Warm White Light-emitting Diodes Research Articles

NUV-pumped luminescence of thermally stable samarium-activated alkali metal borophosphate phosphor

Exploring outstanding rare-earth activated inorganic phosphors with good thermostability has always been a research focus for high-power white light-emitting diodes (LEDs). In this study, we report a Sm3+-activated KNa4B2P3O13 (KNBP) powder phase. Its particle morphology, photoluminescence properties, concentration quenching mechanism, thermal quenching mechanism, and chromatic properties are demonstrated. Upon the near-ultraviolet (NUV) irradiation of 402 nm, the powder phase exhibits orange-red visible luminescence performance, originating from typical 4G5/2→6HJ/2 (J = 5, 7, 9) transitions of Sm3+. Importantly, the photoluminescence performance has good thermostability, low correlated color temperature (CCT), and high color purity (CP), indicating its promising application in the NUV-pumped warm white LEDs.

Green synthesis, luminescent properties and application for WLED of flower-like K2LiAlF6:Mn4+ phosphor

Chrysanthemum-like K 2 LiAlF 6 :Mn 4+ phosphors were synthesized by simple co-precipitation method without using HF. The K 2 LiAlF 6 :Mn 4+ phosphor can be effectively excited through blue light at 465 nm, then produces sharp red-light emission near 634 nm. The luminescence quenching of Mn 4+ is caused by the d-d interaction between Mn 4+ ions. The effects of surfactant and lithium source on the luminescent properties of K 2 LiAlF 6 :Mn 4+ phosphors were discussed. Mn 4+ is located in a strong crystal field environment in the K 2 LiAlF 6 matrix and its emission mechanism is discussed. Warm white light emitting diode (WLED) device, which is fabricated by coating a certain proportion mixture of yellow YAG:Ce 3+ phosphor and red K 2 LiAlF 6 :5%Mn 4+ phosphor on the blue GaN chip, has low correlation color temperature (CCT = 3588 K), high color rendering index (R a = 90.8) and good electroluminescence stability under different currents. These properties illustrate that K 2 LiAlF 6 :5%Mn 4+ phosphor is a promising red light emitting material. • Chrysanthemum-like K 2 LiAlF 6 :Mn 4+ were prepared by using low-toxic NH 4 F and HCl instead of highly toxic HF. • The effects of reaction conditions on luminous characteristics of K 2 LiAlF 6 :Mn 4+ were discussed. • K 2 LiAlF 6 :Mn 4+ phosphors have excellent photoelectric performance for LED application.

Small molecule organic solar cells toward improved stability and performance for Indoor Light Harvesting Application

In this work, we fabricate, characterize and present a stability study of p-DTS(FBTTh 2 ) 2 :PC 70 BM inverted organic solar cells (iOSCs) with two different solution-processed electron transport layers (ETLs), PFN and ZnO, under indoor light and AM 1.5 G illumination spectrum. A warm white color light-emitting diode was used as the indoor light source. Under the luminance of 1000 lux, a maximum power conversion efficiency (PCE) of 10.85% and maximum power density (MPP) of 45.1 μW/cm 2 were obtained for cells with PFN as ETL. After 1536 h of constant indoor light illumination, the PCE remained above 70% of the original value. The best stability of encapsulated devices, under AM 1.5 illumination spectrum was also observed for these cells, which still maintained a PCE above 60% after 6000 h. Performance of small-molecule organic solar cells for Indoor Light Harvesting Application. PFN as electron transport layer for inverted solution-processed small-molecule organic solar cells (SM-iOSC). 1.5 times longer lifetime of encapsulated SM-iOSC versus currently used inverted polymer solar cells (iPSC). Reduced S-shape deformation in the JV curves of HIZO-iOSC vs. PFN-iOSC. Degradation analysis by the solar cells equivalent circuit model.

Design and fabrication of a downlight luminaire with a dual frusto-conical reflector.

A design method and corresponding fabrication procedures are proposed for a dual frusto-conical reflector of a downlight luminaire. The profile of the dual frusto-conical reflector consists of two flat-slant reflective surfaces with slightly different slopes. The optimum dual frusto-conical reflector can be obtained with the proposed design method. The finished product of the dual frusto-conical reflector is fabricated by a 3D printer and followed by surface polishing and reflection paint spraying. The measurement results show that luminaires exhibited 70% optimum illuminance confined within an illumination area of 1.8m2, and the optimum illumination intensity is at 252 lux. The optimum efficiency of the proposed luminaire can reach 158 lm/W for normal-white light-emitting diode (LED) and 119 lm/W for warm-white LED, respectively.

High luminescent thermal stability and water resistance of K2SiF6:Mn4+@CaF2 red emitting phosphor

K2SiF6:Mn4+ (KSF:Mn4+), as an efficient red-emitting phosphor, has a promising application in WLEDs (white light-emitting diodes). However, poor moisture resistance performance still hinders its deeper commercialization. Here, KSF:Mn4+@ CaF2 with high water resistance and luminescent thermal stability has been prepared though H2O2-free hydrothermal method and surface coating process. Both KSF:Mn4+ and KSF:Mn4+@CaF2 all have high luminescent thermal stability, due to negative thermal quenching (NTQ) effect. Mechanism of the NTQ has been discussed and suggested as thermal-light energy conversion mechanism. Compared with KSF:Mn4+, water resistance of KSF:Mn4+@CaF2 is greatly improved by coating of CaF2, because the outer shell of CaF2 can effectively prevent the [MnF6]2- group on the surface of the phosphor from being hydrolyzed into MnO2. The results of water resistance test shows that after immersing in water for 360 min (6 h), luminescent intensity of the uncoated product drops to 41.68% of the initial one, while that of the coated product remains to have 88.24% of its initial one. Warm white light with good luminescent performances (CCT = 3956 K and Ra = 89.3) is got from prototype WLEDs assembled by using the optimal coated sample. The results suggest that the optimal coated sample has potential application in blue-based warm WLEDs.

