Full-Spectrum White Light-Emitting Diodes Enabled by an Efficient Broadband Green-Emitting CaY2ZrScAl3O12:Ce3+ Garnet Phosphor

Research progress on the design and regulation of Eu2+/Ce3+-activated anti-/zero thermal quenching phosphors

Luminescent materials have played a vital role in human society, with phosphor-converted light-emitting diodes (pc-LEDs) representing the cutting-edge in lighting solutions. As societal demands for improved material quality continue to rise, the quest for materials with enhanced performance has become paramount. Eu2+/Ce3+-activated inorganic luminescent materials have garnered significant attention due to their high luminescence efficiency and tunable properties. Recent research has focused on developing Eu2+/Ce3+-activated inorganic luminescent materials with anti-/zero thermal quenching behavior, leveraging the benefits of host structures and activator ions. To facilitate their commercial viability, a comprehensive understanding of their properties, mechanisms, and current status is essential. This study delves into the luminescence mechanisms of Eu2+/Ce3+ activator ions, provides a detailed analysis of the typical thermal behaviors of Eu2+/Ce3+-activated inorganic phosphors, outlines strategies for enhancing thermal stability from both intrinsic and extrinsic perspectives, and categorizes the reported instances of anti-/zero thermal quenching in Eu2+/Ce3+-activated phosphors. Lastly, drawing on the present landscape, this paper offers insights into the future development and prospects of similar phosphors, aiming to serve as a valuable reference for the advancement of Eu2+/Ce3+-activated inorganic luminescent materials.

Mn4+-activated Sc-based hexafluoride red phosphor K5Sc3F14: Synthesis, luminescence, and its applications in blue-pump WLEDs

Due to the advantages of low phonon energy, structural diversity, excellent thermal stability and optical properties, fluoride compounds have sparked considerable research attention. On this foundation, a novel red-emitting phosphor, K5Sc3F14:Mn4+ (abbreviated as KSF:Mn4+), was successfully designed and synthesized via a conventional co-precipitation process. The phosphor was comprehensively analyzed in terms of its phase, structure, morphology, elemental composition, and optical performance. Under blue light (473 nm) excitation, seven discernible emission peaks appear at 599, 609, 613, 622, 630, 634, and 647 nm, which can be attributed to the 2Eg to 4A2g transition of the Mn4+ ions. Furthermore, the optimal molar ratio of K5Sc3F14:K2MnF6 and crystal-field parameters (CFPs) are amply discussed. Ultimately, a warm WLED lamp with a high CRI (Ra = 87.5) and a low CCT (3289 K) was successfully created through the combination of a synthesized KSF:Mn4+ phosphor and a well-known YAG:Ce3+ phosphor, demonstrating that the developed phosphor is an appealing red component for high-performance warm white illumination.

CaLu2Sc2Al2SiO12:Ce3+ Green Phosphors for High-Quality White LEDs

Phosphors with broadband green emission are highly desirable for the construction of high-color-rendering warm-white light-emitting diode (LED) devices toward healthy solid-state lighting applications. However, most of the reported green phosphors are subject to an undesirable emission bandwidth and low quantum efficiency. Here, a highly efficient broadband green-emitting garnet phosphor, CaLu2Sc2Al2SiO12:Ce3+ (CLSASO:Ce3+), is successfully synthesized and investigated in detail. Upon excitation of 440 nm blue light, the as-synthesized CLSASO:3%Ce3+ phosphor features a wide bandwidth with a maximum peak situated at 534 nm and a large full width at half-maximum (fwhm) of 114 nm, which is superior to the commercial green phosphor of LuAG:Ce3+ (fwhm = 108 nm). As expected, the optimal CLSASO:3%Ce3+ sample also demonstrates satisfactory internal/external quantum efficiency of 78.3/50.1%, along with suitable CIE color coordinates of (0.3462, 0.5496). Meanwhile, temperature-dependent emission spectra measurements indicate that it retains 46% of the original integral intensity at 423 K against room temperature, together with an excellent color stability of 9.2 × 10-3. Finally, a fabricated blue-light-pumped prototype LED device with the proposed CLSASO:3%Ce3+ green component and another commercial CaAlSiN3:Eu2+ red phosphor delivers a brilliant warm-white light with a desirable color rendering index (Ra = 90.2), an acceptable color temperature of 4047 K and a superior luminous efficiency of 65.6 lm W-1. The findings illustrate that the construction of blue-light-excitable broadband green luminescence conversion material is beneficial for the preparation of a high-color-rendering warm-white LED device for high-quality general lighting applications.

