Coprecipitation Strategy for Halide-Based Solid-State Electrolytes and Atmospheric-Dependent In Situ Analysis.

In the continuous pursuit of an energy-efficient alternative to the energy-intensive mechanochemical process, we developed a coprecipitation strategy for synthesizing halide-based solid-state electrolytes that warrant both structural control and commercial scalability. In this study, we propose a new coprecipitation approach to synthesized Li3InCl6, exhibiting both structural and electrochemical performance stability, with a high ionic conductivity of 1.42 × 10-3 S cm-1, comparable to that of traditionally prepared counterparts. Through the in situ synchrotron X-ray diffraction technique, we unveil the stability mechanisms and rapid chemical reactions of Li3InCl6 under dry Ar, dry O2, and high-humidity atmosphere, which were not previously reported. Furthermore, the fast reversibility capability of moisture-exposed Li3InCl6 was tracked under vacuum, revealing the optimal recovery conditions at low temperatures (150-200 °C). This work addresses the critical challenges in structural engineering and sustainable mass production and provides insights into chemical reactions under real-world conditions.

Advancing Near-Infrared Light Sources: Enhancing Chromium Emission through Cation Substitution in Ultra-Broadband Near-Infrared Phosphors.

The growing interest in the use of near-infrared (NIR) radiation for spectroscopy, optical communication, and medical applications spanning both NIR-I (700-900 nm) and NIR-II (900-1700 nm) has driven the need for new NIR light sources. NIR phosphor-converted light-emitting diodes (pc-LEDs) are expected to replace traditional lamps mainly due to their high efficiency and compact design. Broadband NIR phosphors activated by Cr3+ and Cr4+ have attracted significant research interest, offering emission across a wide range from 700 to 1700 nm. In this work, we synthesized a series of Sc2(1-x)Ga2xO3:Cr3+/4+ materials (x = 0-0.2) with broadband NIR-I (Cr3+) and NIR-II (Cr4+) emission. We observed a substantial increase in the intensity of Cr3+ (approximately 77 times) by incorporating Ga3+ ions. Additionally, our investigation revealed that energy transfer occurred between Cr3+ and Cr4+ ions. Configuration diagrams are presented to elucidate the behavior of Cr3+ and Cr4+ ions within the Sc2O3 matrix. We also observed a phase transition at a pressure of 20.2 GPa, resulting in a new unknown phase where Cr3+ luminescence exhibited a high-symmetry environment. Notably, this study presents the pressure-induced shift of NIR Cr4+ luminescence in Sc2(1-x)Ga2xO3:Cr3+/4+. The linear shifts were estimated at 83 ± 3 and 61 ± 6 cm-1/GPa before and after the phase transition. Overall, our findings shed light on the synthesis, luminescent properties, temperature, and high-pressure behavior within the Sc2(1-x)Ga2xO3:Cr3+/4+ materials. This research contributes to the understanding and potential applications of these materials in the development of efficient NIR light sources and other optical devices.

Hidden Hexavalent Chromium Ions with Subtle Structural Evolution in Near-Infrared Phosphors.

Cr-doped inorganic materials are pivotal in developing near-infrared optical materials; however, multivalent Cr ions and their respective distribution in the materials remain ambiguous. Herein, a series of Li(Sc1-xInx)O2:Cr phosphors containing both Cr3+/Cr6+ ions are prepared. High-resolution synchrotron X-ray diffraction (XRD) reveals two similar phases in Li(Sc1-xInx)O2. Raman spectra further confirm distinct scattering patterns for the two end-member compositions, corroborating the findings from the synchrotron XRD analysis. Cr K-edge X-ray absorption near-edge structure and extended X-ray absorption fine structure demonstrate that most Cr ions in the as-prepared samples are Cr6+, while Cr3+ becomes dominant after washing with water. Moreover, the source and distribution of Cr3+ and Cr6+ ions in the as-prepared and washed samples are revealed through X-ray fluorescence and X-ray excited optical luminescence techniques, which indicate that Cr6+ ions aggregate within the sample, while Cr3+ ions are evenly distributed. Photoluminescence, decay curves, and line shape analyses are implemented to resolve the electron-lattice interactions, and the corresponding mechanisms are provided to explain the asymmetry between photoluminescence and photoluminescence excitation spectra. Overall, this study provides valuable insights into the distribution of low-concentration multivalence ions in solid-state materials and offers a deeper understanding of the approaches to precisely resolve the subtle changes in the crystal structure.

