YAG:Ce3+ Transparent Ceramic Phosphors Brighten the Next-Generation Laser-Driven Lighting

Generated White Light Having Adaptable Chromaticity and Emission, Using Spectrally Reconfigurable Microcavities

Metal-free, luminescent, carbogenic nanomaterials (LCNMs) constitute a novel class of optical materials with low environmental impact. LCNMs, e.g., carbon dots (CDs), graphitic carbon nitride (g-C3N4), and carbonized polymer microspheres (CPM) show strong blue/cyan emissions, but rather weak yellow/red emission. This has been a serious drawback in applying them to light-emitting and bio-imaging applications. Here, by integrating single-component LCNMs in photonic microcavities, the study spectroscopically engineers the coupling between photonic modes in these microcavities and optical transitions to "reconfigure" the emission spectra of these luminescent materials. Resonant photons are confined in the microcavity, which allows selective re-excitation of phosphors to effectively emit down-converted photons. The down-converted photons re-excite the phosphors and are multiply recycled, leading to enhanced yellow/red emissions and resulting in white-light emission (WLE). Furthermore, by adjusting photonic stop bands of microcavity components, color adaptable (cool, pure, and warm) WLE is flexibly generated, which precisely follows the black-body Planckian locus in the chromaticity diagram. The proposed approach offers practical low-cost chromaticity-adjustable WLE from single-component, luminescent materials without any chemical or surface modification, or elaborate machinery and processing, paving the way for practical WLE devices.

Smart Window with Reversible and Instantaneous Photoluminescence based on Microsphere Structure

A smart window that dynamically regulates light transmittance is crucial for modern life end-users and promising for on-demand optical devices. The advent of three-dimensional (3D) photonic crystal microspheres has enriched the functions of a smart window. However, the smart window formed by polymer microspheres encounters poor mechanical strength and microstructural defects. Herein, to solve this limitation, we report the microsphere-based smart window composed of tightly packed cross-linked polymer microspheres (as a precursor) containing organic photochromic dyes, followed by compression under a high elastic state. When excited under an ultraviolet supply, our smart window showed a rapid and reversible fluorescent photoluminescence without fatigue (50 cycles). Moreover, the bulk devices with a microsphere cross-linked network structure enable excellent mechanical strength (hardness reached 0.158 GPa) and visible-light transparency. Interestingly, a QR code can be recognized under visible light exposure but not under ultraviolet light exposure because of photoluminescence of the smart window. Our method generally provided a paradigm for various amorphous polymers, which can be regarded as a simple and effective approach to build a versatile strategy to introduce an ideal marketplace with economic and community benefits.

Wide Range Near-Zero Thermal Quenching of Orange-Yellow Phosphor via Impeding Self-Oxidation of Eu2+ for Versatile Optoelectronic Applications

Li2SrSiO4:Eu2+ is a promising substitute for traditional Y3Al5O12:Ce3+ (YAG:Ce3+) owing to its strong orange-yellow emission of 4f-5d transition originating from Eu2+ dopant, covering the more red-light region. However, its inevitable luminescence thermal quenching at high temperatures and the self-oxidation of Eu2+ strongly impede their applications. Their remediation remains highly challenging. Herein, an anti-self-oxidation(ASO) concept of Eu2+ in Li2SrSiO4 substrate by adding trivalent rare-earth ions (A3+: A = La, Gd, Y, Lu) for highly efficient and stable orange-yellow light emission have been proposed. A significantly increased orange-yellow emission (202% improvement) from Li2Sr0.95A0.05SiO4:Eu2+ with a wide range near-zero thermal quenching is obtained, superior to other Eu2+ activated phosphors. The presence of A3+ ions with various radii modifies the ASO degree of Eu2+ ions, achieving the tunable chemical state, composition, electronic configuration, crystal-field strength, and luminescent characteristics of the developed phosphors. For the proof of the concept, a W-LED device and a PDMS (Polydimethylsiloxane) luminescent film are fabricated, endowing excellent luminescence performance and thermal stability and the huge application prospects of Li2SrSiO4:Eu2+ in lighting and display fields.

A Novel PiGF@Diamond Color Converter with a Record Thermal Conductivity for Laser-Driven Projection Display

High-brightness laser lighting is confronted with crucial challenges in developing laser-excitable color converting materials with effective heat dissipation and super optical performance. Herein, a novel composite of phosphor-in-glass film on transparent diamond (PiGF@diamond) is designed and fabricated via a facile low-temperature co-sintering strategy. The as-prepared La3Si6N11:Ce3+ (LSN:Ce) PiGF@diamond with well-retained optical properties of raw phosphor shows a record thermal conductivity of ≈599 W m-1 K-1, which is about 60 times higher than that of currently well-used PiGF@sapphire (≈10 W m-1 K-1). As a consequence, this color converter can bear laser power density up to 40.24 W mm-2 and a maximum luminance flux of 5602 lm without luminescence saturation due to efficient inhibition of laser-induced heat accumulation. By further supplementing red spectral component of CaAlSiN3:Eu2+ (CASN:Eu), the PiGF@diamond based white laser diode is successfully constructed, which can yield warm white light with a high color rendering index of 89.3 and find practical LD-driven applications. The findings will pave the way for realizing the commercial application of PiGF composite in laser lighting and display.

Rational Design of Nitride Phosphor-In-Glass with Robust Stability and Photoluminescence Performance

Phosphor-in-glass represents a promising avenue for merging the luminous efficiency of high-quality phosphor and the thermal stability of a glass matrix. Undoubtedly, the glass matrix system and its preparation are pivotal factors in achieving high stability and preserving the original performance of embedded phosphor particles. In contrast to the well-established commercial Y3Al5O12:Ce3+ oxide phosphor, red nitride phosphor, which plays a critical role in high-quality lighting, exhibits greater structural instability during the high-temperature synthesis of inorganic glasses. A telluride glass with a refractive index (RI = 2.15@615 nm) akin to that of nitride phosphor (∼2.19) has been devised, demonstrating high efficiency in photon utilization. The lower glass-transition temperature plays a crucial role in safeguarding phosphor particles against erosion resulting from exposure to high-temperature melts. Phosphor-in-glass retains 93% of the quantum efficiency observed for pure phosphor. The assembled white light-emitting diodes module has precise color tuning capabilities, achieving an optimal color rendering index of 93.7, a luminous efficacy of 80.4 lm/W, and a correlated color temperature of 5850 K. These outcomes hold potential for advancing the realm of inorganic package and high-quality white light illumination.

Study on a Highly Thermostable Dy3+-Activated Borophosphate Phosphor

Constructing a phosphor with multifunctional applications is an imperative challenge. Especially, highly thermostable luminescence of phosphor is indispensable for stable white-light-emitting diodes (LEDs). Nevertheless, good thermal quenching resistance behavior is unfavorable for a fluorescence intensity ratio (FIR)-based optical temperature sensor. Herein, a highly thermostable Ba3(ZnB5O10)PO4 (BZBP)-based phosphor is successfully achieved via replacing Ba2+ with Dy3+, demonstrating simultaneously promising lighting and thermometry utilizations. Under the excitation of 350 nm, the title phosphor only loses 12% of the initial intensity when the temperature is up to 473 K, ensuring sufficient luminescence thermostability for white-LED lighting. The white-LED device fabricated using the title phosphor emits high-quality white light with a high color rendering index (Ra = 93) and low correlated color temperature (CCT = 3996 K). Meanwhile, the yellow and blue emission intensities demonstrate a downtrend difference with rising temperature. Temperature sensing properties are assessed through FIR technology. The maximal relative sensitivity reaches as high as 0.0379 K-1 at 298 K. These results reveal that the title phosphor has a great potential for indoor lighting and thermometry applications.