Theoretically Guided Development of Excitation-Wavelength-Dependent Multifunctional Phosphor Based on Gallium Vacancy Perturbation

Constructing multifunctional phosphors grounded in the intricate relationship between energy level structures and luminescent properties has captivated researchers in the luminescent material field. Herein, using the embedded cluster multiconfigurational ab initio method, the energy levels of Bi3+ in the SrLaGa3O7 host at different geometries were calculated, which results in the establishment of complete configurational coordinate curves, yielding breathing mode vibrational frequencies and equilibrium bond lengths for all excited states. These curves supply deep insight into the luminescence properties of Bi3+-doped phosphors and highlight the impact of ions in the second coordination sphere on luminescence. Inspired by the calculated results, we designed SrLaGa3(1-x)O7-δ:0.01 Bi3+ phosphors with different Ga3+ reductions. The artificially introduced gallium vacancy results in perturbed Bi3+ luminescence, as verified by systematic experimental analysis, and causes the material to exhibit a novel greenish-yellow emission band in addition to the original blue band, leading to excitation-wavelength-dependent multicolor emission phosphors. The obtained phosphor displayed a multicolor fluorescent anticounterfeiting function, and a multicolor switching system was designed with the merits of direct visualization and easy identification of encrypted information. Additionally, white light-emitting diodes were fabricated by employing the prepared phosphors and UV chips. These results indicate that the SrLaGa3(1-x)O7-δ:0.01 Bi3+ phosphor has significant potential in both anticounterfeiting and lighting applications. Our study demonstrates the necessity of considering two coordinate spheres of ligands when interpreting the luminescent properties and illustrates the effectiveness of spectral design under theoretical guidance, providing a feasible path for the development of multifunctional phosphors.

Phosphor-converted light-emitting diodes in the marine environment: current status and future trends

The exploitation and utilization of resources in marine environments have ignited a demand for advanced illumination and optical communication technologies. Light-emitting diodes (LEDs), heralded as "green lighting sources", offer a compelling solution to the technical challenges of marine exploration due to their inherent advantages. Among the myriad of LED technologies, phosphor-converted light-emitting diodes (pc-LEDs) have emerged as frontrunners in marine applications. At the heart of pc-LEDs lie phosphor materials, colour-converters that orchestrate the emission of light. In the marine environment, blue-green light with a wavelength of 440-570 nm exhibits the deepest penetration depth, while other wavelengths are rapidly attenuated in the shallow layer. Additionally, specific wavelengths of light are crucial for particular applications. However, the moist marine environment as well as the demand for continuous and stable lighting pose a formidable challenge to the environmental stability of the phosphors. Therefore, developing blue-green phosphors with exceptional colour purity and high thermal and moisture stability is paramount for marine applications. Herein, this review delves into the application of LED and pc-LED technology in underwater optical communication and marine fishery, exploring the development strategies of phosphors tailored for the marine environment. The insights presented serve as a valuable reference for further research on phosphors and pc-LED devices.

Solution Processed Bilayer Metal Halide White Light Emitting Diodes

Metal halide perovskites and perovskite-related organic metal halide hybrids (OMHHs) have recently emerged as a new class of luminescent materials for light emitting diodes (LEDs), owing to their unique and remarkable properties, including near-unity photoluminescence quantum efficiencies, highly tunable emission colors, and low temperature solution processing. While substantial progress has been made in developing monochromatic LEDs with electroluminescence across blue, green, red, and near-infrared regions, achieving highly efficient and stable white electroluminescence from a single LED remains a challenging and under-explored area. Here, a facile approach to generating white electroluminescence is reported by combining narrow sky-blue emission from metal halide perovskites and broadband orange/red emission from zero-dimensional (0D) OMHHs. For the proof of concept, utilizing TPPcarz+ passivated two-dimensional (2D) CsPbBr3 nanoplatelets (NPLs) as sky blue emitter and 0D TPPcarzSbBr4 as orange/red emitter (TPPcarz+ = triphenyl (9-phenyl-9H-carbazol-3-yl) phosphonium), white LEDs (WLEDs) with a solution processed bilayer structure have been fabricated to exhibit a peak external quantum efficiency (EQE) of 4.8% and luminance of 1507 cd m-2 at the Commission Internationale de L'Eclairage (CIE) coordinate of (0.32, 0.35). This work opens a new pathway for creating highly efficient and stable WLEDs using metal halide perovskites and related materials.

A novel fluorescent material K3NbOF6: Mn4+ for light-emitting diode devices

A series of K3Nb1-xOF6:xMn4+ fluorescent materials were prepared by the cation exchange method. Phase structure, morphology, emission, excitation spectrum and LED packaging of fluorescent materials were tested. The fluorescent material particles are micron-sized (5 μm-20 μm) and have a micro-rod morphology. It has two absorption bands, with the blue light region (∼468 nm) being stronger than the ultraviolet region (∼370 nm). Under the excitation of 468 nm, it shows good narrowband emission in the red light region, mainly with anti-stokes v6 (∼627 nm), which is caused by the double barrier of the 2Eg→4A2g transition broken by the coupling effect of electron and phonon. The optimum doping concentration was 9.1 %, and as the concentration increased again, the dipole-dipole interaction between Mn4+ resulted in concentration quenching. When the fluorescent material operates at high temperature (150 ℃), the emission intensity drops to 50.2 % of which at room temperature. At high temperature, the electrons absorb a large amount of heat energy, and the non-radiation transition to 4A2g energy level causes the thermal quenching effect. In addition, the sample also showed good water stability, after 1 h of hydrolysis, the luminescence intensity decreased to 85.6 % of the initial value. The use of LED packaging with fluorescent materials and InGaN-YAG:Ce3+ can effectively reduce the color temperature of LED from 6856 K to 3745 K, and enhance the Color index from 61.5 % to 76.8 %. Which has great potential for development in the fields of plant growth and backlight display technology.