Highly Active NiO-Ni(OH)2 -Cr2 O3 /Ni Hydrogen Evolution Electrocatalyst through Synergistic Reaction Kinetics.

High activity catalysts for hydrogen evolution reaction (HER) play a key role in converting renewable electricity to storable hydrogen fuel. Great effort has been devoted to the search for noble metal free catalysts to make electrolysis viable for practical applications. Here, a non-precious metal oxide/metal catalyst with high intrinsic activity comparable to Pt/C was reported. The electrocatalyst consisting of NiO, Ni(OH)2 , Cr2 O3 , and Ni metal exhibits a low overpotential of 27, 103, and 153 mV at current densities of 10, 100, and 200 mA cm-2 , respectively, in a 1.0 m NaOH electrolyte. The activity is much higher than that of NiOx /Ni or Cr2 O3 alone, showing the synergistic effect of NiOx /Ni and Cr2 O3 on catalyzing HER. Density functional theory calculations shows that NiO and Cr2 O3 on Ni surface lower the disassociation energy barrier for breaking H-OH bond, while Ni(OH)2 and Cr2 O3 create preferred sites on Ni surface with near-zero H* adsorption free energy to promote H* to gaseous H2 evolution. These synergistic effects of multiple-oxides/metal composition enhance the disassociation of H-OH and the evolution of H* to gaseous H2 , thus achieving high activity and demonstrating a promising composition design for noble metal free catalyst.

Quantum Dot-Vitrimer Composites: An Approach for Reprocessable, Self-Healable, and Sustainable Luminescent Materials.

Quantum dots (QDs) are of great concern in many fields. However, they suffer from high toxicity and may lead to environmental pollution. We report the development of a QD-vitrimer composite with reprocessable, self-healable, and sustainable properties. Our QD-vitrimer composite reveals fine transparency and highly uniform QDs distribution without significant aggregation. The photoluminescence quantum yield (PLQY) is basically about four times higher than the commercial QD films. The QD-vitrimer composites can be recycled at least three times without any significant loss in structure and luminescence efficiency. A prototype light-emitting diode device is fabricated to demonstrate the promising potential of QD-vitrimer composites in real application. This research sheds light on developing environmentally friendly luminescent materials and opens up an avenue for designing advanced nanomaterials-vitrimer composites.

Evolutionary Generation of Phosphor Materials and Their Progress in Future Applications for Light-Emitting Diodes.

Light-emitting diodes (LEDs) are attracting considerable attention around the world. Phosphor materials, as crucial color-converted components, play central roles in LED development. The demands for phosphor materials have become increasingly stringent over the past decades, from high brightness to narrowband emission or function-dependent spectrum engineering. Although substantial progress has been made for currently developed phosphor materials, simultaneously satisfying all requirements for high-level applications remains challenging. In this review, we aim to provide a comprehensive understanding of the development of phosphor materials in different generations and to elucidate the key designed mechanisms concerning the activators and the host structures to fulfill the aforementioned aspects. We highlight the developments in phosphor materials through the classification of demands for high luminescence, high thermal stability, narrowband emission for high color gamut, and broadband emission for near-infrared. We also focus on elucidating the key designed mechanisms of phosphor materials in different generations. Furthermore, future perspectives about micro-LED applications and nanoluminescent materials are provided. This study opens up an avenue for designing the luminescent materials of the future.

