xLux(Al1-xScx)3(BO3)4:0.01Cr3+ (GLASB:Cr3+) (x = 0 to 0.5), are successfully synthesized via a cosubstitution approach. The GLASB:Cr3+ phosphors reveal extraordinary optical performance with a desirable high IQE of 93.6%, considerable broadened FWHM (from 128 nm to 196 nm) and redshift of 119 nm (747 → 866 nm) as the amount of [Lu3+-Sc3+] ion doping increases. Moreover, their photoluminescent thermal stability is substantially improved, maintaining 105.7% of the initial integral intensity up to 150 °C, namely zero-thermal-quenching. The NIR pc-LED fabricated using the GLASB:Cr3+ phosphor generates an NIR output power of 46 mW and an electro-optical efficiency of 37% at a 120 mA input current. Finally, the characteristic NIR emission of this phosphor can not only be utilized in the fields of night-vision technology and biometric identification, but also exhibits a perfect match with the absorption of the bacteriochlorophyll (BChl) and light-harvesting protein (LHP) of photosynthetic bacteria (PSB), presenting a high application prospect for improving PSB photosynthesis.

Synthesis and Optimization of Cs2B'B″X6 Double Perovskite for Efficient and Sustainable Solar Cells

Hybrid perovskite materials with high light absorption coefficients, long diffusion lengths, and high mobility have attracted much attention, but their commercial development has been seriously hindered by two major problems: instability and lead toxicity. This has led to lead-free halide double perovskite becoming a prominent competitor in the photovoltaic field. For lead-free double perovskites, Pb2+ can be heterovalent, substituted by non-toxic metal cations as a double perovskite structure, which promotes the flexibility of the composition. However, the four component elements and low solubility in the solvent result in synthesis difficulties and phase impurity problems. And material phase purity and film quality are closely related to the number of defects, which can limit the photoelectric performance of solar cells. Therefore, based on this point, we summarize the synthesis methods of Cs2B'B″X6 double perovskite crystals and thin films. Moreover, in the application of solar cells, the existing research mainly focuses on the formation process of thin films, band gap adjustment, and surface engineering to improve the quality of films and optimize the performance of devices. Finally, we propose that Cs2B'B″X6 lead-free perovskites offer a promising pathway toward developing highly efficient and stable perovskite solar cells.

Achieving Broadband NIR-I to NIR-II Emission in an All-Inorganic Halide Double-Perovskite Cs2NaYCl6:Cr3+ Phosphor for Night Vision Imaging

Near-infrared phosphor-converted light-emitting diodes (NIR pc-LEDs) offer numerous advantages, including compact size, tunable emission spectra, energy efficiency, and high integration potential. These features make them highly promising for various applications, such as night vision monitoring, food safety inspection, biomedical imaging, and theragnostics. All-inorganic halide double-perovskite materials, known for their large absorption cross section, excellent defect tolerance, and long carrier diffusion radius, serve as unique matrices for constructing near-infrared fluorescent materials. In this study, we successfully prepared the all-inorganic metal halide double-perovskite Cs2NaYCl6:Cr3+ using a grinding-sintering method. A small fraction of the [YCl6] octahedra within the host material's lattice was substituted with Cr3+ ions, resulting in the creation of the Cs2NaYCl6:Cr3+ phosphor. When excited with λ = 310 nm UV light, the phosphor exhibited a broad emission range spanning from 800 to 1400 nm, covering the NIR-I and NIR-II regions. It had a broad bandwidth emission of 185 nm and achieved a fluorescence quantum yield of 20.2%. The unique broadband emission of the phosphor originates from the weak crystal field environment provided by the Cs2NaYCl6 host matrix, which enhances the luminescence properties of the Cr3+ ions. To create NIR pc-LEDs, the phosphor was encapsulated onto a commercially available UV LED chip operating at 310 nm. The potential application of these NIR pc-LEDs in night vision imaging was successfully validated.