Characterization of Sm3+-activated carbonated calcium chlorapatite phosphors for theranostic applications: a comparative study of co-precipitation and hydrothermal methods

Continuous efforts are ongoing to discover new luminescent materials with appropriate properties for applications in medicine, serving as theranostic agents for healing and bioimaging. In this paper, novel single-phase carbonated calcium chlorapatite (Ca10(PO4)5(CO3)Cl2, abbreviated as CaClAp-CO3) phosphors activated with varying concentrations of Sm3+ ions were successfully fabricated using both co-precipitation and hydrothermal methods to investigate the influence of the synthesis techniques on the physicochemical properties of these materials. The effects of doping concentration of Sm3+ ions and synthesis techniques on the structure, photoluminescence (PL), energy transfer, substitute sites, fluorescence lifetime and luminescence colour of phosphors were investigated. The synthesized phosphors were characterized by X-ray diffraction (XRD) to confirm their crystal phase structure and purity. Vibrational features and the incorporation of carbonate ions were verified using Fourier-transform infrared (FTIR) spectroscopy. The obtained materials emit reddish-orange light, primarily from the most intense 4G5/2 → 6H7/2 transition. The electric dipole to magnetic dipole transition ratio (ED/MD), CIE colour coordinates and colour purity were determined to provide additional insights into the spectroscopic attributes of the obtained phosphors. In addition, the concentration quenching was also observed, and its mechanism was proposed based on theoretical calculations showing the multipolar interactions.

Development of dual-channel fluorescent mesoporous SiO2 nanosphere-coated yttrium aluminum garnet composites for sensitive detection of latent fingerprints

In this study, we investigated the detection of latent fingerprints (LFPs) using green light- and near-infrared (NIR) light-induced up/down-conversion dual-channel composites. Upconverted yttrium aluminium garnet (YAG) was prepared using a citric acid-assisted sol-gel method. After loading rhodamine 6G (RhD-6) into mesoporous silica nanospheres (MSNs), the MSNs-RhD-6 composites were coated with the as-synthesised YAG via electrostatic adsorption using the layer-by-layer method, demonstrating reversible switching between yellow and green light waves under 525 nm green light or 980 nm laser excitation. To evaluate the effectiveness of YAG-MSNs-RhD-6 powder in criminal investigations, we conducted simulations for different fingerprint scenarios. The results indicated that even after prolonged aging (up to 20 days), exposure to water, or high-temperature baking, the fingerprints remained clearly visible in the images. The detection of LFPs on various substrate surfaces exhibited high contrast, with the details of the fingerprints easily observable even after appropriate magnification. This study opens a new path for green light- and near-infrared light-induced up/down-conversion dual-channel composites for optical applications.

Thermally Stable Red-Emitting Ca18K3Sc(PO4)14:Mn2+ Phosphor and Enhanced Luminescence by Energy Transfer Between Ce3+-Eu2+-Mn2

It is significant and valuable to investigate novel and high-performance red-emitting phosphors for high-quality wLED applications. Based on this consideration, we developed a novel Mn2+-doped red Ca18K3Sc(PO4)14:Mn2+ (CKSP:Mn2+) phosphor. The emission peak of CKSP:Mn2+ is located at 640 nm, presenting a broadband red emission with a fwhm of 79 nm under 405 nm excitation. The CKSP:1.0Mn2+ phosphor shows superior thermal stability. At 150 °C, the integrated PL intensity and peak intensity of the CKSP:1.0Mn2+ phosphor maintain 93.2 and 85.7% of those at 25 °C, respectively. Through the strategy of energy transfer among Ce3+-Eu2+-Mn2+, the PL intensity of Mn2+ has increased by nearly 118 times, and the quantum yield has improved from 6 up to 72%. The structure-related photoluminescence and energy transfer mechanisms are discussed in detail. The as-fabricated wLED pumped by a 370 nm LED chip combining commercial the green (Sr,Ba)2SiO4:Eu2+ phosphor, blue BaMgAl10O17:Eu2+ phosphor, and the as-synthesized CKSP:1.0Mn2+, 0.02Eu2+, 0.40Ce3+ phosphor shows excellent color quality (CCT = 5555 K, Ra = 87), which indicates that the CKSP:1.0Mn2+, 0.02Eu2+, 0.40Ce3+ phosphor has extraordinary broad prospects in future wLED applications.

Rapid synthesis of phosphor-glass composites in seconds based on particle self-stabilization

Phosphor-glass composites (PGC) are excellent candidates for highly efficient and stable photonic converters; however, their synthesis generally requires harsh procedures and long time, resulting in additional performance loss and energy consumption. Here we develop a rapid synthetic route to PGC within about 10 seconds, which enables uniform dispersion of Y3Al5O12:Ce3+ (YAG:Ce) phosphor particles through a particle self-stabilization model in molten tellurite glass. Thanks for good wettability between YAG:Ce micro-particles and tellurite glass melt, it creates an energy barrier of 6.94 × 105 zJ to prevent atomic-scale contact and sintering of particles in the melt. This in turn allows the generation of YAG:Ce-based PGC as attractive emitters with high quantum efficiency (98.4%) and absorption coefficient (86.8%) that can produce bright white light with luminous flux of 1227 lm and luminous efficiency of 276 lm W-1 under blue laser driving. This work shows a generalizable synthetic strategy for the development of functional glass composites.

High luminous efficiency and high saturation threshold in highly transparent LuAG:Ce phosphor ceramics for laser diodes lighting

Lu3Al5O12:Ce (LuAG:Ce) phosphor ceramics (PCs) with the excellent thermal stability and high saturation threshold are considered as the best green-fluorescent converters for high-power laser diodes (LDs) lighting. In this study, the effects of sintering additives and sintering processes on the transmittance and microstructure of LuAG:Ce PCs were systematically studied, and the luminescence performance of ceramics with different transmittance was compared. LuAG:Ce PCs with the transmittance of 80% (@800 nm, 1.5 mm) were obtained by using 0.1 wt.% MgO and 0.5 wt.% TEOS as sintering additives, combined with optimized vacuum pre-sintering and hot isostatic pressing. Compared to the non-HIP samples, the transmittance had increased by 11%. The microstructure of ceramics indicated that high transparency was closely related to the decrease in intergranular pores. Notably, the luminous efficiency of 253 lm/W and its saturation thresholds of > 46 W/mm2 were obtained simultaneously in green-emitting LDs devices. Moreover, under 3W laser irradiation, highly transparent ceramics had the low surface temperature of 66.4 °C, indicating the good heat dissipation performance. The observed high luminous efficiency and high saturation threshold of LuAG:Ce PCs were attributed to fewer pores and oxygen vacancies. Therefore, this work proves that highly transparent LuAG:Ce PCs are promising green-fluorescent converters for high-power LDs lighting.