Chromium Ion Pair Luminescence: A Strategy in Broadband Near-Infrared Light-Emitting Diode Design.

Portable near-infrared (NIR) light sources are in high demand for applications in spectroscopy, night vision, bioimaging, and many others. Typical phosphor designs feature isolated Cr3+ ion centers, and it is challenging to design broadband NIR phosphors based on Cr3+-Cr3+ pairs. Here, we explore the solid-solution series SrAl11.88-xGaxO19:0.12Cr3+ (x = 0, 2, 4, 6, 8, 10, and 12) as phosphors featuring Cr3+-Cr3+ pairs and evaluate structure-property relations within the series. We establish the incorporation of Ga within the magentoplumbite-type structure at five distinct crystallographic sites and evaluate the effect of this incorporation on the Cr3+-Cr3+ ion pair proximity. Electron paramagnetic measurements reveal the presence of both isolated Cr3+ and Cr3+-Cr3+ pairs, resulting in NIR luminescence at approximately 650-1050 nm. Unexpectedly, the origin of broadband NIR luminescence with a peak within the range 740-820 nm is related to the Cr3+-Cr3+ ion pair. We demonstrate the application of the SrAl5.88Ga6O19:0.12Cr3+ phosphor, which possesses an internal quantum efficiency of ∼85%, a radiant flux of ∼95 mW, and zero thermal quenching up to 500 K. This work provides a further understanding of spectral shifts in phosphor solid solutions and in particular the application of the magentoplumbites as promising next-generation NIR phosphor host systems.

Formation and Near-Infrared Emission of CsPbI3 Nanoparticles Embedded in Cs4PbI6 Crystals.

Cs4PbI6, as a rarely investigated member of the Cs4PbX6 (X is a halogen element) family, has been successfully synthesized at low temperatures, and the synthetic conditions have been optimized. Metal iodides such as LiI, KI, NiI2, CoI2, and ZnI2, as additives, play an important role in enhancing the formation of the Cs4PbI6 microcrystals. ZnI2 with the lowest dissociation energy is the most efficient additive to supply iodide ions, and its amount of addition has also been optimized. Strong red to near-infrared (NIR) emission properties have been detected, and its optical emission centers have been identified to be numerous embedded perovskite-type α-CsPbI3 nanocrystallites (∼5 nm in diameter) based on investigations of temperature- and pressure-dependent photoluminescent properties. High-resolution transmission electron microscopy was used to detect these hidden nanoparticles, although the material was highly beam-sensitive and confirmed a "raisin bread"-like structure of the Cs4PbI6 crystals. A NIR mini-LED for the biological application has been successfully fabricated using as-synthesized Cs4PbI6 crystals. This work provides information for the future development of infrared fluorescent nanoscale perovskite materials.

Multi-Site Cation Control of Ultra-Broadband Near-Infrared Phosphors for Application in Light-Emitting Diodes.

Near-infrared (NIR) phosphors are fascinating materials that have numerous applications in diverse fields. In this study, a series of La3Ga5GeO14:Cr3+ phosphors, which was incorporated with Sn4+, Ba2+, and Sc3+, was successfully synthesized using solid-state reaction to explore every cationic site comprehensively. The crystal structures were well resolved by combining synchrotron X-ray diffraction and neutron powder diffraction through joint Rietveld refinements. The trapping of free electrons induced by charge unbalances and lattice vacancies changes the magnetic properties, which was well explained by a Dyson curve in electron paramagnetic resonance. Temperature and pressure-dependent photoluminescence spectra reveal various luminescent properties between strong and weak fields in different dopant centers. The phosphor-converted NIR light-emitting diode (pc-NIR LED) package demonstrates a superior broadband emission that covers the near-infrared (NIR) region of 650-1050 nm. This study can provide researchers with new insight into the control mechanism of multiple-cation-site phosphors and reveal a potential phosphor candidate for practical NIR LED application.