Design of Dual-Mode Optical Thermometry Based on Thermally Activated Efficient Energy Transfer in LaNbO4/Ln3+ (Eu3+/Sm3+/Pr3+) Phosphors

Exploring methods to achieve high thermal stability in phosphors is of great significance for their applications in high-temperature fields. Currently, energy transfer (ET) from the host to activator lanthanide ions (Ln3+) is an effective approach to improving the antithermal quenching of phosphors. In this contribution, LaNbO4 (LNO) with efficient blue emission is used as the host to construct the host-Ln3+ dual-emitting LNO/Ln3+ (Eu3+/Sm3+/Pr3+) phosphor system, and the ET efficiency under thermal activation is investigated. Experimental results indicate that as the temperature rises, the ET efficiency from the LNO host to activator Ln3+ increases, resulting in completely opposite luminescent thermal responses between the LNO host and activator Ln3+. That is, the emission of the LNO host undergoes thermal quenching, while the emission of activator Ln3+ exhibits antithermal quenching, where the integrated luminescence intensity at 498 K is 2.50-3.73 times that at 298 K. Therefore, based on the differing luminescent thermal response trends of the emission peaks of the phosphors, a dual-mode optical temperature sensing system can be designed using fluorescence intensity ratio and fluorescence color change, achieving high relative sensitivity. Thus, this work provides new insights into the design of host ET phosphors and their applications in optical temperature sensing.

Full-Visible-Spectrum White LEDs Enabled by a Blue-Light-Excitable Cyan Phosphor

Efficient blue-light-excitable broadband cyan-emitting phosphors may yield full-visible-spectrum white light-emitting diodes (WLEDs) with ultrahigh color rendering (Ra > 95). However, this requires closing the "cyan gap" in the 480-520 nm region of the visible spectrum, which is challenging. Herein, a well-performed cyan-emitting garnet phosphor Ca2LuAlGa2Si2O12:Ce3+ (CLAGSO:Ce3+) is reported. Under 430 nm excitation, the optimal CLAGSO:5%Ce3+ compound exhibits a broadband cyan emission (peak, 496 nm; bandwidth, 102 nm) with a high internal quantum efficiency of 85.6% and an excellent thermal resistance performance (69.1% at 423 K). Importantly, this as-prepared cyan-emitting phosphor provides sufficient cyan emission and enables filling the well-known so-called "cyan gap" between the blue LED chip and the commercial Y3Al5O12:Ce3+ (YAG:Ce3+) yellow phosphor. Impressively, a WLED device fabricated with the optimal CLAGSO:5%Ce3+ sample shows a low correlated color temperature (4053 K) and an ultrahigh color rendering index (Ra = 96.6), as well as an excellent luminous efficacy (74.09 lm W-1). These results highlight the importance of blue-excited broadband cyan-emitting phosphors in closing the cyan gap and enabling human-centric full-visible-spectrum warm WLED devices for high-quality solid-state lighting.

Structural and luminescence properties of novel Eu3+-doped Na3Ba2LaNb10O30 phosphors with high quantum efficiency and excellent color purity for w-LED applications

In this study, we report the successful synthesis and thorough characterization of Eu3+-doped Na3Ba2LaNb10O30 phosphors, targeting their application in white-light-emitting diodes (w-LEDs). The phosphors were synthesized using a high-temperature solid-state method, ensuring robust incorporation of Eu3+ ions into the host lattice. Comprehensive analyses were performed, including X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray (EDX) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy and Raman spectroscopy, confirming the phase purity, crystallinity, morphology, and elemental composition of the phosphors. We have also studied the electronic structure using diffuse reflectance spectroscopy (DRS). Photoluminescence studies revealed strong red emissions under near-ultraviolet light excitation, with the optimal Eu3+ doping concentration identified to be 9 mol%. Quantum-yield measurements demonstrated high luminescence efficiency, while chromaticity coordinates indicated excellent color purity suitable for w-LED applications. These findings contribute significantly to the advancement of phosphor materials for solid-state lighting, suggesting promising prospects for their integration into commercial LED devices.

Preparation and Luminescence Properties of Broadband Orange-Emitting Persistent ScBaZn3GaO7:Bi3+ Phosphor

This article describes a new kind of afterglow material, ScBaZn3GaO7:Bi3+, which was synthesized through a high-temperature solid-phase method. Its crystal structure, photoluminescent characteristics, and afterglow characteristics were studied and analyzed. Upon excitation at 344 nm, ScBaZn3GaO7:Bi3+ exhibits broadband emission with a central wavelength located at 571 nm (fwhm = 172.98 nm). The sample exhibits an internal quantum efficiency of 65.1%. The bright yellow persistent luminescence of the ScBaZn3GaO7:Bi3+ sample was observed after 365 nm irradiation. Thermoluminescence spectroscopy revealed four primary traps within ScBaZn3GaO7:Bi3+, with depths of 0.676, 0.794, 0.882, and 0.972 eV. The traps located at energy levels of 0.676 and 0.794 eV were identified as the key contributors to the sample's afterglow. Finally, the ScBaZn3GaO7:Bi3+ sample was combined with a UV-LED chip to fabricate a high-power warm white-light-emitting diode (WLED) device, indicating the potential application prospect of ScBaZn3GaO7:Bi3+ phosphor in single-phase warm WLEDs.