High luminous efficiency and excellent thermal performance in rod-shaped YAG:Ce phosphor ceramics for laser lighting

High power and high brightness laser lighting puts forward new requirements for phosphor converters such as high luminous efficiency, high thermal conductivity and high saturation threshold due to the severe thermal effect. The structure design of phosphor converters is proposed as what we believe to be a novel strategy for less heat production and more heat conduction. In this work, the rod-shaped YAG:Ce phosphor ceramics (PCs) and disc-shaped YAG:Ce PCs as control group were fabricated by the gel casting and vacuum sintering, to comparatively study the luminescence performance for LD lighting, on the premise that the total number of transverse Ce3+ ions and the volume of samples from two comparison groups were same. All rod YAG:Ce PCs with low Ce3+ concentration exhibited the high luminous efficiency and better thermal stability than YAG:Ce discs with high Ce3+ concentration. Under the laser power density of 47.8 W/mm2, the luminous saturation was never observed in all rod-shaped YAG:Ce PCs. The high luminous efficacy of 245∼274 lm/W, CRI of 56.3∼59.5 and CCT of 4509∼4478 K were achieved. More importantly, due to the extremely low Ce3+ doping concentration (0.01 at%), rod-shaped ceramics based LDs devices showed the excellent thermal performance and their surface temperatures were even below 30.5 °C surprisingly under the laser power density of 20.3 W·mm-2 (2 W). These results indicate that the rod shape of phosphor converter is a promising structure engineering for high power laser lighting.

Synthesis and investigation of novel boron- and magnesium-doped YAG:Ce and LuAG:Ce phosphor ceramics

YAG:Ce and LuAG:Ce ceramics are widely used as scintillator materials that convert high-energy radiation into visible light. For the practical application of such compounds, short decay times are a necessity. One way of shortening the existing decay times even more is to change the local environment of emitting ions by means of doping the matrix with additional elements, for example, boron or magnesium. Furthermore, boron ions also can help absorb gamma rays more efficiently, therefore improving overall applicability. Due to the aforementioned reasons, YAG and LuAG ceramics doped with cerium, boron, and magnesium were synthesized. Initial amorphous powders have been obtained by means of sol-gel synthesis and pressed into pellets under isostatic pressure and finally calcinated to form crystalline ceramics. The effects of boron and magnesium doping on the morphological, structural, and luminescence properties were investigated. The key results showed that doping with boron has indeed shortened the decay times of the garnet pellets. Overall, boron doping of ceramics is a relatively new research area; however, it is rather promising as it helps both to improve the luminescence properties and to increase particle growth rate.

Energy transfer and tunable emission in BaSrGd4O8:Bi3+,Eu3+ phosphors for warm WLED

In this work, a series of BaSrGd4O8:xBi3+ blue phosphors was synthesized employing the high-temperature solid-state method. Phase purity of the samples was verified by X-ray diffraction and Rietveld refinement. Time-resolved photoluminescence spectra revealed the existence of two distinct Bi sites. Subsequent optimization of dopant types and doping levels in the batch led to an almost twofold increase in quantum efficiency. The introduction of Eu3+ into the phosphors facilitated the construction of an energy transfer pathway. As the concentration of Eu3+ was increased, the emission color changed from blue to purple and finally to red. In addition, the thermal stability and potential applications of the phosphors were extensively investigated. Finally, two WLED devices were successfully fabricated with color rendering indices of 96.27 and 92.18, and correlated color temperatures of 5198 and 2475 K. This underscores the prospective application of these phosphors in the field of high-quality warm WLEDs.

All-inorganic color converter based on a phosphor in bismuthate glass for white laser diode lighting

Blue laser diodes (LDs) combined with phosphors have been recognized as the next-generation solid white lighting technology. The phosphor-in-glass (PiG) coating is used for packaging as an appropriate fluorescent conversion material applied to white light LDs. In this work, a low melting point glass Bi2O3-B2O3-ZnO-BaO (BiBZBa), which was mixed with YAG:Ce3+ phosphor powder, was selected as a glass matrix, and the coating of the phosphor in bismuthate glass (PiBG) was successfully fabricated on different substrates through multilayer screen-printing and low-temperature sintering processes. The PiBG-coated substrates were integrated with a 440 nm LD chip in different interlayer structures to obtain PiBG-packaged white laser diodes (WLDs). The thermal performance of Bi2O3-B2O3-ZnO-BaO glass and the phase composition, microstructure, and luminescence properties of PiBG coatings were studied, and the optical performances of WLDs were investigated. When the reflective WLDs were excited by a blue laser with a laser power density of up to 9.3 W mm-2, the related luminous flux (LF), luminous efficiency (LE), and chromaticity coordinates were 3091 lm, 103 lm W-1, and (0.32, 0.32), respectively, indicating great potential in PiBG-packaged high power laser lighting applications.

Concentration quenching inhibition and fluorescence enhancement in Eu3+-doped molybdate red phosphors with two-phase mixing

Red phosphor plays a crucial role in improving the quality of white light illumination and backlight displays. However, significant challenges remain to enhance red emission intensity in different matrix materials. Herein, a class of two-phase mixing red phosphors of NaIn1-x(MoO4)2:xEu3+ (NIMO:xEu3+) has been successfully prepared by the traditional high-temperature solid-state reaction method. The coordination environment, phase structure, excitation and emission spectra, fluorescence kinetics, and temperature-dependent luminescence properties of the system have been studied comprehensively. It is worth mentioning that the red emission intensity continues to increase with the increased Eu3+ doping concentration, and the fluorescence lifetimes remain unchanged. These extraordinary phenomena mainly stem from the special concentration quenching mechanism in such two-phase mixing material, namely, the increased lattice interface barriers from Eu six-coordinated units and Eu eight-coordinated units can effectively block the non-radiation by enlarging the average distance between luminescent centers. The improved fluorescence thermal stability and suppressed non-radiative transition rate in NIMO:40%Eu3+ sample are further proving regulatory role of lattice interface barriers. In addition, a warm white light-emitting diode (LED) is successfully fabricated, exhibiting Commission Internationale de l'Eclairage (CIE) coordinates of (0.343, 0.335), a color rendering index (CRI) of 92.1, and a correlated color temperature (CCT) of 5013 K, showing significant application prospects for high-quality lighting devices.

27% slope efficiency in a WGM microcavity enabled by an Yb:YAG crystalline film

The choice of a laser gain medium is crucial in achieving efficient and high-power outputs of optically stimulated WGM microcavity lasers. This work employs an Yb:YAG crystalline film as the gain medium for the microdisk laser. The Yb:YAG crystalline film is exfoliated from a bulk of a Yb:YAG crystal by the ion-implantation-enhanced etching method. The crystalline film is shaped into a microdisk through focused ion beam milling. This Yb:YAG microdisk laser achieves a single-mode laser output (with a side-mode-suppression ratio of 27.8 dB) under a 946 nm laser pumping. The maximum slope efficiency reaches 27% with a maximum output power of 1.1 mW.