Near-Infrared Photoluminescence from Ytterbium- and Erbium-Codoped CsPbCl3 Perovskite Quantum Dots with Negative Thermal Quenching

Near-infrared (NIR) luminescent phosphors hold promise for a wide range of applications, from bioimaging to light-emitting diodes (LEDs), but are typically confined to wavelengths <1300 nm and manifest substantial thermal quenching pervasive in luminescent materials. Here we observed the thermally enhanced NIR luminescence of Er³⁺ (1540 nm), a 2.5-fold enhancement with increasing temperature from 298 to 356 K, from Yb³⁺- and Er³⁺-codoped CsPbCl₃ perovskite quantum dots (PQDs) (photoexcited at ∼365 nm). Mechanistic investigations revealed that thermally enhanced phenomena originated from combined effects of thermally stable cascade energy transfer (from a photoexcited exciton to a pair of Yb³⁺ and then to surrounding Er³⁺) and minimized quenching of surface-adsorbed water molecules on the ⁴I_13/2 state of Er³⁺ induced by the temperature increase. Importantly, these PQDs enable producing phosphor-converted LEDs emitting at 1540 nm with inherited thermally enhanced properties, having implications for a wide range of photonic applications.

A universal hydrochloric acid-assistant powder-to-powder strategy for quick and mass preparation of lead-free perovskite microcrystals

Lead-free halide perovskite materials possess low toxicity, broadband luminescence and robust stability compared with conventional lead-based perovskites, thus holding great promise for eyes-friendly white light LEDs. However, the traditionally used preparation methods with a long period and limited product yield have curtailed the commercialization of these materials. Here we introduce a universal hydrochloric acid-assistant powder-to-powder strategy which can accomplish the goals of thermal-, pressure-free, eco-friendliness, short time, low cost and high product yield, simultaneously. The obtained Cs2Na0.9Ag0.1In0.95Bi0.05Cl6 microcrystals exhibit bright self-trapped excitons emission with quantum yield of (98.3 ± 3.8)%, which could retain (90.5 ± 1.3)% and (96.8 ± 0.8)% after continuous heating or ultraviolet-irradiation for 1000 h, respectively. The phosphor converted-LED exhibited near-unity conversion efficiency from ultraviolet chip to self-trapped excitons emission at ~200 mA. Various ions doping (such as Cs2Na0.9Ag0.1InCl6:Ln3+) and other derived lead-free perovskite materials (such as Cs2ZrCl6 and Cs4MnBi2Cl12) with high luminous performance are all realized by our proposed strategy, which has shown excellent availability towards commercialization.

Triangulating Dopant-Level Mn(II) Insertion in a Cs2NaBiCl6 Double Perovskite Using Magnetic Resonance Spectroscopy

Lead-free metal halide double perovskites are gaining increasing attention for optoelectronic applications. Specifically, doping metal halide double perovskites using transition metals enables broadband tailorability of the optical bandgap for these emerging semiconducting materials. One candidate material is Mn(II)-doped Cs₂NaBiCl₆, but the nature of Mn(II) insertion on chemical structure is poorly understood due to low Mn loading. It is critical to determine the atomic-level structure at the site of Mn(II) incorporation in doped perovskites to better understand the structure-property relationships in these materials and thus to advance their applicability to optoelectronic applications. Magnetic resonance spectroscopy is uniquely qualified to address this, and thus a comprehensive three-pronged strategy, involving solid-state nuclear magnetic resonance (NMR), high-field dynamic nuclear polarization (DNP), and electron paramagnetic resonance (EPR) spectroscopies, is used to identify the location of Mn(II) insertion in Cs₂NaBiCl₆. Multinuclear (²³Na, ³⁵Cl, ¹³³Cs, and ²⁰⁹Bi) one-dimensional (1D) magnetic resonance spectra reveal a low level of Mn(II) incorporation, with select spins affected by paramagnetic relaxation enhancement (PRE) induced by Mn(II) neighbors. EPR measurements confirm the oxidation state, octahedral symmetry, and low doping levels of the Mn(II) centers. Complementary EPR and NMR measurements confirm that the cubic structure is maintained with Mn(II) incorporation at room temperature, but the structure deviates slightly from cubic symmetry at low temperatures (<30 K). HYperfine Sublevel CORrelation (HYSCORE) EPR spectroscopy explores the electron-nuclear correlations of Mn(II) with ²³Na, ¹³³Cs, and ³⁵Cl. The absence of ²⁰⁹Bi correlations suggests that Bi centers are replaced by Mn(II). Endogenous DNP NMR measurements from Mn(II) → ¹³³Cs (<30 K) reveal that the solid effect is the dominant mechanism for DNP transfer and supports that Mn(II) is homogeneously distributed within the double-perovskite structure.