Broadband NaK2Li[Li3SiO4]4:Ce Alkali Lithosilicate Blue Phosphors.

Phosphors with a rigid and symmetrical structure are urgently needed. The alkali lithosilicate family (A[Li3SiO4]) has been extensively studied with a narrow emission band due to its unique cuboid-coordinated environment and rigid structure. However, here we demonstrate for the first time Ce-doped NaK2Li[Li3SiO4]4 phosphors with a broad emission band, a high internal quantum efficiency (85.6%), and excellent thermal stability. Photoluminescence indicates the Ce's preference to occupy the Na+ site, leading to a strong blue color emission with peak maxima at 417 and 450 nm. Temperature- and pressure-dependent photoluminescence reveals thermal stability and a phase transition. Moreover, the X-ray absorption near-edge structure reveals the mixing of Ce3+ and Ce4+ in the materials; this result differs from that of Eu2+-doped A[Li3SiO4] phosphors. The charge compensation process is then proposed to explain this difference. This study not only provides insights into Ce-doped UCr4C4-type phosphors but also explains the charge compensation mechanism of the aliovalent doping process.

Chromium(III)-Doped Fluoride Phosphors with Broadband Infrared Emission for Light-Emitting Diodes.

Two types of infrared fluoride phosphors, Cr3+-doped K3AlF6 and K3GaF6, were developed in this research. The K3Al1-xF6:xCr3+ and K3Ga1-yF6:yCr3+ fluoride phosphors were proven to be pure phase via X-ray diffraction refinement, which demonstrated that the procedure can be applied to large-scale production. Electron paramagnetic resonance measurements indicated that Cr3+ ions in cubic with respect to noncubic are coupled better with K3GaF6 than with K3AlF6. The main differences between these two phosphors, the site symmetry and pressure behavior of the spectra, were obtained in temperature- and pressure-dependent spectra. According to the calculation results, Cr3+ in fluorine coordination at ambient pressure indicates an intermediate crystal field. For the phosphor-converted light-emitting diodes (LEDs) fabricated from these two phosphors, the spectral range is from 650 to 1000 nm, which resulted in a radiant flux of 7-8 mW with an input power of 1.05 W. The research reveals detailed luminous properties, which will lead to a new way of studying Cr3+-doped fluoride phosphors and their application in LEDs.

Recent Developments in Lead-Free Double Perovskites: Structure, Doping, and Applications.

Lead-free perovskite structures have been recently attracting considerable attention because of their eco-friendly nature and properties, such as their lead-based structure. In this work, we reviewed the lead-free double perovskite (LFDP) structure because of its unique electronic dimensions, chemical stability, and substitutional chemistry compared with other lead-free structures. We highlighted the recent progress on crystal structure prediction, synthesis methods, metal dopants, and ligand passivation on LFDPs. LFDPs are useful for several applications, such as solar cells, light-emitting diodes, degradation of photocatalytic dyes, sensors, and X-ray detectors. This report provides a summary of recent progress as a reference for further research on lead-free perovskite structures.

Structural Evolution and Effect of the Neighboring Cation on the Photoluminescence of Sr(LiAl3 )1-x (SiMg3 )x N4 :Eu2+ Phosphors.

In this study, a series of Sr(LiAl3 )1-x (SiMg3 )x N4 :Eu2+ (SLA-SSM) phosphors were synthesized by a solid-solution process. The emission peak maxima of SLA-SSM range from 615 nm to 680 nm, which indicates structural differences in these materials. 7 Li solid-state NMR spectroscopy was utilized to distinguish between the Li(1)N4 and Li(2)N4 tetrahedra in SLA-SSM. Differences in the coordination environments of the two Sr sites were found which explain the unexpected luminescent properties. Three discernible morphologies were detected by scanning electron microscopy. Temperature-dependent photoluminescence and decay times were used to understand the diverse environments of europium ions in the two strontium sites Sr1 and Sr2, which also support the NMR analysis. Moreover, X-ray absorption near-edge structure studies reveal that the Eu2+ concentration in SLA-SSM is much higher than that in in SrLiAl3 N4 :Eu2+ and SrSiMg3 N4 :Eu2+ phosphors. Finally, an overall mechanism was proposed to explain the how the change in photoluminescence is controlled by the size of the coordinated cation.