Dual-functional application of Ca2Ta2O7:Bi3+/Eu3+ phosphors in multicolor tunable optical thermometry and WLED

A series of Bi3+/Eu3+ co-doped Ca2Ta2O7 (CTO:Bi3+/Eu3+) phosphors were prepared by high-temperature solid-state method for dual-emission center optical thermometers and white light-emitting diode (WLED) device. By modulating the doping ratio of Bi3+/Eu3+ and utilizing the energy transfer from Bi3+ to Eu3+, the tunable color emission ranging from green to reddish-orange was realized. The designed CTO:0.04Bi3+/Eu3+ optical thermometers exhibit significant thermochromism, superior stability, and repeatability, with maximum sensitivities of Sa = 0.055 K-1 (at 510 K) and Sr = 1.298% K-1 (at 480 K) within the temperature range of 300-510 K, owing to the different thermal quenching behaviors between Bi3+ and Eu3+ ions. These features indicate the potential application prospects of the prepared samples in visualized thermometer or high-temperature safety marking. Furthermore, leveraging the excellent zero-thermal-quenching performance, outstanding acid/alkali resistance, and color stability of CTO:0.04Bi3+/0.16Eu3+ phosphor, a WLED device with a high Ra value of 95.3 has been realized through its combination with commercially available blue and green phosphors, thereby demonstrating the potential application of CTO:0.04Bi3+/0.16Eu3+ in near-UV pumped WLED devices.

Triple-Phosphorescent Gold Nanoclusters Enabled by Isomerization of Terminal Thiouracils in the Surface Motifs

Metal nanoclusters (NCs) hold great promise for expressing multipeak emission based on their well-defined total structure with diverse luminescent centers. Herein, we report the surface motif-dictated triple phosphorescence of Au NCs with dynamic color turning. The deprotonation-triggered isomerization of terminal thiouracils can evolve into a mutual transformation among their hierarchical motifs, thus serving a multipeak-emission expression with good tailoring. More importantly, the underlying electron transfer is thoroughly identified by excluding the radiative and nonradiative energy transfer, where electrons flow from the first phosphorescent state to the last two ones. The findings shed light on finely tailing motifs at the molecular level to motivate studies on customizable luminescence characteristics of metal NCs.

Sb3+/Sm3+ Codoped Cs2NaScCl6 All-Inorganic Double Perovskite: Blue Emission of Self-Trapped Excitons and Red-Emission via Energy Transfer

The lead-free halide perovskites possess nontoxicity and excellent chemical stability, whereas relatively weak luminescence intensity limits their potential in practical applications. Therefore, strengthening the luminescence intensity and expanding application fields are urgent tasks for the development of lead-free halide perovskites. In this paper, antimony-doped Cs2NaScCl6 crystals synthesized by a solvothermal method emit bright, deep blue photoluminescence at 447 nm. The photoluminescence (PL), photoluminescence excitation (PLE), and absorption spectra demonstrate that Sb3+ doping effectively activate the intrinsic "dark self-trapped exciton (STE)," leading to an impressive photoluminescence quantum yield (PLQY) value of 78.31% for 1% Sb3+ doping. Furthermore, the luminescence intensity remains above 92% compared with the fresh sample without secondary phases detected even after 90 days under environmental conditions. To expand the emission spectra, rare-earth Sm3+ is further incorporated into Cs2NaScCl6:1% Sb3+ crystals. The results show that Sb ions not only enhance intrinsic STE luminescence but also serve as sensitizers to boost the red-light emission of Sm3+, leading to a significant 500-fold increase in red emission intensity. Finally, the PLQY reaches a stunning 86.78%. These findings provide valuable insights in the design of Sb ion-doped lead-free double perovskites, broadening the application fields in various optoelectronic devices.

Effectiveness of light-emitting diodes for arsenic and mercury accumulation by Ceratophyllum demersum L.: An innovative advancement in phytoremediation technology

Light Emitting Diodes (LEDs) have emerged as a tool with great potential in the field of phytoremediation, offering a novel approach to enhance the efficiency of plant-based remediation techniques. In this work investigated the influence of LEDs on the phytoremediation of arsenic (As) and mercury (Hg) by Ceratophyllum demersum L., propagated using tissue culture methods. In addition, the biochemical properties of the plants exposed to metal toxicity were examined. Phytoremediation experiments employed concentrations of As (0.01-1.0 mg/L) and Hg (0.002-0.2 mg/L), with application periods set at 1, 7, 14, and 21 days. In addition to white, red and blue LEDs, white fluorescent light was used for control purposes in the investigations. A positive correlation was observed between higher metal concentrations, extended exposure times, and increased metal accumulation in the plants. Red LED light yielded the highest level of heavy metal accumulation, while white fluorescent light resulted in the lowest accumulation level. Examination of the biochemical parameters of the plants, including photosynthetic pigment levels, protein quantities, and lipid peroxidation, revealed a pronouncedly enhanced performance in specimens subjected to red and blue LED illumination, surpassing outcomes observed in other light treatments. The findings of this study introduce innovative avenues for the effective utilization of red and blue LED lights in the realm of phytoremediation research. Thus, the interaction between LEDs, tissue culture, and the phytoremediation process could lead to synergistic effects that contribute to more effective and sustainable remediation strategies.