Perspective and Prospects on persistent luminescent nanoparticles for biological imaging and tumor therapy

Persistent luminescent nanoparticles (PLNPs) are photoluminescent materials that can still emit luminescence after the cessation of the excitation light source. In recent years, due to their unique optical properties, the PLNPs have attracted extensive attention in the biomedical field. Since the PLNPs effectively eliminate autofluorescence interference from biological tissues, many researchers have contributed a lot of work in the fields of biological imaging and tumor therapy. This article mainly introduces the synthesis methods of the PLNPs and their progress in the application of biological imaging and tumor therapy, as well as the challenges and development prospects.

[Zn2+-Ge4+] co-substitutes [Ga3+-Ga3+] to coordinately broaden the near-infrared emission of Cr3+ in Ga2O3 phosphors

Here, a "chemical unit co-substitution" method is used to improve the near-infrared (NIR) emission of phosphors, using [Zn²⁺-Ge⁴⁺] to co-substitute [Ga³⁺-Ga³⁺] sites to reduce crystal field splitting to affect the structure of gallium oxide. A series of broadband NIR phosphors are synthesized by a high-temperature solid-phase method, and their phase structures, crystal structures, morphologies, diffuse reflectance spectra, and luminescence lifetimes are investigated. The Ga_1.68(Zn-Ge)_0.3O₃:0.02Cr³⁺ (GZGOC) phosphor exhibits NIR wide-band emission, with a peak wavelength of 766 nm and a half-width of 138 nm. Meanwhile, the quantum yield of photoluminescence can reach 81.2%. The phosphor has good thermal stability. When the temperature reaches 373 K, its emission intensity still remains at 73.4% of that at room temperature. A 460 nm LED chip and this phosphor are used to fabricate a phosphor-converted light emitting diode (pc-LED) device which can be used as a NIR light source. All these results show the application potential of the as-prepared phosphor in NIR imaging.

Alloying Bi-Doped Cs2Ag1-xNaxInCl6 Nanocrystals with K+ Cations Modulates Surface Ligands Density and Photoluminescence Efficiency

We show how, in the synthesis of yellow-emissive Bi-doped Cs2Ag1-xNaxInCl6 double perovskite nanocrystals (NCs), preventing the transient formation of Ag0 particles increases the photoluminescence quantum yield (PLQY) of the NCs from ∼30% to ∼60%. Calculations indicate that the presence of even a single Ag0 species on the surface of a NC introduces deep trap states. The PL efficiency of these NCs is further increased to ∼70% by partial replacement of Na+ with K+ ions, up to a 7% K content, due to a lattice expansion that promotes a more favorable ligands packing on the NC surface, hence better surface passivation. A further increase in K+ lowers the PLQY, due to both the activation of nonradiative quenching channels and a lower oscillator strength of the BiCl6→AgCl6 transition (through which PL emission occurs). The work indicates how a deeper understanding of parameters influencing carrier trapping/relaxation can boost the PLQY of double perovskites NCs.

Studies on the photoelectronic properties of a manganese (Mn)-doped lead-free double perovskite

Taking Cs₂NaBiCl₆, Cs₂AgInCl₆ and Cs₂AgBiCl₆ as examples of lead-free double perovskites (DPs), we study the photoluminescence (PL) properties of Mn-doped DPs. The electron localization function (ELF) reveals the more ionic nature of the Na-Cl bond in Cs₂NaBiCl₆ than that of the Ag-Cl bond in Cs₂AgBiCl₆. Bader charge calculations confirm the nominal +2 valence state of Mn ions in both DPs. Mn²⁺ ions introduce two defect levels in the band gap of the Cs₂NaBiCl₆ host, accounting for the d-d transition (⁴T₁-⁶A₁ transition) of Mn²⁺ and thus the subsequent orange PL. The changes of the crystal field and their influences on the emission energy of Mn²⁺ ions in different DPs are evaluated by calculating the Racah parameters (B and C) and the crystal field strength (Dq) obtained from energies of the terms of d⁵ in the Cs₂NaBiCl₆:Mn²⁺ and Cs₂AgInCl₆:Mn²⁺ systems. The results show that Dq in Cs₂AgInCl₆:Mn²⁺ is stronger than that in Cs₂NaBiCl₆:Mn²⁺. The analyses on bonding interactions of the Mn-Cl bond via ELF and the integrated projected pCOHP also confirm the stronger ionic bonding interactions and thus the boost of the crystal field strength in the Cs₂AgInCl₆:Mn²⁺ system, which results in the blue-shift of the Mn²⁺ introduced PL peak from Cs₂AgInCl₆ to Cs₂NaBiCl₆. Our results provide a new strategy to modulate the emission wavelengths, i.e., tuning the crystal field.