Ce/Mn/Cr: (Re,Y)3Al5O12 Phosphor Ceramics (Re = Gd, Tb and Lu) for White LED Lighting Significant Spectral Redshift and Improved Color-Rendering Index

In order to attain phosphor ceramics with a high Color-Rendering Index (CRI), samples with the composition of Y0.997-xRexCe0.003)3(Al0.9748 Mn2+0.024Cr3+0.0012)5O12(Rex = 0, Gd0.333, Gd0.666, Gd0.997, Tb0.333, Tb0.666, Tb0.997 and Lu0.997 were prepared by solid-state reaction and vacuum sintering, and exhibited potential for high-quality, solid-state lighting. Doping with Cr3+ and Mn2+ effectively enhanced the red component of Ce3+ spectra through the intense energy transfer from Ce3+ ions to Mn2+/Cr3+ ions. The crystal field splitting of [GdO8] and [TbO8] was more extensive than that of [YO8], causing a massive redshift in the Ce3+ emission peaks from 542 to 561 and 595 nm, while [LuO8] had an opposite effect and caused a blueshift with a peak position at 512 nm. White LED devices incorporating Ce/Mn/Cr: (Gd0.333Y0.664)3Al5O12 phosphor ceramic exhibited a high CRI of 83.97, highlighting the potential for enhancing the red-light component of white LED lighting.

Color Tunable Composite Phosphor Ceramics Based on SrAlSiN3:Eu2+/Lu3Al5O12:Ce3+ for High-Power and High-Color-Rendering-Index White LEDs/LDs Lighting

Lu3Al5O12:Ce3+ phosphor ceramics were fabricated by vacuum sintering. On this basis, a bi-layer composite phosphor was prepared by low-temperature sintering to cover the phosphor ceramics with a layer of SrAlSiN3:Eu2+-phosphor-in-glass (PiG). The optical, thermal, and colorimetric properties of LuAG:Ce3+ phosphor ceramics, SrAlSiN3:Eu2+ phosphors and SrAlSiN3:Eu2+-PiG were studied individually. Combining the bi-layer composite phosphors with the blue LED chip, it is found that the spectrum can be adjusted by varying the doping concentration of SrAlSiN3:Eu2+-PiG and the thickness of Lu3Al5O12:Ce3+ phosphor ceramics. The maximal color rendering index value of the white LED is 86, and the R9 is 61. Under the excitation of a laser diode, the maximum phosphor conversion efficacy of the bi-layer composite phosphors is 120 lm/W, the Ra is 83, and the correlated color temperature is 4534 K. These results show that the bi-layer composite phosphor ceramic is a candidate material to achieve high color rendering index for high brightness lighting.

Exclusive confinement of Bi3+-activators in the triangular prism enabling efficient and thermally stable green emission in the tridymite-type phosphor CaBaGa4O8:Bi3

Recently, Bi3+-activated phosphors have been extensively studied for potential applications in phosphor-converted white light-emitting diodes (pc-WLEDs). However, Bi3+ activators usually exhibit low quantum efficiency and poor thermal stability due to the outermost 6s6p-orbitals of Bi3+ being strongly coupled with the host lattice, inhibiting potential applications. Herein, we rationally design a novel phosphor CaBaGa4O8:Bi3+, which adopts a tridymite-type structure and crystallizes in the space group of Imm2. CaBaGa4O8:Bi3+ presents a bright green light emission peaking at 530 nm with a FWHM narrower than 90 nm. Comprehensive structural and spectroscopic analyses unravelled that Bi3+ emitters were site-selectively incorporated into the triangular prism (Ca2+-site) in CaBaGa4O8:Bi3+ since there exist two distinct crystallographic sites that can accommodate the Bi3+ ions. An excellent luminescence thermal stability of 73% of the ambient temperature photoluminescence intensity can be maintained at 423 K for CaBaGa4O8:0.007Bi3+. Impressively, the quantum efficiency (QE) of CaBaGa4O8:0.007Bi3+ was remarkably improved to 47.2% for CaBaGa4O8:0.007Bi3+,0.03Zn2+via incorporating the Zn2+ compensators without sacrificing the luminescence thermal stability. The high thermal stability and QE of CaBaGa4O8:0.007Bi3+,0.03Zn2+ are superior to most of the Bi3+-activated green-emitting oxide phosphors. The perspective applications in pc-WLEDs for CaBaGa4O8:0.007Bi3+,0.03Zn2+ were also studied by fabricating LED devices.

Barcode-structured YAG:Ce/YAG:Ce,Mn ceramic phosphors for variable CCT and high CRI LED/LD lighting

Ceramic phosphors are widely considered the next-generation phosphor material for white LED/LD lighting, and a wide spectrum is a key factor in improving the CRI of lighting sources. In this paper, a novel, to our knowledge, barcode-structured YAG:Ce/YAG:Ce,Mn ceramic phosphor was designed and fabricated. The lighting sources with the CRI value of 73.5 and 68.9 were obtained under the excitation of blue LEDs and blue LDs, respectively. Simultaneously, thanks to the effective supplementary emission from a red LD, the CRI of the ceramic-based lighting source reached 81.8 under blue LD excitation. Specifically, the microstructure and luminescent property of ceramic phosphors with different thicknesses and ion doping concentrations were systematically studied. Besides, by changing the blue power from 0.52 W to 2.60 W, the CCT of the laser lighting source with the encapsulation of optimized YAG:Ce/YAG:Ce,Mn ceramic phosphors ranged from 3928 K to 5895 K, while the CRI always maintained above 80. The above results indicate that barcode-structured Ce:YAG/Ce,MnYAG ceramic phosphor is a candidate to achieve a high CRI and ican be applied to various lighting occasions.

Synthesis, structure, and luminescence properties of Europium/Cerium/Terbium doped strontium-anorthite-type green phosphor for solid state lighting

Novel phosphor exploration and luminescence property regulation are two important strategies in pursing high performance phosphors for white light emitting diodes, and have attracted great attention from the researchers. Herein, novel green phosphors Sr₂Ga₂SiO₇:Eu²⁺ and Sr₂Ga₂SiO₇:Ce³⁺,Tb³⁺ had been obtained by high-temperature solid-state reactions and their luminescence properties had been investigated in detail. Powder X-ray diffraction and Rietveld structure refinement results verified the phase purity and gave the crystal structure of the prepared samples. Due to the electric dipole transition between inter configurations of 4f^N and 4f^N-15d¹, Sr₂Ga₂SiO₇:Eu²⁺ and Sr₂Ga₂SiO₇:Ce³⁺ exhibited intense broad excitation and emission bands, giving out green and blue emitting light under UV excitation, respectively. By codoping Tb³⁺ with Ce³⁺ in the host and utilizing the energy transfer, tunable blue to green emission had been obtained. The energy transfer mechanism had been determined to be electric dipole-quadrupole interaction through dynamic luminescence analysis using I-H model. The prepared phosphors exhibited good thermal stability with integral emission intensity at 150 °C remaining more than 80 % of the emission intensity at 25 °C. Moreover, by coating Sr₂Ga₂SiO₇:Eu²⁺ and Sr₂Ga₂SiO₇:Ce³⁺,Tb³⁺ on UV chips, green LED devices had been obtained. The investigation results indicated that the Eu²⁺ singly doped and Ce³⁺-Tb³⁺ codoped Sr₂Ga₂SiO₇ might be potential UV excited green phosphors for solid state lighting.