Ce3+-Activated SrLu2Al3ScSiO12 Cyan-Green-Emitting Garnet-Structured Inorganic Phosphor Materials toward Application in Blue-Chip-Based Phosphor-Converted Solid-State White Lighting

Phosphor-converted white-light-emitting diodes (WLEDs) with superhigh color rendering index (CRI) are the ongoing pursuit of next-generation solid-state lighting. One of the most important challenges is the limited improvement in CRI on account of the absence of a cyan component in the typical commercial combination. Here, a bright broad-band cyan-green-emitting phosphor with cubic garnet structure, SrLu2Al3ScSiO12:Ce3+ (SLASSO:Ce3+), was successfully reported, which can compensate for the absence of cyan cavity in the 480-520 nm blue-green emission region. With 439 nm blue-light irradiation, the as-fabricated SLASSO:Ce3+ phosphor yields a broad-band cyan-green emission with the maximum emission peak positioned at 525 nm and an appropriate full width at half-maximum (fwhm) of 111 nm, capable of providing more cyan emission component without sacrificing green emission. Meanwhile, the optimal SLASSO:2%Ce3+ phosphor features CIE color coordinates of (0.3254, 0.5470) with cyan-green hue, along with a high internal quantum efficiency of up to 93%. Additionally, thermal stability measurements at different temperatures reveal that the luminescence emission intensity of the proposed phosphor retains 44% of its original integral emission intensity at 423 K with respect to room temperature, while also demonstrating an excellent color stability (ΔE = 5.4 × 10-3). This work shows that the highly efficient SLASSO:Ce3+ garnet phosphor can be utilized as a potential cyan-green-emitting phosphor for filling the cyan gap, resulting in the construction of a high-quality warm WLED with high CRI for "human-centric" sunlight-like full-spectrum solid-state illumination.

The synthesis and properties of Ca3 Sc2 Si3 O12 :Ce3+ (CSSG) phosphor are utilized for the development of human-centric lighting light-emitting diodes (HCL-LEDs)

In this study, cerium ion (Ce3+ )-doped calcium scandium silicate garnet (Ca3 Sc2 Si3 O12 , abbreviated CSSG) phosphors were successfully synthesized using the sol-gel method. The crystal phase, morphology, and photoluminescence properties of the synthesized phosphors were thoroughly investigated. Under excitation by a blue light-emitting diode (LED) chip (450 nm), the CSSG phosphor displayed a wide emission spectrum spanning from green to yellow. Remarkably, the material exhibited exceptional thermal stability, with an emissivity ratio at 150°C to that at 25°C reaching approximately 85%. Additionally, the material showcased impressive optical performance when tested with a blue LED chip, including a color rendering index (CRI) exceeding 90, an R9 value surpassing 50, and a biological impact ratio (M/P) above 0.6. These noteworthy findings underscore the potential applications of CSSG as a white light-converting phosphor, particularly in the realm of human-centered lighting.

Cation vacancy-boosted BaZnB4O8:xEu3+ phosphors with high quantum yield and thermal stability for pc-WLEDs

Achieving high luminescent quantum yield and thermal stability of phosphors simultaneously remains challenging, yet it is critical for facilitating high-power white light emitting diodes (WLEDs). Herein, we report the design and preparation of the layered structure BaZnB4O8:xEu3+ (0.10 ≤ x ≤ 0.60) red phosphors with high quantum yield (QY = 76.5%) and thermal stability (82.8%@150 °C) by the traditional solid-state reaction method. The results of XRD and Rietveld refinement show that the presence of Eu3+ ions at Ba2+ sites causes the formation of cation (Zn2+/Ba2+) vacancies in the lattice. The PL and PL decay results reveal that the quenching concentration of BZBO:xEu3+ phosphors is as high as 50%, and the lifetime remains unchanged with Eu3+ concentration due to the unique structure of the host and the cation vacancies generated by the heterovalent substitution. Furthermore, on a 395 nm near-UV chip, a pc-WLED device with exceptional optical performance (CCT = 4415 K, CRI = 92.1) was realized using the prepared BZBO:0.50Eu3+ as a red phosphor. Simple synthesis and excellent performance parameters suggest that the reported BaZnB4O8:xEu3+ phosphors have promising applications in high-power pc-WLEDs. At the same time, it also indicates that cationic vacancy engineering based on heterovalent ion substitution is a potential strategy for improving luminescence quantum yield and thermal quenching performance.

The developments of cyan emitting phosphors to fulfill the cyan emission gap of white-LEDs

Future generations of solid-state lighting (SSL) will prioritize the development of innovative luminescent materials with superior characteristics. The phosphors converted into white light-emitting diodes (white LEDs) often have a blue-green cavity. Cyan-emitting phosphor fills the spectral gap and produces "full-visible-spectrum lighting." Full-visible spectrum lighting is beneficial for several purposes, such as light therapy, plant growth, and promoting an active and healthy lifestyle. The design of cyan garnet-type phosphors, like Ca2LuHf2Al3O12 (CLHAO), has recently been the subject of interest. This review study reports a useful cyan-emitting phosphor based on CLHAO composition with a garnet structure to have a cyan-to-green emitting color with good energy transfer. It could be employed as cyan filler in warm-white LED manufacturing. Due to its stability, ability to dope with various ions suitable for their desired qualities, and ease of synthesis, this garnet-like compound is a great host material for rare-earth ions. The development of CLHAO cyan-emitting phosphors has exceptionally high luminescence, resulting in high CRI and warm-white LEDs, making them a viable desire for LED manufacturing. The development of CLHAO cyan-emitting phosphors with diverse synthesis techniques, along with their properties and applications in white LEDs, are extensively covered in this review paper.