Green Triplet Self-Trapped Exciton Emission in Layered Rb3Cd2Cl7:Sb3+ Perovskite: Comparison with RbCdCl3:Sb3

Metal halide materials have recently sparked intense research because of their excellent photophysical properties and chemical stability. For example, RbCdCl₃:Sb³⁺ exhibits broad emission at about 600 nm with a high photoluminescence quantum yield (PLQY) over 91% and double emission bands with bright white color. Herein, we obtained a novel Rb and Cd layered perovskite Rb₃Cd₂Cl₇ doped with Sb³⁺, which gives luminescence at 525 nm with a large Stokes shift of 200 nm, originating from a self-trapped exciton (STE). Its PLQY is 57.47%, but its low-temperature PLQY becomes much higher at the same wavelength. When Rb₃Cd₂Cl₇:Sb³⁺ and RbCdCl₃:Sb³⁺ were compared, the two classes of quantum confinement effects by Rb and Cd ions in the lattice were identified to describe their electronic states and different optical properties. These results suggest that properties of Sb-doped cadmium halides could be modified by the structure type and local atomic confinement to find applications as promising luminescent materials for optoelectronic devices.

Efficient near-infrared broadband garnet phosphor for pc-LED and its application to vascular visualization and night vision

Ultra-broadband near-infrared (NIR) spectroscopy has unparalleled application prospects in intelligent detection and phosphor-converted light-emitting diodes (pc-LED), which are most likely to become the next generation of NIR light sources, has become a hot spot for research nowadays. To cope with the demand for more NIR spectroscopy applications, more efficient NIR phosphors need to be developed. Here, by screening the subject with a smaller band gap and by screening the suitable ion electronegativity of the lattice position where the Cr³⁺ is located, and then through the energy transfer, a series of Gd₃Zn₂GaGe₂O₁₂:xCr³⁺, yYb³⁺ (GZGG:Cr³⁺/Yb³⁺) NIR broadband garnet phosphors were found for the first time. By controlling the energy transfer process, the internal quantum yield (IQY) (54.9%), external quantum yield (EQY) (24.65%), bandwidth (260 nm), and thermal stability (60% at 150 °C) of NIR emission were substantially improved. The obtained phosphors are packaged with blue light chips into pc-LED, which can be applied in different fields such as vascular visualization and night vision.

Modulation of Thermally Stable Photoluminescence in Cr3+-Based Near-Infrared Phosphors

Broadband near-infrared (NIR) light sources based on phosphor-converted light-emitting diodes (pc-LEDs) are desirable for various photonics applications, while developing thermally stable NIR phosphors remains a great challenge. Increasing the temperature accelerates the severe nonradiative relaxation process gorverned by the intrinsic energy gap law, which further suspends the efficient low-energy emission of Cr³⁺ emitters in the inorganic lattice. To address this rule, several state-of-the-art strategies have been put forward in this perspective to modulate the critical law from the viewpoints of (1) crystal structure design, (2) defect engineering, (3) strengthened rigidity, and (4) energy transfer. This perspective suggests avenues for exploring novel broadband NIR phosphors with high thermal stability and will also stimulate further studies on NIR spectroscopy for high-power applications.

Efficient Yellow Self-Trapped Exciton Emission in Sb3+-Doped RbCdCl3 Metal Halides

Metal halide perovskites have flexible crystal and electronic structures and adjustable emission characteristics, which have very broad applications in the optoelectronic field. Among them, all-inorganic perovskites have attracted more attention than others in recent years because of their characteristics of large diffusion length, high luminescence efficiency, and good stability. In this work, Sb³⁺-doped RbCdCl₃ crystalline powder was synthesized by a simple hydrothermal method, and its luminescence properties were studied, which showed a broad emission band with a large Stokes shift and efficient yellow light emission at about 596 nm at room temperature with a photoluminescence quantum yield of 91.7%. The emission came from the transition of the self-trapped exciton 1 (STE1) out of ³P_n (n = 0, 1, and 2) to S₀ due to strong electron-phonon coupling, which scaled with increasing temperature. Moreover, its emission color became white at low temperatures due to the occurrence of transition of other self-trapped exciton 0 (STE0) state emission out of the ¹S states of Sb ions to S₀ in the lattice. These emission color changes may be used for temperature sensing, and this Sb³⁺-doped RbCdCl₃ material expands the knowledge of the efficient luminescent inorganic material family for further applications of all-inorganic perovskites.