Integrated Surface Modification to Enhance the Luminescence Properties of K2TiF6:Mn4+ Phosphor and Its Application in White-Light-Emitting Diodes.

Narrow-band Mn4+-doped fluoride phosphors have become a research hotspot worldwide. In this study, we propose integrated surface modification processes to enhance the performance and stability of the luminescence properties of K2TiF6:Mn4+ (KTF) phosphor. These integrated process are applied in the initial synthesis step, coating of the as-synthesized powder post-treatment process, and during the application of the phosphor in the white-light-emitting diode (WLED) device. Surface etching is conducted to remove impurities and small particles in KTF. Double-shell coating forms a stable protective layer outside the KTF. Atomic layer deposition is employed for the surface of the WLED device.

Ultrafast Self-Crystallization of High-External-Quantum-Efficient Fluoride Phosphors for Warm White Light-Emitting Diodes.

In this study, we used HF (as good solvent) to dissolve K2GeF6 and K2MnF6 and added ethanol (as poor solvent) to cause ultrafast self-crystallization of K2GeF6:Mn4+ crystals, which had an unprecedentedly high external quantum efficiency that reached 73%. By using the red phosphor, we achieved a high-quality warm white light-emitting diode with color-rendering index of Ra = 94, R9 = 95, luminous efficacy of 150 lm W-1, and correlated color temperature at 3652 K. Furthermore, the good-poor solvent strategy can be used to fast synthesize other fluorides.

Control of Luminescence by Tuning of Crystal Symmetry and Local Structure in Mn4+ -Activated Narrow Band Fluoride Phosphors.

Mn4+ -doped fluoride phosphors have been widely used in wide-gamut backlighting devices because of their extremely narrow emission band. Solid solutions of Na2 (Six Ge1-x )F6 :Mn4+ and Na2 (Gey Ti1-y )F6 :Mn4+ were successfully synthesized to elucidate the behavior of the zero-phonon line (ZPL) in different structures. The ratio between ZPL and the highest emission intensity υ6 phonon sideband exhibits a strong relationship with luminescent decay rate. First-principles calculations are conducted to model the variation in the structural and electronic properties of the prepared solid solutions as a function of the composition. To compensate for the limitations of the Rietveld refinement, electron paramagnetic resonance and high-resolution steady-state emission spectra are used to confirm the diverse local environment for Mn4+ in the structure. Finally, the spectral luminous efficacy of radiation (LER) is used to reveal the important role of ZPL in practical applications.

Enhanced Photoluminescence Emission and Thermal Stability from Introduced Cation Disorder in Phosphors.

Optimizing properties of phosphors for use in white-light-emitting diodes (WLEDs) is an important materials challenge. Most phosphors have a low level of lattice disorder due to mismatch between the host and activator cations. Here we show that deliberate introduction of high levels of cation disorder leads to significant improvements in quantum efficiency, stability to thermal quenching, and emission lifetime in Sr1.98-x(Ca0.55Ba0.45)xSi5N8:Eu0.02 (x = 0-1.5) phosphors. Replacing Sr by a (Ca0.55Ba0.45) mixture with the same average radius increases cation size variance, resulting in photoluminescence emission increases of 20-26% for the x = 1.5 sample relative to the x = 0 parent across the 25-200 °C range that spans WLED working temperatures. Cation disorder suppresses nonradiative processes through disruption of lattice vibrations and creates deep traps that release electrons to compensate for thermal quenching. Introduction of high levels of cation disorder may thus be a very useful general approach for improving the efficiency of luminescent materials.