Multimodal Luminescent Low-Dimension Cs2ZrCl6:xSb3+ Crystals for White Light-Emitting Diodes and Information Encryption

Low-dimension perovskite materials have attracted wide attention due to their excellent optical properties and stability. Herein, Sb³⁺-doped Cs₂ZrCl₆ crystals are synthesized by a coprecipitation method in which Sb³⁺ ions partially replace Zr⁴⁺ ions. The Cs₂ZrCl₆:xSb³⁺ powder shows blue and orange-red emissions under a 254 and 365 nm light, respectively, due to the [ZrCl₆]^2- octahedron and [SbCl₆]^3- octahedron. The photoluminescence quantum yield (PLQY) of Cs₂ZrCl₆:xSb³⁺ (x = 0.1) crystals is up to 52.5%. According to experimental and computational results, the emission mechanism of the Cs₂ZrCl₆:xSb³⁺ crystals is proposed. On the one hand, a wide blue emission with a large Stokes shift is caused by the self-trapping excitons of [ZrCl₆]^2- octahedra under a 260 nm excitation. On the other hand, the luminescence mechanism of [SbCl₆]^3- octahedron is divided into two parts: ¹P₁ → ¹S₀ (490 nm) and ³P₁ → ¹S₀ (625 nm). The broad-band emission, high PLQY, and excellent stability endow the Cs₂ZrCl₆:xSb³⁺ powders with the potential for the fabrication of white light-emitting diodes (WLEDs). A WLED device is fabricated using a commercial 310 nm NUV chip, which shows a high color rendering index of 89.7 and a correlated color temperature of 5333 K. In addition, the synthesized Cs₂ZrCl₆:xSb³⁺ crystals can be also successfully used for information encryption. Our work will provide a deep understanding of the photophysical properties of Sb³⁺-doped perovskites and facilitate the development of Cs₂ZrCl₆:xSb³⁺ crystals in encrypting multilevel optical codes and WLEDs.

Multi-mode anti-counterfeiting guarantees from a single material CaCd2Ga2Ge3O12:Tb3+,Yb3+ - two stimuli-responsive and four-state emission

Luminescent anti-counterfeiting materials have drawn much attention in anti-counterfeiting applications due to their photochemical stability and emission patterns. However, conventional materials majorly use single-mode luminescence, leaving a growing demand for new materials to prevent counterfeiting. In this work, multi-mode anti-counterfeiting is guaranteed from a single luminescent material CaCd₂Ga₂Ge₃O₁₂:Tb³⁺,Yb³⁺via a high-temperature solid-state reaction. The experimental result showed that this single material features green luminescence with excellent photoluminescence, afterglow, thermoluminescence, and up-conversion luminescence, which are ascribed to Tb³⁺ transitions. Upon co-doping with Yb³⁺ as a sensitiser, the photo-stimuli responsiveness was achieved at 254 and 980 nm excitation sources, respectively, and the thermo-stimuli responsiveness was realised after exposure to UV of 254 nm for 10 s and heating at 45 °C, respectively. The band structure calculation, trap distribution, and effective trap depths were used to explain the luminescence mechanism. Based on the two-stimuli responsiveness and four-state emission performance, we prepared images of optical devices using silk screen printing technology. It was found that the images displayed green emission under different luminescence modes. The results prove that we successfully constructed an advanced luminescence anti-counterfeiting material.

(Sr, Ca)AlSiN3:Eu2+ Phosphor-Doped YAG:Ce3+ Transparent Ceramics as Novel Green-Light-Emitting Materials for White LEDs

In this work, based on Y₃Al₅O₁₂:Ce³⁺ (YAG:Ce³⁺) transparent ceramic and (Sr, Ca)AlSiN₃:Eu²⁺ phosphors, novel green-light-emitting materials were systematically studied. YAG:Ce³⁺ transparent ceramics with different doping-concentrations, from 0% to 1% (Sr, Ca)AlSiN₃:Eu²⁺ phosphors, were fabricated by dry pressing and vacuum sintering. The serial phosphor ceramics had 533 nm green-light emission when excited by 460 nm blue light. The PL, PLE, and chromaticity performances were measured, indicating that more of the green-light component was emitted with the increase in doping concentration. The addition of (Sr, Ca)AlSiN₃:Eu²⁺ phosphor increased the green-light wavelength area and improved the quantum yield (QY) of the YAG:Ce³⁺ ceramic matrix. The phase composition, microstructure, crystal-field structure and phosphor distribution of (Sr, Ca)AlSiN₃:Eu²⁺ phosphor-doped YAG:Ce³⁺ transparent ceramics were investigated, to explore the microscopic causes of the spectral changes. Impressively, (Sr, Ca)AlSiN₃:Eu²⁺ phosphors were distributed homogeneously, and the pinning effect of phosphor caused the suppression of grain growth. The novel materials could provide an effective strategy for full-spectrum white lighting and displaying applications in the future.

Preparation of high-quality YAG:Ce3+ ceramic phosphor by high-frequency induction heated press sintering methods

This study investigates the characteristics of a ceramic phosphor (CP) for the converter of a high-power laser diode-based automobile headlamp synthesized by high-frequency induction heated press (HFP) sintering. The CP prepared by an HFP method exhibits remarkable optical properties that are comparable to spark plasma sintering. The effects of post-treatment process for controlling residual pores, as well as sintering temperature, sintering pressure and heating rate for optimization of the HFP sintering method, were studied. The HFP sintering process can be widely used in ceramics and lighting fields because it is designed relatively low cost compared to other techniques and exhibits excellent productivity.

Enhanced Photoluminescence of Gd3Al4GaO12: Cr3+ by Energy Transfers from Co-Doped Dy3

LEDs for plant lighting have attracted wide attention and phosphors with good stability and deep-red emission are urgently needed. Novel Cr3+ and Dy3+ co-doped Gd3Al4GaO12 garnet (GAGG) phosphors were successfully prepared through a conventional solid-state reaction. Using blue LEDs, a broadband deep-red emission at 650−850 nm was obtained due to the Cr3+ 4T2 → 4A2 transition. When the Cr3+ concentration was fixed to 0.1 mol, the crystal structure did not change with an increase in the Dy3+ doping concentration. The luminous intensity of the optimized GAGG:0.1Cr3+, 0.01Dy3+ was 1.4 times that of the single-doped GAGG:0.1Cr3+. Due to the energy transfer from Dy3+ to Cr3+, the internal quantum efficiency reached 86.7%. The energy transfer from Dy3+ to Cr3+ can be demonstrated through luminescence spectra and fluorescence decay. The excellent properties of the synthesized phosphor indicate promising applications in the agricultural industry.

Fabrication of LuAG:Ce3+ Ceramic Phosphors Prepared with Nanophosphors Synthesized by a Sol-Gel-Combustion Method

The aim of this study was to investigate properties of ceramic phosphors fabricated using nano Lu₃Al₅O₁₂:Ce³⁺ phosphors produced with a sol-gel-combustion method. These nano Lu₃Al₅O₁₂:Ce³⁺ phosphors had a size of about 200 nm, leading to high density when fabricated as a ceramic phosphor. We manufactured ceramic phosphors through vacuum sintering. Alumina powder was added to improve properties. We mounted the manufactured ceramic phosphor in a high-power laser beam projector and drove it to determine its optical performance. Ceramic phosphor manufactured according to our route will have a significant impact on the laser-driven lighting industry.