An efficient blue-excitable broadband Y3ScAl4O12:Ce3+ garnet phosphor for WLEDs

Most commercial phosphor-converted white light-emitting diodes (pc-WLEDs) are manufactured with blue LED chips and yellow-emitting Y3Al5O12:Ce3+ (YAG:Ce3+) garnet phosphor, but the lack of blue-green light in the spectrum results in a low color rendering index (CRI). In this paper, we synthesized Y3ScAl4O12:Ce3+ (YSAG:Ce3+) by replacing Al3+ in YAG:Ce3+ with Sc3+. The introduction of Sc3+ with a larger ionic radius through a cation substitution strategy causes lattice expansion, elongation of the Y-O bond, and ultimately a decrease in Ce3+ 5d level crystal field splitting. As a consequence, the emission spectrum undergoes a blue-shift of 10 nm. Furthermore, the YSAG:Ce3+ phosphor exhibits good thermal stability, and its emission intensity at 423 K is about 58% of that at 303 K. Moreover, the analysis of Eu3+ emission spectra demonstrates that the introduction of Sc3+ resulted in a slight reduction of the dodecahedral lattice symmetry. YSAG:Ce3+ effectively compensates for the lack of the blue-green region, and WLEDs with high color rendering index (90.1), low color temperature (4566 K) and high luminous efficiency (133.59 lm W-1) were prepared using the combination of YSAG:0.08Ce3+, CaAlSiN3:Eu2+ and 450 nm blue chips. These findings indicate that YSAG:Ce3+ garnet phosphor has potential to be used in high quality WLEDs.

Vinylene-Linked Emissive Covalent Organic Frameworks for White-Light-Emitting Diodes

Covalent organic frameworks (COFs) have gained considerable attention due to their highly conjugated π-skeletons, rendering them promising candidates for the design of light-emitting materials. In this study, we present two vinylene-linked COFs, namely, VL-COF-1 and VL-COF-2, which were synthesized through the Knoevenagel condensation of 2,4,6-trimethyl-1,3,5-triazine with terephthalaldehyde or 4,4'-biphenyldicarboxaldehyde. Both VL-COF-1 and VL-COF-2 exhibited excellent chemical and thermal stability. The presence of vinylene linkages between the constituent building blocks in these COFs resulted in broad excitation and emission properties. Remarkably, the designed VL-COFs demonstrated bright emission, fast fluorescence decay, and high stability, making them highly attractive for optoelectronic applications. To assess the potential of these VL-COFs in practical devices, we fabricated white-light-emitting diodes (WLEDs) coated with VL-COF-1 and VL-COF-2. Notably, the WLEDs coated with VL-COF-1 achieved high-quality white light emission, closely approximating standard white light. The promising performance of VL-COF-coated WLEDs suggests the feasibility of utilizing COF materials for stable and efficient lighting applications.

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.

High-Efficiency Ce3+ Activated Orthorhombic Lanthanide Silicate Blue Phosphors for Plant Growth Lighting

Plant growth can be controlled and freed from natural environmental interference through indoor plant cultivation. Artificial light sources with better quality are required to promote indoor plant growth. In this study, we used a simple high-temperature solid-state reaction to synthesize high-efficiency Ce3+-activated NaGdSiO4 (NGSO) phosphors. X-ray diffraction and Rietveld refinement were performed to determine the detailed crystal structure of the NGSO:Ce3+ phosphors. The morphology of NGSO:Ce3+ and the elemental state of Ce3+ were measured and analyzed. Under near-ultraviolet (n-UV) light excitation, the Ce3+-activated NGSO phosphors exhibit a broad emission band from 375 to 500 nm, and their emission peaks are at approximately 401 nm. This asymmetrical blue emission band is caused by the spin-allowed 5d → 4f transition of Ce3+ and overlaps well with the blue absorption region of carotenoids and chlorophyll. The temperature-dependent luminescence spectra were utilized to assess the thermal stability of NGSO:Ce3+. The external quantum efficiency (EQE) was measured to be 60.91%, and the internal quantum efficiency (IQE) was measured to be 73.39%. A blue LED device assembled from the NGSO:Ce3+ phosphor has demonstrated the application potential in accelerating plant growth.

A graphitic-C3N4 derivative containing heptazines merged with phenyls: synthesis, purification and application as a high-efficiency metal-free quasi-green phosphor for white LEDs

Because rare-earth elements are scarce, expensive, and unsustainable, it is of great significance to develop rare-earth-free (even metal-free) luminescent materials as phosphors for LEDs. Here, a graphitic-C₃N₄ (g-C₃N₄) derivative containing some heptazines merged with phenyls has been synthesized via thermal polymerization of melamine and quinazoline-2,4(1H,3H)-dione at an optimal mole ratio of 18 : 1. In comparison with g-C₃N₄ synthesized from melamine only, the photoluminescent (PL) emission colour changed from blue to green, the maximum emission wavelength (λ _em,max) changed from 467 nm to 508 nm, and the PL quantum yield (PLQY) increased from 8.0% to 24.0%. It was further purified via vacuum sublimation, and a product with yellowish green emission (λ _em,max = 517 nm) and PLQY up to 45.5% was obtained. This sublimated product had high thermal stability and low thermal quenching; its thermal decomposition temperature was as high as 527 °C, and its relative PL emission intensity at 100 °C was 90.8% of that at 20 °C. Excited by blue light chips (λ _em,max ≈ 460 nm), cold, neutral and warm white LEDs can be fabricated using the sublimated product and orange-emitting (Sr,Ba)₃SiO₅:Eu²⁺ as phosphors. The good performances of these white LEDs (for example, the CIE coordinates, color rendering index and correlated color temperature were (0.31, 0.33), 84.4 and 6577 K, respectively) suggest that the low-efficiency blue-emitting g-C₃N₄ had been successfully converted into a high-efficiency metal-free quasi-green phosphor.