Aluminate Red Phosphor in Light-Emitting Diodes: Theoretical Calculations, Charge Varieties, and High-Pressure Luminescence Analysis.

Searching for a non-rare-earth-based oxide red-emitting phosphor is crucial for phosphor-converted light-emitting diodes (LEDs). In this study, we optimized a blue and UV-light excited Sr4Al14O25:Mn phosphor exhibiting red emission peaked at ∼653 nm, which was successfully synthesized by solid-state reaction. The crystal structure, micromorphology, and luminescent properties of Sr4Al14O25:Mn phosphors were characterized by X-ray Rietveld refinement, high-resolution transmission electron microscopy, and photoluminescence spectra. The band gap and electronic structure of Sr4Al14O25 were analyzed by density functional theory calculations using the hybrid exchange-correlation functional. The crystal field environment effect of Al sites from introducing activator Mn ions was investigated with the aid of Raman 27Al nuclear magnetic resonance spectra and electron spin resonance. The pressure dependent luminescent properties and decay time of this compound were presented. The tricolor display spectrum by combining blue InGaN chips, commercial ß-SiAlON:Eu2+ green phosphor, and Sr4Al14O25:Mn red phosphor were evaluated for commercial applications: using the present Sr4Al14O25:Mn red phosphor converted LED as a backlighting source.

Enhance Color Rendering Index via Full Spectrum Employing the Important Key of Cyan Phosphor.

A new concept called "full-spectrum lighting" has attracted considerable attention in recent years. Traditional devices are usually combined with ultraviolet-light-emitting diode (LED), red, green, and blue phosphors. However, a cyan cavity exists in the 480-520 nm region. Hence, cyan phosphors are needed to compensate for the cavity. (Sr,Ba)5(PO4)3Cl:Eu2+ phosphors feature an extremely unique and tunable photoluminescence spectrum. Nevertheless, the tuning mechanisms of these phosphors remain unclear. In this study, we elucidate the mechanism of the cation size-controlled activator uneven-occupation and reoxidation in (Sr,Ba)5(PO4)3Cl:Eu2+ phosphors. This mechanism could help tune the optical properties of related apatite families and structures with multiple cation sites and strongly uneven occupation of activators and cations. Finally, the package of the LED device is constructed to show that both color rendering index Ra and R9 are higher than 95. Thus, the device could be a potential candidate for full-spectrum lighting.

Narrow Red Emission Band Fluoride Phosphor KNaSiF6:Mn(4+) for Warm White Light-Emitting Diodes.

Red phosphors AMF6:Mn(4+) (A = Na, K, Cs, Ba, Rb; M = Si, Ti, Ge) have been widely studied due to the narrow red emission bands around 630 nm. The different emission of the zero-phonon line (ZPL) may affect the color rendering index of white light-emitting diodes (WLED). The primary reason behind the emergence and intensity of ZPL, taking KNaSiF6:Mn(4+) as an example, was investigated here. The effects of pressure on crystal structure and luminescence were determined experimentally and theoretically. The increase of band gap, red shift of emission spectrum and blue shift of excitation spectrum were observed with higher applied pressure. The angles of ∠FMnF and ∠FMF(M = Si, Ti, Ge) were found clearly distorted from 180° in MF6(2-) octahedron with strong ZPL intensity. The larger distorted SiF6(2-) octahedron, the stronger ZPL intensity. This research provides a new perspective to address the ZPL intensity problem of the hexafluorosilicate phosphors caused by crystal distortion and pressure-dependence of the luminescence. The efficacy of the device featuring from Y3Al5O12:Ce(3+) (YAG) and KNaSiF6:Mn(4+) phosphor was 118 lm/W with the color temperature of 3455 K. These results reveal that KNaSiF6:Mn(4+) presents good luminescent properties and could be a potential candidate material for application in back-lighting systems.