Al2O3-YAG:Ce/YAG composite ceramic phosphor in a transmissive configuration for high-brightness laser-driven lighting

High-power, high-brightness laser lighting promotes new requirements for light-conversion materials, such as high thermal conductivity, high saturation threshold and compact encapsulation. In this paper, we designed and fabricated a novel composite structure ceramic including a 1.0 × 1.0 mm² Al₂O₃-YAG:Ce ceramic and a φ=16.0 mm transparent YAG ceramic for the transmissive configuration in laser lighting. When pumped by blue laser from 0∼60 W mm², all the samples exhibited no luminous saturation phenomenon, and the 10.0 wt.%Al₂O₃-YAG:Ce/YAG composite ceramic with the thickness of 0.3 mm maintained white light with a luminous efficacy over 200 lm/W. Moreover, a maximal luminous flux over 1000 lm, a correlated color temperature (CCT) of 5471 K, and an operating temperature as low as 92.3 °C were obtained under the excitation power density as high as 60 W/mm². The configuration that Al₂O₃-YAG:Ce encapsulated by YAG reflects an excellent optical and thermal properties by using transparent and highly thermally conductive YAG materials. These results indicate that Al₂O₃-YAG:Ce/ YAG composite ceramic phosphor is a promising candidate in transmissive configuration for automotive lighting and laser searchlight.

RGB Tricolor and Multimodal Dynamic Optical Information Encryption and Decoding for Anti-Counterfeiting Applications

Conventional optical anti-counterfeiting strategies are based on the single-color emission, which are easily deciphered and thus greatly limited in the application of information security. Herein, a multimodal dynamic optical information coding with red, green, and blue (RGB) tricolors has been developed by photoluminescence (PL), persistent luminescence (PersL), thermally stimulated luminescence (TSL), and thermally stimulated persistent luminescence (TSPL). The BaSi₂O₂N₂:Eu²⁺ phosphors with a blue emission peak at 494 nm were used as the crucial blue optical information coding material and exhibited the distinctive response properties to light, heat, and force stimuli with intrinsic trap depths of 0.674 and 0.82 eV. More importantly, by combining the red Sr₂Si₅N₈:Eu²⁺,Dy³⁺ and green SrSi₂O₂N₂:Eu²⁺,Dy³⁺ nitride phosphors, a RGB tricolor and multimodal strategy has been successfully developed for anti-counterfeiting applications. The "RGB tricolor flower" with RGB emissions is given as a typical example to achieve the dynamic display of optical information encryption and decoding through the various PL, PersL, TSL, and TSPL modes. Finally, the traditional quick response (QR) code mechanism has been integrated into the design of multi-information encrypted RGB tricolor anti-counterfeiting devices with different identifiabilities of the encrypted information in natural light, PL, PersL, TSL, and TSPL modes. The laminated layers of RGB QR code patterns containing different specific information, such as "DLPU" and "116034", can be effectively recognized in the corresponding modes. The design strategy of RGB tricolor and multimodal optical information encryption and decoding devices in this work greatly improves the security level of advanced optical information technologies and extends the potential applications in dynamic anti-counterfeiting fields.

Judd-Ofelt Analysis of High Erbium Content Yttrium-Aluminum and Yttrium-Scandium-Aluminum Garnet Ceramics

The Er1.5Y1.5Al5O12 (Er:YAG) and (Er1.43Y1.43Sc0.14)(Sc0.24Al1.76)Al3O12 (Er:YSAG) ceramics have been characterized using the Judd-Ofelt (JO) theory. The line strengths and oscillator strengths of several transitions from the ground state 4I15/2 to excited state manifolds have been evaluated from transmittance spectra measured at room temperature (300 K). The JO parameters have been calculated, and the values of the radiative decays rate and the radiative lifetimes for the 4I13/2 excited state, and the luminescence cross-section of 4I15/2 → 4I13/2 in Er-doped ceramic samples have been established. We have traced the influence of Sc3+ inclusion on spectroscopic properties and crystal quality and estimate prospects of application in laser systems.

High-Efficiency Continuous-Luminescence-Controllable Performance and Antithermal Quenching in Bi3+-Activated Phosphors

Recently, Bi³⁺-activated phosphors have been widely researched for phosphor-converted light-emitting diode (pc-LED) applications. Herein, novel full-spectrum A₃BO₇:Bi³⁺ (A = Gd, La; B = Sb, Nb) phosphors with a luminescence-tunable performance were achieved by a chemical substitution strategy. In the La₃SbO₇ host material, a new luminescent center was introduced, with Gd³⁺ replacing La³⁺. The photoluminescence (PL) spectra show a large blue shift from 520 to 445 nm, thus achieving regulation from green to blue lights. Moreover, a series of solid solution-phase phosphors La₃Sb_1-xNb_xO₇:Bi³⁺ were prepared by replacing Sb with Nb, and a PL spectral tunability from green (520 nm) to orange-red (592 nm) was realized. Temperature-dependent PL spectra show that La_3-xGd_xSbO₇:Bi³⁺ phosphors have excellent thermal stability. Upon 350 nm excitation, the PL intensity of La_3-xGd_xSbO₇:Bi³⁺ phosphors at 150 °C remained at more than 93% at room temperature. With Gd³⁺ doping, the thermal stability gradually improved, and LaGd₂SbO₇:0.03Bi³⁺ represents splendid antithermal quenching (135.2% at 150 °C). Finally, a full-visible spectrum for pc-LED with a high color-rendering index (Ra = 94.4) was obtained. These results indicated that chemical substitution is an effective strategy to adjust the PL of Bi³⁺, which is of great significance in white-light illumination and accurate plant lighting.

Photoluminescence and Thermoluminescence in Dy3+ , Ce3+ and Tb3+ activated MgB4 O7 phosphor for dosimetry application

Samples of microcrystalline rare earth doped magnesium borate materials were synthesized via. modified solid state diffusion and were characterized by X-ray diffraction (XRD) and Scanning electron microscopy (SEM) techniques. Photoluminescence (PL) results of MgB₄ O₇ :Dy sample depicts blue emission resulted from (⁴ F_9/2 -⁶ H_15/2 ) transition peaked at 484 nm, which is much stronger than yellow emission arising due to the (⁴ F_9/2 -⁶ H_13/2 ) at 576 nm. From emission spectra of MgB₄ O₇ :Tb, it looks that, at higher concentration of Tb³⁺ ion, the green emission becomes strong and strong which directly relates the energy transfer from ⁵ D₃ excited state to ⁵ D₄ excited state by a cross-relaxation while blue emission gets suppressed in MgB₄ O₇ phosphors. The TL of the samples was taken immediately after the irradiation and compared the TL curve with CaSO₄ :Dy. MgB₄ O₇ :Dy showed very good TL sensitivity for the desirable dosimetric curve at about 218°C and the best glow curve structure. In comparison to dosimetric peak of MgB₄ O₇ :Ce and MgB₄ O₇ :Tb, MgB₄ O₇ :Dy phosphor is equally sensitive to CaSO₄ : Dy. MgB₄ O₇ :Dy and MgB₄ O₇ :Tb have shown linearity for 1-5 kGy dose. The activation energies and frequency factors are also calculated for samples MgB₄ O₇ :RE (RE=Dy, Tb, Ce) using peak shape method.