Modulation of Bi3+ luminescence from broadband green to broadband deep red in Lu2WO6 by Gd3+ doping and its applications in high color rendering index white LED and near-infrared LED

Phosphors that exhibit tunable broadband emissions are highly desired in multi-functional LEDs, including pc-WLEDs and pc-NIR LEDs. In this work, broadband emissions were obtained and modulated in the unexpectedly wide spectral range of 517-609 nm for (Lu_0.99-xGd_xBi_0.01)₂WO₆ phosphors by tuning the Gd³⁺ content (x = 0-0.99). The effects of Gd³⁺ doping on phase constituents, particle morphology, crystal structure, and photoluminescence were systematically investigated. Broadband green emission was obtained from Gd³⁺-free (Lu_0.99Bi_0.01)₂WO₆ phosphors (x = 0), whose emission intensity was enhanced by 50% with 5 at% Gd³⁺ (x = 0.05). The phase transition happened when x > 0.50 and the broadband red-NIR emission was obtained when x = 0.75-0.99. Three luminescence centers were proved to be responsible for the broadband green emissions via crystal structure, spectral fitting and fluorescence decay analysis. A pc-WLED with a high color rendering index (R_a = 91.3), a stable emission color, and a low color temperature (3951 K) was fabricated from the (Lu_0.94Gd_0.05Bi_0.01)₂WO₆ broadband green phosphor, and an LED device that simultaneously emits high color rendering index white light and NIR light was obtained with the (Gd_0.99Bi_0.01)₂WO₆ broadband red-NIR phosphor. Night vision and noninvasive imaging were also demonstrated using the latter LED device.

Highly-efficient Eu2+-activated Sr8Si4O12Cl8 cyan-emitting phosphors with zero-thermal quenching luminescence for versatile applications

To settle the problem of phosphors with unsatisfactory luminescence efficiency and serious thermal quenching, Eu²⁺-activated Sr₈Si₄O₁₂Cl₈ cyan-emitting phosphors were designed. Excited at 387 nm, a dazzling cyan emission located at 492 nm is observed in the resultant phosphors and its maximum intensity is obtained when the Eu²⁺ content is 4 mol%. Moreover, the zero-thermal quenching luminescence, even when the temperature is 503 K, the integrated emission intensity still maintains 106% of its starting value at 303 K, is realized in resultant phosphors because of the efficient energy transfer from defect levels to Eu²⁺, which is confirmed by the thermoluminescence spectrum. The electroluminescence spectrum of the packaged white light-emitting diode (white-LED) is detected and it is found to possess a high color rendering index (91.0), low correlated color temperature (4875 K) and a superior luminous efficiency (68.7 lm W^-1), implying that the developed phosphors can be adopted as cyan-emitting components to fulfill the cyan gap and realize a full spectrum white-LED. Furthermore, the cathodoluminescence (CL) performance of samples is also studied, in which its CL emission intensity is greatly impacted by the accelerating voltage and the filament current. Additionally, using the synthesized phosphors, various types of patterns are designed for use in information encryption. These achievements reveal that the Eu²⁺-activated Sr₈Si₄O₁₂Cl₈ phosphors are multifunctional cyan-emitting candidates for full spectrum white-LED, field-emission display and anti-counterfeiting applications.

Structure and Luminescence Studies of a Ce3+-Activated Ba5La3MgAl3O15 Green-Emitting Phosphor

Novel green-emitting Ba₅La₃MgAl₃O₁₅:Ce³⁺ (BLMAO:Ce³⁺) is successfully obtained by a solid-state reaction. In this study, BLMAO, which is inspired from the Ba₆La₂A_1.5Fe_2.5O₁₅ crystal structure, shows a green emission approximately peaked around 500 nm under near-ultraviolet light excitation at 412 nm by Ce³⁺ doping. Moreover, internal and external quantum efficiencies of BLMAO:0.02Ce³⁺ are found to be 27 and 22%, respectively. The emission peak deconvolution and Dorenbos model calculation reveal that the Ce³⁺ ion occupies on two different crystallographic sites. The potential of BLMAO:Ce³⁺ for phosphor-converted white LEDs (pc-wLEDs) is systematically evaluated from the results of Rietveld refinement and luminescence measurement.

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.