Highly efficient Fe3+-doped A2BB'O6 (A = Sr2+, Ca2+; B, B' = In3+, Sb5+, Sn4+) broadband near-infrared-emitting phosphors for spectroscopic analysis

Near-infrared (NIR)-emitting phosphor-converted light-emitting diodes have attracted widespread attention in various applications based on NIR spectroscopy. Except for typical Cr³⁺-activated NIR-emitting phosphors, next-generation Cr³⁺-free NIR-emitting phosphors with high efficiency and tunable optical properties are highly desired to enrich the types of NIR luminescent materials for different application fields. Here, we report the Fe³⁺-activated Sr_2-yCa_y(InSb)_1-zSn_2zO₆ phosphors that exhibit unprecedented long-wavelength NIR emission. The overall emission tuning from 885 to 1005 nm with broadened full-width at half maximum from 108 to 146 nm was realized through a crystallographic site engineering strategy. The NIR emission was significantly enhanced after complete Ca²⁺ incorporation owing to the substitution-induced lower symmetry of the Fe³⁺ sites. The Ca₂InSbO₆:Fe³⁺ phosphor peaking at 935 nm showed an ultra-high internal quantum efficiency of 87%. The as-synthesized emission-tunable phosphors demonstrated great potential for NIR spectroscopy detection. This work initiates the development of efficient Fe³⁺-activated broadband NIR-emitting phosphors and opens up a new avenue for designing NIR-emitting phosphor materials.

Chemical Potential Diagram Guided Rational Tuning of Electrical Properties: A Case Study of CsPbBr3 for X-ray Detection

Controlling the carrier polarity and concentration underlies most electronic and optoelectronic devices. However, for the intensively studied lead halide perovskites, the doping tunability is inefficient. In this work, taking CsPbBr₃ as an example, it is revealed that the coexistence of metallic Pb or CsBr₃ /Br₂ , rather than the precursor ratio, can provide Pb-rich/Br-poor or Br-rich/Pb-poor chemical conditions, enabling the tunability of electrical properties from weak n-type, intrinsic, to moderate p-type. Experimentally, under Br₂ -exposure treatment, a shift of the Fermi level as large as 1.00 eV is achieved, which is one of the highest value among all kinds of doping methods. The X-ray detector based on the intrinsic CsPbBr₃ exhibits excellent performance, with a negligible dark-current drift of 7.1 × 10^-4 nA cm^-1 s^-1 V^-1 , a low detection limit of 103.6 nGy_air s^-1 , and a high sensitivity of 9085 μC Gy_air ^-1 cm^-2 . This work provides a critical understanding and guidance for tuning the electrical properties of lead halide perovskites, which establishes good foundations for achieving intrinsic perovskite semiconductors and also constructing potential homojunction devices.

Facile Melting-Crystallization Synthesis of Cs2NaxAg1-xInCl6: Bi Double Perovskites for White Light-Emitting Diodes

Lead-free double perovskites (DPs) have outstanding luminescent properties, which make them excellent candidates for wide use in optoelectronics. Herein, a solvent-free melting-crystallization technique, which can produce kilogram-scale DP microcrystals (DP-MCs) in one batch, is invented to synthesize the Cs₂Na_xAg_1-xInCl₆: Bi (x = 0, 0.2, 0.4, 0.6, 0.8, and 1) DP-MCs. The structure and composition analysis confirmed the products are pure Cs₂Na_xAg_1-xInCl₆ DP-MCs. Affected by Jahn-Teller distortion of AgCl₆ octahedra, self-trapped excitons appear in the excited state, resulting in the broadband emission (400-850 nm) of Cs₂Ag_1-xNa_xInCl₆: Bi DP-MCs. The enhancement of the photoluminescence quantum yield can be realized by introducing Na⁺ to break the parity-forbidden transition in the Cs₂AgInCl₆ DP. Optimized Cs₂Na_0.4Ag_0.6InCl₆: Bi DP-MC phosphors combined with commercial blue and green phosphors were coated on ultraviolet chips (365 nm) to fabricate white light-emitting diodes (WLEDs) from warm white (2930 K) to cold white (6957 K). An ultrahigh color rendering index of 97.1 and a CCT of 5548 K as well as Commission Internationale de l'Eclairage color coordinates of (0.331, 0.339) have been demonstrated. This kilogram-scale synthesis technique could stimulate the industrial development of WLEDs for general lighting based on DP-MC phosphors.