Highly efficient Ce: Lu(Mg,Al)2(Si,Al)3O12 phosphor ceramics for high-power white LEDs/LDs

Lu₃Al₅O₁₂: Ce³⁺ (LuAG: Ce³⁺) phosphor ceramics (PCs) with high quantum efficiency and excellent thermal stability are incredibly promising color converters for high-power white light emitting diodes (LEDs)/ laser diodes (LDs) lighting. However, the greenish emission of LuAG:Ce³⁺ PCs does not allow to reach white light emission upon pumping by a blue LED/ LD without an additional red luminescent material. In this work, a series of (Ce_0.003Lu_0.997)₃(MgxAl_1-2xSix)₅O₁₂ (LCMASG) (x = 0-0.15) PCs were fabricated by solid state reaction method. Impressively, the as-prepared PCs exhibited a distinct red-shift (513→538nm) and a 17% increase of the color index (CRI) of high-power white LED(58.4→70.4). Particularly, Ce: Lu(Mg, Al)₂(Si, Al)₃O₁₂ PC with 15 at.% substitution concentration showed only 8% luminescent intensity loss at 150 °C and high internal quantum efficiency (IQE) of 82%, exhibiting desirable optical thermal stability. By combining with a 460 nm blue chip or a 455 nm laser source, white LED/LD devices based on the LCMASG PCs in a remote excitation mode were constructed. The optimized luminous efficiency of Ce: Lu(Mg, Al)₂(Si, Al)₃O₁₂ PC with 15 at.% Mg²⁺/Si⁴⁺ doping up to 176.4 lm/W was obtained as the power density of the blue laser increased to 6.52 W/mm². Also, a 4053K CCT of the warm white light emission was realized. Therefore, this work proves that the LCMASG PCs are promising to serve as color converters for high power LEDs/LDs lighting in the future.

Utilizing the energy transfer mechanism to realize color tunable luminescence

Bi³⁺/Eu³⁺ co-doped phosphors can realize multi-color luminescence by adjusting the concentration ratio, which makes it possible to manually control the emission color. On this basis, a series of Bi³⁺/Eu³⁺ co-doped phosphors SrLaGa₃O₇:xBi³⁺,yEu³⁺ were prepared. The existence of energy transfer from Bi³⁺ to Eu³⁺ was verified by spectral analysis. The emission spectra of SrLaGa₃O₇:xBi³⁺ show a wide-band peaking at 472 nm. For SrLaGa₃O₇:xBi³⁺,yEu³⁺, the Bi³⁺ → Eu³⁺ energy transfer occurs and a series of sharp emitting peaks of Eu³⁺ can be observed simultaneously. The relative luminescence intensity of Bi³⁺ and Eu³⁺ can be modulated by changing the relative concentrations of Bi³⁺ and Eu³⁺. Using this mechanism, the color tunable luminescence of SrLaGa₃O₇:xBi³⁺,yEu³⁺ from cyan, through white to orange, and finally to red is realized. By using a 320 nm UV chip and SLG:0.06Bi³⁺,0.07Eu³⁺ white phosphor, a white light-emitting diode (WLED) lamp was fabricated with chromaticity coordinates of (0.3199, 0.3083) and a color rendering index R_a of 82. This indicates that the prepared sample is a very promising candidate in the LED field.

Highly Efficient Broad-Band Green-Emitting Cerium(III)-Activated Garnet Phosphor Allows the Fabrication of Blue-Chip-Based Warm-White LED Device with a Superior Color Rendering Index

High-performance warm-white light-emitting diode (LED) devices are in great demand toward green and comfortable solid-state lighting. Herein, we report a creative green-emission CaY₂HfGa(AlO₄)₃:Ce³⁺ phosphor. CaY₂HfGa(AlO₄)₃:Ce³⁺ compounds with different cerium ion doping contents have been successfully prepared through a conventional high-temperature solid-state method, and their phase and crystal structure have been revealed via the powder X-ray diffraction and Rietveld refinement. Impressively, the CaY₂HfGa(AlO₄)₃:Ce³⁺ phosphors exhibit a broad-band excitation, which well covers the wavelength region from the 300 to 500 nm, corresponding to the commercial blue-emitting LED chip. Upon 450 nm excitation, the optimal CaY₂HfGa(AlO₄)₃:2%Ce³⁺ sample shows an intense broad-band green emission (the corresponding testing spectral range: 460-750 nm) with a strongest peak about 534 nm. In addition, the CaY₂HfGa(AlO₄)₃:2%Ce³⁺ sample possesses a broad full width at half-maximum equal to 120 nm; moreover, its CIE chromaticity coordinate and the internal quantum efficiency are determined to be (0.3541, 0.5427) and 72.8%, respectively. A high-quality warm-white LED has been fabricated through incorporating our CaY₂HfGa(AlO₄)₃:2%Ce³⁺ green phosphors and commercial red phosphors with the 450 nm blue LED chip. When upon the 20 mA bias driving current, the LED device demonstrates a bright warm-white light emission, which possesses a satisfactory color rendering index of 91, a low correlated color temperature of 4080 K, as well as a good luminous efficacy of 85.14 lm W^-1. The creative green-emitting CaY₂HfGa(AlO₄)₃:Ce³⁺ garnet phosphor has a bright application prospect toward high-quality warm-white LED lighting.

Ultrasonic Spray Pyrolysis Synthesis and Photoluminescence of LuAG:Ce Thin Films

LuAG:Ce (Lu₃Al₅O₁₂:Ce) is one of the most important color converters in white lighting industry. Especially, LuAG:Ce film attracts more attention due to the outstanding advantages, such as the efficient heat dissipation, the saving of rare earth, and so on. Here, LuAG:Ce film on sapphire was successfully prepared by the ultrasonic spray pyrolysis process. The phase, microstructure and photoluminescence of LuAG:Ce films were investigated. LuAG:Ce films had a thickness of around 5 μm, which were well crystallized at 1000 °C in air atmosphere to form the typical garnet structure. Under the protection of CO atmosphere, increasing the annealing temperature greatly enhanced the photoluminescence performance. After annealing at 1500 °C for 5 h in CO atmosphere, 3.0 mol.% Ce³⁺ doped LuAG:Ce film exhibited the highest emission and excitation intensity. The emission intensity of 3.0 mol.% Ce³⁺ doped LuAG:Ce film annealed at 1500 °C in CO atmosphere increased up to five times, when compared with the best LuAG:Ce film annealed at 1000 °C in air atmosphere. The effects of Ce³⁺ doping concentration on the photoluminescence were also examined. As the Ce³⁺ doping concentration increased from 0.2 mol.% to 7.0 mol.%, the color of LuAG:Ce films changed from yellowish green to greenish yellow. When coupling the 3.0 mol.% Ce³⁺ doped LuAG:Ce film with a 0.5 W 450 nm blue laser, the formed device successfully emitted white light.

Upconversion Properties and Temperature-Sensing Behaviors of Alkaline-Earth-Metal Scandate Nanocrystals Doped with Er3+/Yb3+ Ions in the Presence of Alkali Ions (Li+, Na+, and K+)

Temperature-sensing media based on the fluorescence intensity ratio (FIR) of upconversion materials that suffer from low sensitivity owing to the small energy gap still have a need for new compounds with strong upconversion luminescence (UCL). In this work, a series of MSc₂O₄:Er³⁺/Yb³⁺ (M = Mg, Ca, Sr, and Ba) nanocrystals were prepared by a hydrothermal method using NaOH alkaline solution. The structure, morphology, and UCL characteristics of materials were investigated, and the red UCL of the CaSc₂O₄:Er³⁺/Yb³⁺ sample was dramatically enhanced by a factor of ∼12, ∼23, and ∼2000 compared with SrSc₂O₄, MgSc₂O₄, and BaSc₂O₄ samples, respectively. By adjusting alkali ions (Li⁺, Na⁺, K⁺), the UCL intensities of CaSc₂O₄:Er³⁺/Yb³⁺ and SrSc₂O₄:Er³⁺/Yb³⁺ samples were further improved, especially in the presence of Li⁺ ions. Excellent temperature-sensing behaviors are realized for CaSc₂O₄:Er³⁺/Yb³⁺ and SrSc₂O₄:Er³⁺/Yb³⁺ samples in the presence of Li⁺ ions, in which the maximum absolute sensitivity S_A values are about 0.0041 and 0.0036 K^-1 at 600 K and the corresponding relative sensitivity S_R values are expressed as 1197/T² and 1129/T² (the current optimal S_R = 1289/T²), respectively. The intense UCL and excellent S_A and S_R values indicate that CaSc₂O₄:Er³⁺/Yb³⁺ and SrSc₂O₄:Er³⁺/Yb³⁺ materials are promising candidates for application in high-temperature sensors working under 980 nm excitation.