Thermal Quenching Mechanism of Metal-Metal Charge Transfer State Transition Luminescence Based on Double-Band-Gap Modulation

Bi³⁺-related metal-to-metal charge transfer (MMCT) transition phosphors are expected to become a new class of solid-state luminescent materials due to their unique broadband long-wavelength emission; however, the main obstacle to their application is the thermal quenching effect. In this study, one novel thermal quenching mechanism of Bi³⁺-MMCT transition luminescence is proposed by introducing electron-transfer potential energy (ΔE_T). Y_0.99V_1-xP_xO₄:0.01Bi³⁺ (YV_1-xP_xO₄:Bi³⁺) is used as the model; when the band gap of the activator Bi³⁺ increases from 3.44 to 3.76 eV and the band gap of the host YV_1-xP_xO₄ widens from 2.75 to 3.16 eV, the electron-transfer potential energy (ΔE_T) decreases and the thermal quenching activation energy (ΔE) increases, which result in the relative emission intensity increasing from 0.06 to 0.64 at 303-523 K. Guided by density functional calculations, the thermal quenching mechanism of the Bi³⁺-MMCT state transition luminescence is revealed by the double-band-gap modulation model of the activator ion and the matrix. This study improves the thermal quenching theory of different types of Bi³⁺ transition luminescence and offers one neo-theory guidance for the contriving and researching of high-quality luminescence materials.

Nonstoichiometric LaO0.65F1.7 Structure and Its Green Luminescence Property Doped with Bi3+ and Tb3+ Ions for Applying White UV LEDs

Red–green–blue phosphors excited by ultraviolet (UV) radiation for white light LEDs have received much attention to improve the efficiency, color rendering index (CRI), and chromatic stability. The spectral conversion of a rare-earth ion-doped nonstoichiometric LaO_0.65F_1.7 host was explored with structural analysis in this report. The nonstoichiometric structure of a LaO_0.65F_1.7 compound, synthesized by a solid-state reaction using La₂O₃ and excess NH₄F precursors, was analyzed by synchrotron X-ray powder diffraction. The crystallized LaO_0.65F_1.7 host, which had a tetragonal space group of P4/nmm, contained 9- and 10-coordinated La³⁺ sites. Optical materials composed of La_1−p−qBi_pTb_qO_0.65F_1.7 (p = 0 and 0.01; q = 0–0.2) were prepared at 1050 °C for 2 h, and the single phase of the obtained phosphors was indexed by X-ray diffraction analysis. The photoluminescence spectra of the energy transfer from Bi³⁺ to Tb³⁺ were obtained upon excitation at 286 nm in the nonstoichiometric host lattice. The desired Commission Internationale de l’Eclairage (CIE) values of the phosphors were calculated. The intense green La_0.89Bi_0.01Tb_0.1O_0.65F_1.7 phosphor with blue and red optical materials was fabricated on a 275 nm UV-LED chip, resulting in white light, and the internal quantum efficiency, CRI, correlated color temperature, and CIE of the pc LED were characterized.

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.

Dazzling Red-Emitting Europium(III) Ion-Doped Ca2LaHf2Al3O12 Garnet-Type Phosphor Materials with Potential Application in Solid-State White Lighting

Bright red-emitting phosphors with high color purity and high photoluminescence quantum yield (PLQY) are highly demanded for the fabrication of high-performance warm-white light-emitting diodes (LEDs). Herein, we demonstrated a novel efficient Eu³⁺-activated Ca₂LaHf₂Al₃O₁₂ garnet phosphor with excellent luminescence properties for near-ultraviolet (near-UV) excited warm-white LEDs. The Ca₂LaHf₂Al₃O₁₂:Eu³⁺ phosphors exhibited an intense excitation spectrum in the near-UV region with a maximum around 394 nm, and they produced dazzling red luminescence peaking at 592, 614, 659, and 711 nm due to the ⁵D₀ → ⁷F_J (J = 1-4) transitions of Eu³⁺ ions when the excitation wavelength was set at 394 nm. Luminescent properties have been studied as a function of Eu³⁺ doping concentration, and the highest emission intensity was achieved at 50 mol % Eu³⁺, while the dipole-dipole interaction brought the concentration quenching effect. The Ca₂LaHf₂Al₃O₁₂:50%Eu³⁺ sample exhibited CIE chromaticity coordinates of (0.6419, 0.3575) with a color purity of 92.7%, and its PLQY was measured to be 64%. The thermal stability and activation energy of Ca₂LaHf₂Al₃O₁₂:50%Eu³⁺ phosphors were also discussed and analyzed. Finally, we made a near-UV chip-based white LED device in which the Ca₂LaHf₂Al₃O₁₂:50%Eu³⁺ phosphor was utilized as a red ingredient. A bright warm-white light emission was realized from this LED device under 80 mA driving current, accompanied by a high color rendering index (CRI) of 88.3, a low correlation color temperature of 3853 K, and good CIE chromaticity coordinates of (0.3909, 0.3934). These results revealed that these red-emitting Ca₂LaHf₂Al₃O₁₂:Eu³⁺ phosphors have promising application prospect in near-UV-excited warm-white LEDs with high a CRI.

Improving the luminescence property of the novel yellow-emitting phosphor SrLa2Sc2O7:Bi3+ with charge compensators (Li+, Na+, K+) and its application in NUV-based white LEDs

In this work, a novel yellow-emitting phosphor SrLa2Sc2O7:Bi3+ was synthesized by high temperature solid-state method, ranging from 400 nm to 800 nm under near-ultraviolet (NUV) excitation and the full width at half maximum (FWHM) of up to 180 nm.

A novel red-emitting phosphor with an unusual concentration quenching effect for near-UV-based WLEDs

An unusual concentration quenching effect is caused by the anisotropic distribution of quenching centers in GdGaTi2O7:Eu3+.