Boosting the Self-Trapped Exciton Emission in Alloyed Cs2 (Ag/Na)InCl6 Double Perovskite via Cu+ Doping

Fundamental understanding of the effect of doping on the optical properties of 3D double perovskites (DPs) especially the dynamics of self-trapped excitons (STEs) is of vital importance for their optoelectronic applications. Herein, a unique strategy via Cu⁺ doping to achieve efficient STE emission in the alloyed lead-free Cs₂ (Ag/Na)InCl₆ DPs is reported. A small amount (1.0 mol%) of Cu⁺ doping results in boosted STE emission in the crystals, with photoluminescence (PL) quantum yield increasing from 19.0% to 62.6% and excitation band shifting from 310 to 365 nm. Temperature-dependent PL and femtosecond transient absorption spectroscopies reveal that the remarkable PL enhancement originates from the increased radiative recombination rate and density of STEs, as a result of symmetry breakdown of the STE wavefunction at the octahedral Ag⁺ site. These findings provide deep insights into the STE dynamics in Cu⁺ -doped Cs₂ (Ag/Na)InCl₆ , thereby laying a foundation for the future design of new lead-free DPs with efficient STE emission.

Highly Sensitive Dual-Mode Optical Thermometry of Er3+/Yb3+ Codoped Lead-Free Double Perovskite Microcrystal

In this Letter, erbium (Er³⁺) and ytterbium (Yb³⁺) codoped perovskite Cs₂Ag_0.6Na_0.4In_0.9Bi_0.1Cl₆ microcrystal (MC) is synthesized and demonstrated systematically to the most prospective optical temperature sensing materials. A dual-mode thermometry based on fluorescence intensity ratio and fluorescence lifetime provides a self-reference and highly sensitive temperature measurement under dual wavelength excitation at a temperature from 300 to 470 K. Combined with the white-light emission derived from self-trapped excitons (STEs), the characteristic emission peak of Er³⁺ ions can be observed under 405 nm laser excitation. The fluorescence intensity ratio (FIR) between perovskite and Er³⁺ is used as temperature-dependent probe signal, of which maximum value for relative and absolute sensitivities reaches to 1.40% K^-1 and 8.20 × 10^-2 K^-1. Moreover, Er³⁺ luminescence becomes stronger with the feeding Yb³⁺ increasing under 980 nm laser excitation. The energy transfer of Er³⁺ and Yb³⁺ is revealed by power-dependent photoluminescence (PL) spectroscopy, and the involved upconversion mechanism pertains to the two-photon excitation process. The results reveal that the Er³⁺/Yb³⁺ codoped lead-free double perovskite MC is a good candidate for a thermometric material for the novel dual-mode design.

Light Emission Enhancement of (C3H10N)4Pb1-xMnxBr6 Metal-Halide Powders by the Dielectric Confinement Effect of a Nanosized Water Layer

Organic-inorganic hybrid metal halides have been widely studied as a kind of phosphor materials for high-performance white light-emitting diodes. In this paper, a series of organic-inorganic metal-halide (C₃H₁₀N)₄Pb_1-xMn_xBr₆ powders with different Mn²⁺ ion doping concentrations were synthesized by mechanochemical methods, giving broadband white light emission with a photoluminescence quantum yield of 36.1% at room temperature, which turn green with a much larger intensity at 80 K. Interestingly, its emission converted from white to red after 100 °C treatments and turned back to white again when exposed to moist air for a while. This emission variation was caused by the adsorbed water layer on the surface of product powders via the dielectric confinement. The red emission from no water powders is identified to occur from the Mn ferromagnetic pair in point-shared octahedral sites, while the broadband white emission originated from the surface water-assisted dielectric confinement and surface polarization which combine the self-trapped excitons and d-d transitions of Mn ions and Mn pairs in the product. Moreover, this white emission can transform into green color at 80 K with a much stronger intensity, caused by the even efficient surface dielectric confinement by the adsorbed frozen water layer. This special compound has the advantages of simple preparation, low cost, and good stability and even contains water molecule in the air, giving a near-perfect white emission, with CIE of (0.33, 0.35) and correlated color temperatures at around 5733 K, which may be used for different applications such as sensing, solid-state lighting, and display.