Glass-Crystallized Luminescence Translucent Ceramics toward High-Performance Broadband NIR LEDs

Near-infrared (NIR) phosphor-converted light-emitting diodes (pc-LEDs) are newly emergent broadband light sources for miniaturizing optical systems like spectrometers. However, traditional converters with NIR phosphors encapsulated by organic resins suffer from low external quantum efficiency (EQE), strong thermal quenching as well as low thermal conductivity, thus limiting the device efficiency and output power. Through pressureless crystallization from the designed aluminosilicate glasses, here broadband Near-infrared (NIR) emitting translucent ceramics are developed with high EQE (59.5%) and excellent thermal stability (<10% intensity loss and negligible variation of emission profile at 150 °C) to serve as all-inorganic visible-to-NIR converters. A high-performance NIR phosphor-converted light emitting diodes is further demonstrated with a record NIR photoelectric efficiency (output power) of 21.2% (62.6 mW) at 100 mA and a luminescence saturation threshold up to 184 W cm-2 . The results can substantially expand the applications of pc-LEDs, and may open up new opportunity to design efficient broadband emitting materials.

Structural and Luminescence Behavior of Nanocrystalline Orthophosphate KMeY(PO4)2: Eu3+ (Me = Ca, Sr) Synthesized by Hydrothermal Method

KMeY(PO₄)₂:5% Eu³⁺ phosphates have been synthesized by a novel hydrothermal method. Spectroscopic, structural, and morphological properties of the obtained samples were investigated by X-ray, TEM, Raman, infrared, absorption, and luminescence studies. The microscopic analysis of the obtained samples showed that the mean diameter of synthesized crystals was about 15 nm. The KCaY(PO₄)₂ and KSrY(PO₄)₂ compounds were isostructural and they crystallized in a rhabdophane-type hexagonal structure with the unit-cell parameters a = b ≈ 6.90 Å, c ≈ 6.34 Å, and a = b ≈ 7.00 Å, c ≈ 6.42 Å for the Ca and Sr compound, respectively. Spectroscopic investigations showed intense ⁵D₀ → ⁷F₄ transitions connected with D₂ site symmetry of Eu³⁺ ions. Furthermore, for the sample annealed at 500 °C, europium ions were located in two optical sites, on the surface of grains and in the bulk. Thermal treatment of powders at high temperature provided better grain crystallinity and only one position of dopant in the crystalline structure. The most intense emission was possessed by the KSrY(PO₄)₂:5% Eu³⁺ sample calcinated at 500 °C.

Photoluminescence Properties of AScSi2O6:Cr3+ (A = Na and Li) Phosphors with High Efficiency and Thermal Stability for Near-Infrared Phosphor-Converted Light-Emitting Diode Light Sources

Near-infrared (NIR) phosphors are fascinating photoluminescence materials with applications in phosphor-converted light-emitting diodes (pc-LEDs) for night vision lighting, which are still restricted by low efficiency and thermal stability in the current research stage. In this work, AScSi₂O₆ (A = Na/Li) are chosen as hosts due to a larger band gap and a single octahedral site for Cr³⁺ doping. The NIR-emitting Cr³⁺-activated AScSi₂O₆:Cr³⁺ phosphors were successfully prepared by a common high-temperature solid-state method. X-ray diffraction and Rietveld refinement confirm that the Cr³⁺ prefers to enter the Sc³⁺-octahedral lattice site in the AScSi₂O₆ structure. Under blue light excitation, AScSi₂O₆:Cr³⁺ phosphors exhibit broadband NIR emission from 700 to 1100 nm with a full width at half-maximum of ∼150 nm owing to the ⁴T₂ → ⁴A₂ electron transition of Cr³⁺. The photoluminescence properties were enhanced by adjusting the fluxes and sintering conditions, and highly efficient LiScSi₂O₆:Cr³⁺ NIR phosphors with external quantum efficiencies of 33.4% were obtained. Moreover, the optimized LiScSi₂O₆:Cr³⁺ exhibits excellent thermal stability (75% at 150 °C) with an activation energy of 0.33 eV. Importantly, the fabricated NIR pc-LED with the highly efficient LiScSi₂O₆:Cr³⁺ phosphor demonstrates brighter NIR light and a higher luminous efficacy than the NaScSi₂O₆:Cr³⁺ phosphor in night vision.

Elaborate Size-Tuning of Silica Aerogel Building Blocks Enables Laser-Driven Lighting

Silica aerogels with accurate building-block control are realized by adjusting the surfactant concentration during the synthesis process. The resulting silica-aerogel monolith with spherical building blocks of ≈24-40 nm, together with a deliberately created hole along the incident light direction, shows an incredibly promising application in monochromatic laser-driven lighting. The resulting coefficient of illuminance variation is as low as 8.1%, significantly outperforming commercially available ground-glass diffusers (139.0%) and polymer diffusers (249.1%); the speckle contrast is lower, as well as better, than that can be recognized by the human eye (4%), and the illuminance uniformity in the range of 0.770-0.862 is much better (higher) than that indoor workplace lighting required by the International Organization for Standardization. Lighting with any color in the visible spectrum, including white, can be obtained by using three primary color lasers (450, 532, and 638 nm) with different powers simultaneously as the light source. The resulting silica aerogel, which has excellent thermal stability, high laser-damage threshold, outstanding mechanical performance, and superhydrophobicity, can be further applied to long-distance and noncontact laser-driven lighting in rain or underwater without any additional encapsulation components.

An organic-inorganic hybrid K2TiF6 : Mn4+ red-emitting phosphor with remarkable improvement of emission and luminescent thermal stability

A new type of monoethanolamine (MEA) and Mn4+ co-doped KTF : MEAH+, Mn4+ (K2TiF6 : 0.1MEAH+, 0.06Mn4+) red emitting phosphor was synthesized by an ion exchange method. The prepared Mn4+ co-doped organic-inorganic hybrid red phosphor exhibits sharp red emission at 632 nm and the emission intensity at room temperature is 1.43 times that of a non-hybrid control sample KTF : Mn4+ (K2TiF6 : 0.06Mn4+). It exhibits good luminescent thermal stability at high temperatures, and the maximum integrated PL intensity at 150 °C is 2.34 times that of the initial value at 30 °C. By coating a mixture of KTF : MEAH+, Mn4+, a yellow phosphor (YAG : Ce3+) and epoxy resin on a blue InGaN chip, a prototype WLED (white light-emitting diode) with CCT = 3740 K and R a = 90.7 is assembled. The good performance of the WLED shows that KTF : MEAH+, Mn4+ can provide a new choice for the synthesis of new Mn4+ doped fluoride phosphors.