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 <i>R</i>_a = 94, <i>R</i>9 = 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

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 <i>R</i>_a = 94, <i>R</i>9 = 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

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

Sharp-to-Broad Band Energy Transfer in Lithium Aluminate and Gallate Phosphors for SWIR LED

Short-wave infrared (SWIR) phosphor-converted light-emitting diode (LED) technology holds promise for advancing broadband light sources. Despite the potential, limited research has delved into the energy transfer mechanism from sharp-line to broadband emission in SWIR phosphors, which remains underexplored. Herein, we demonstrate bright SWIR phosphors achieved through Cr3+/Ni2+ energy transfer in LiGa5(1–x)Al5xO8. High-resolution X-ray diffraction revealed the typical solid solution and distortion occurring in Al3+ octahedral sites. In addition, the X-ray absorption spectrum illustrates that Cr3+ and Ni2+ have different coordination environments, showing the possibility that they occupy different positions or that the coordinated environment of Ni2+ is distorted due to charge imbalance. Temperature-dependent studies provide insights into the energy transfer dynamics between Cr3+/Ni2+, from the 2E level of Cr3+ (sharp band) to the 3T1 level of Ni2+ (broadband). The increased emission intensity at lower temperatures in the x = 0.6 and x = 1.0 samples can be explained by the positioning of the 3T1 level above the 2E level of Cr3+ ions. Finally, we established a mechanism involving a sharp line to broadband energy transfer showcasing a high-power SWIR LED with a radiant power of 21.45 mW

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

Correlated Na⁺ Ion Migration Invokes Zero Thermal Quenching in a Sodium Superionic Conductor-type Phosphor

Among the many potential Eu2+-activated sodium superionic conductor (NASICON)-based host materials, the Sc3+-based NASICON phosphor (Na3Sc2(PO4)3:Eu2+) is a promising phosphor material for high-power lighting applications owing to its unusual thermal stability at elevated temperatures. It has previously been shown that negative thermal quenching (TQ) can be tailored to zero TQ depending on the Eu2+ concentration. However, the obtained zero-TQ composition has low photoluminescent quantum yields, which hinders its applicability to high-power lighting. Herein, we report a holistic study of the tuning of thermal stability from negative TQ to zero TQ while preserving the original emission efficiency by introducing Lu3+ ions in Na3Sc2(PO4)3:Eu2+. Furthermore, we fabricated a high-power white light-emitting diode using optimized Lu3+-doped Na3Sc2(PO4)3:Eu2+ as the blue component, delivering a high color-rendering index value of 90 with a high luminous efficiency value of 25 lm/W obtained at a flux current of 1000 mA. Therefore, the findings of this work provide novel scientific insights into the importance of structure–property relationships in designing highly efficient thermally stable phosphors for high-power lighting applications

Photoluminescent Evolution Induced by Structural Transformation Through Thermal Treating in the Red Narrow-Band Phosphor K₂GeF₆:Mn⁴⁺

This study explored optimal preparation conditions for K₂GeF₆:Mn⁴⁺ red phosphors by using chemical coprecipitation method. The prepared hexagonal <i>P</i>3̅m1 K₂GeF₆:Mn⁴⁺ exhibited efficient red emission, high color purity, good Mn⁴⁺ concentration stability, and low thermal quenching. Structural evolution from hexagonal <i>P</i>3̅<i>m</i>1 to <i>P</i>6₃mc and then <i>P</i>6₃<i>mc</i> to cubic <i>Fm</i>3<i>m</i> occurred after thermal treatment at approximately 400 and 500 °C, respectively. Hexagonal <i>P</i>6₃mc phase showed an obvious zero phonon line peak at 621 nm, whereas cubic <i>Fm</i>3<i>m</i> phase showed no red emission. Yellowish K₂GeF₆:Mn⁴⁺ with both hexagonal <i>P</i>3̅<i>m</i>1 and <i>P</i>6₃<i>mc</i> symmetries are promising commercial red phosphors for white light-emitting diodes

Chemical Control of SrLi(Al_1–<i>x</i>Ga<i>_x</i>)₃N₄:Eu²⁺ Red Phosphors at Extreme Conditions for Application in Light-Emitting Diodes

Phosphor materials are promising candidates for white-light-emitting diode applications. High-quality phosphor materials must be synthesized under extreme conditions. In this study, a series of SrLi­(Al1–xGax)3N4:Eu2+ (GSLA) narrow-band emission red phosphors are successfully synthesized under 1000 atm nitrogen gas atmosphere through the hot isostatic press, which cannot be achieved under low pressure. Successful Ga incorporation is confirmed by X-ray diffraction and Rietveld refinement. Phonon repetition structure and detailed thermal properties are analyzed by temperature-dependent photoluminescence intensity and lifetime. The structural ordering and rigidity are comprehensively evaluated by Raman spectra. The blue shift of the photoluminescence spectra enhances the luminous efficacy of radiation, making GSLA a potential candidate for practical application. This study promotes the research on materials synthesized under extreme conditions and the development of novel phosphor materials

Probing Local Structural Changes by Sharp Luminescent Infrared Nanophosphor for Application in Light-Emitting Diodes

Cr3+-doped infrared phosphors are promising candidates for next-generation phosphor-converted infrared light-emitting diodes (LEDs) because they can, in principle, tune and convert the luminescence spectra from an LED chip. However, most studies focus on broad-band Cr3+-doped phosphors, and the control mechanism of Cr3+-doped phosphors with sharp line emissions remains ambiguous. Here, we report LiGa5(1–x)Al5xO8:Cr3+ phosphors with sharp line emissions. The luminescence analysis reveals the subtle change of the local structure around Cr3+, which cannot be well resolved by X-ray diffraction. The deviation between the temperature-dependent photoluminescence and decay profile is introduced as well. Furthermore, the morphologies of LiGa5(1–x)Al5xO8:Cr3+ phosphors with high aluminum concentration demonstrate their great potential for mini-LED applications. Finally, an LED package is constructed, and it reveals the potential for angiographic applications. This study opens up a new understanding and perspective for Cr3+-doped sharp emission phosphors and reveals their potential for LED applications