Efficient Cr3+-activated NaInP2O7 phosphor for broadband near-infrared LED applications

Recently, Cr3+-activated phosphors have garnered attention for broadband near-infrared phosphor converted light-emitting diodes (NIR pc-LEDs) applications, but usually display low efficiency. Herein, we designed and synthesized a novel efficient broadband NIR...

Photoelectrochemical performance of ligand-free CsPb2Br5 perovskites

A pure aqueous synthesis strategy for ligand-free CsPb2Br5 nanoplatelets and pure-phase single crystal is reported. The CsPb2Br5 perovskite displays excellent photoelectrochemical activity in the absence of other electron acceptors.

Cr3+-Doped double perovskite antimonates: efficient and tunable phosphors from NIR-I to NIR-II

By tuning cationic compositions, Cr3+-doped antimonate double perovskites present emissions from NIR-I to NIR-II regions. In particular, Ca2ScSbO6:Cr3+ and Sr2InSbO6:Cr3+ feature long-wavelength emissions with high luminescence efficiency.

Simultaneous enhancement of near infrared luminescence and stability of Cs2AgInCl6:Cr3+ double perovskite single crystals enabled by a Yb3+ dopant

Cs2AgInCl6:Cr3+,Yb3+ double perovskite single crystals was prepared by hydrothermal method, which shows NIR emission from 800 to 1400 nm with a peak at 1000 nm and a full-width at half maximum of 188 nm with a higher PLQY of ∼45% excited at 365 nm.

Blue-light-excited narrowing red photoluminescence in lead-free double perovskite Cs2−xKxAg0.6Na0.4In0.8Bi0.2Cl6−xBrx with cryogenic effects

The addition of KBr changed the original transition mode of the material and realized the blue-light excitation and narrow red emission of Cs2AgInCl6 at low temperatures.

Crystal-filed induced tuning of luminescence properties of Na3GaxAl1-xF6:Cr3+ phosphors with good thermal stability for NIR LEDs

Cr3+-activated broadband near-infrared (NIR) luminescence materials are attracting much attention for next-generation smart NIR light sources, which are widely used in night vision, bioimaging, medical treatments, and many other fields....

Efficient and thermally stable broadband near-infrared emission in a garnet Gd3In2Ga3O12:Cr3+ phosphor

A broadband garnet Gd3In2Ga3O12:Cr3+ NIR phosphor was successfully developed, and it has an optimized Cr3+ doping concentration as high as 9 mol%, generating a high quantum yield (85.3%) and ultra-high absorption efficiency (49.1%).

Near-Infrared Emitting Phosphor LaMg0.5(SnGe)0.5O3:Cr3+ for Plant Growth Applications: Crystal Structure, Luminescence, and Thermal Stability

Corresponding to the absorption curve of plant photosensitive pigment Pfr, near-infrared light has a broad application prospect in plant lighting. In order to explore this plant growth lamp, the novel near-infrared emitting phosphor LaMg0.5Sn0.5O3:Cr3+ was synthesized, which can be efficiently excited by 467 nm blue light. There are two luminescence centers, which were proven by testing the low-temperature spectrum, the excitation spectrum at different wavelengths, and the lifetime decay curve, and the two cell sequence substitution processes were obtained by Rietveld refinements of XRD. By introducing Ge4+, its luminescence intensity has been increased 1.6 times and the intensity at 150 °C remains at almost 80% that at room temperature. Finally, two different kinds of illumination experiments for plant growth were carried out, and the feasibility of the LaMg0.5(SnGe)0.5O3:Cr3+ phosphor for plant growth was confirmed.

Bandgap Modulation of Cs2AgInX6 (X = Cl and Br) Double Perovskite Nano- and Microcrystals via Cu2+ Doping

Recently, the double perovskite Cs₂AgInCl₆, which has high stability and low toxicity, has been proposed as a potential alternative to Pb-based perovskites. However, the calculated parity-allowed transition bandgap of Cs₂AgInCl₆ is 4.25 eV; this wide bandgap makes it difficult to use as an efficient solar absorber. In this study, we explored the effect of Cu doping on the optical properties of Cs₂AgInCl₆ double perovskite nano- and microcrystals (MCs), particularly in its changes of absorption profile from the ultraviolet (UV) to near-infrared (NIR) region. Undoped Cs₂AgInCl₆ showed the expected wide bandgap absorbance, but the Cu-doped sample showed a new sharp absorption peak at 419 nm and broad absorption bands near 930 nm, indicating bandgap reduction. Electron paramagnetic resonance (EPR) spectroscopy demonstrated that this bandgap reduction effect was due to the Cu doping in the double perovskite and confirmed that the Cu²⁺ paramagnetic centers were located on the surface of the nanocrystals (NCs) and at the center of the perovskite octahedrons (g_∥ > g_⊥ > g_e). Finally, we synthesized Cu-doped Cs₂AgInCl₆ MCs and observed results similar to those of the NCs, showing that the application range could be expanded to multidimensions.

A single luminescence center ultra-broadband near-infrared LiScGeO4:Cr phosphor for biological tissue penetration

In this work, in order to meet the application of near-infrared phosphor-converted light emitting diodes (pc-LEDs), an ultra-broadband emission phosphor, LiScGeO4:Cr, was synthesized. Its FWHM reaches 335 nm, and its emission spectrum ranges from 800 nm to 1650 nm, which almost covers the entire near-infrared second window (NIR-II). The broadband emission is thought to be caused by the 4T2 → 4A2 transition of the Cr3+ ion. This transition occurs due to the olivine structure of the crystal, which causes the Cr3+ ions to inhabit a low-symmetric crystal field, and the crystal field strength is very weak. NIR pc-LEDs were fabricated by combining a 460 nm blue LED with this phosphor, which penetrates 4 cm thick beef. The results indicate that there may be a potential application for this phosphor in the field of biological tissue penetration and non-destructive testing.

Efficient and Tunable Luminescence in Ga2-xInxO3:Cr3+ for Near-Infrared Imaging

Broadband near-infrared (NIR) emitting materials are in great demand as next-generation smart NIR light sources. In this work, a Cr³⁺-substituted phosphor capable of efficiently converting visible to NIR light is developed through the solid solution, Ga_2-xIn_xO₃:Cr³⁺ (0 ≤ x ≤ 0.5). The compounds were prepared using high-temperature solid-state synthesis, and the crystal and electronic structure, morphology, site preference, and photoluminescence properties are studied. The photoluminescence results demonstrate a high quantum yield (88%) and impressive absorption efficiency (50%) when x = 0.4. The NIR emission is tunable across a wide range (713-820 nm) depending on the value of x. Moreover, fabricating a prototype of a phosphor-converted NIR light-emitting diode (LED) device using 450 nm LED and the [(Ga_1.57Cr_0.03)In_0.4]O₃ phosphor showed an output power that reached 40.4 mW with a photoelectric conversion efficiency of 25% driven by a current of 60 mA, while the resulting device was able to identify damaged produce that was undetectable using visible light. These results demonstrate the outstanding potential of this phosphor for NIR LED imaging applications.

Sb-Doped Metal Halide Nanocrystals: A 0D versus 3D Comparison

We synthesize colloidal nanocrystals (NCs) of Rb₃InCl₆, composed of isolated metal halide octahedra ("0D"), and of Cs₂NaInCl₆ and Cs₂KInCl₆ double perovskites, where all octahedra share corners and are interconnected ("3D"), with the aim to elucidate and compare their optical features once doped with Sb³⁺ ions. Our optical and computational analyses evidence that the photoluminescence quantum yield (PLQY) of all these systems is consistently lower than that of the corresponding bulk materials due to the presence of deep surface traps from under-coordinated halide ions. Also, Sb-doped "0D" Rb₃InCl₆ NCs exhibit a higher PLQY than Sb-doped "3D" Cs₂NaInCl₆ and Cs₂KInCl₆ NCs, most likely because excitons responsible for the PL emission migrate to the surface faster in 3D NCs than in 0D NCs. We also observe that all these systems feature a large Stokes shift (varying from system to system), a feature that should be of interest for applications in photon management and scintillation technologies. Scintillation properties are evaluated via radioluminescence experiments, and re-absorption-free waveguiding performance in large-area plastic scintillators is assessed using Monte Carlo ray-tracing simulations.