Modified α-Al2O3 wafer: Enhance the stability of perovskite quantum dots with wide colour gamut for white light-emitting diodes

Recently, perovskite has received extensive attention due to their excellent photoelectric properties, while the instability of perovskite quantum dots (PQDs) has always troubled us. Herein, we proposed a simple coating mechanism to protect PQDs. Using oleic acid (OA) for etching α-Al2O3 wafer to make the surface appear pore structure, and the PQDs was coated within the modified α-Al2O3 wafer, thereby improving the stability of PQDs. The CsPbX3@α-Al2O3 composite material can achieve the emission of blue-green–red (436 nm to 636 nm) through adjustable luminescence wavelength. The photoluminescence (PL) intensity of CsPbBr3@α-Al2O3 composite material exposure to the air after 28 days can maintain over 50%. It is worth noticing that the photoluminescent quantum yield (PLQY) of CsPbBrI2@α-Al2O3 composite material can reach 58%, the colour purity of CsPbBr3@α-Al2O3 and CsPbBrI2@α-Al2O3 achieve 97.1% and 99.8%, respectively. It was due to the high colour purity of the composite materials can the selected CIE colour coordinate monochromatic light encompassed 114% of NTSC colour gamut. Moreover, the warm white light-emitting diode (WLED) yielded bright natural white light and showed the luminous efficiency (LE) of 86.58 lm/W, colour rendering index (CRI) of 86.9, correlated colour temperature (CCT) of 4602 K. The LE and CRI reaches a relatively balanced value, which showed that this composite material has a certain development prospect in the WLED field.

Microwave-hydrothermal synthesis and investigation of Mn-doped K2SiF6 microsize powder as a red phosphor for warm white LEDs

Microsize powder of Mn-doped potassium hexaflourosilicate (PFS, K2SiF6) phosphor has been synthesized using the microwave-hydrothermal (MWHT) method, a new approach for obtaining this material. Special attention has been paid to the identification of the valence states for Mn doping ions using EPR and XANES techniques. Although photoluminescence results reveal luminescence properties typical for Mn4+ ions, the XANES spectra show the presence of Mn ions in various valence states (+2 to +4). The analysis of the temperature dependence for the Mn4+ integrated luminescence intensity and luminescence decay time has shown that the MWHT synthesis provides better performance of the PFS phosphor compared to that of commercially available PFS phosphors in respect of higher thermal stability because of improved crystallinity and lower concentration of defects. It has been revealed that above 500 K, Mn4+ luminescence decay becomes non-exponential due to the energy transfer to defect quenching centers. Repeated thermal treatment of microparticles up to 700 K results in considerably changed thermal quenching parameters due to the transformation of K2SiF6 into the K3SiF7 phase. The latter compound doped with Mn4+ shows spectral properties very similar to those of K2SiF6:Mn4+ but demonstrates better thermal stability and shorter decay time of Mn4+ luminescence at normal conditions which can make the red-emitting K3SiF7:Mn4+ phosphor a promising candidate for application in wLEDs.

A novel Eu3+-doped ScCaO(BO3) red phosphor for tricolor-composited high color rendering white light

Exploration of novel red emitting phosphors containing Eu3+ ions is an everlasting topic in the field of luminescent materials due to the application requirement of warm white light-emitting diodes. In this work, the Eu3+-doped ScCaO(BO3) phosphors were synthesized though the high temperature solid-state reaction method. The phase purity and detail information on crystal structure were obtained by X-ray diffraction (XRD) and the technology of Rietveld XRD refinement. Scanning electron microscopy (SEM) was applied to check the particle morphology and EDS mapping was taken to analyze element distributions. Optical properties of the phosphors were studied by measuring the steady-state excitation and emission spectra and also the transient luminescence decays. The emission spectra of ScCaO(BO3):Eu3+ majorly consisted of 5D0-7F1, 7F2 and 7F4 transitions, covering the orange (582–605 nm), red (605–635 nm) and deep red (690–720 nm) spectral regions. The doping concentration of Eu3+ ions was optimized to 12% to maximize the optical performance of the red emitting phosphors, whose CIE coordinate and fluorescent lifetime were (0.6458, 0.3537) and 1.516 ms, respectively. The investigation of the thermal quenching behavior of the ScCaO(BO3):0.12Eu3+ phosphor reveals that the emission intensity of Eu3+ at 400 K can maintain 68.98% of that at room temperature due to the existence of the thermal activation energy of 0.258 eV. Using such a red-emitting material, the prototype warm white LED device with the CIE coordinate of (0.3262, 0.3363), color rendering index of 86.1 and correlated color temperature of 5871 K can be obtained by combining with the blue emitting BaMgAl10O17:Eu2+ and green emitting Zn2SiO4:Mn2+ phosphors and coating all three on a near-UV LED chip. All the results demonstrate that the ScCaO(BO3):0.12Eu3+ phosphor can sever as a potential red emitting candidate for near-UV excited warm WLEDs.

Octupolar Acrylonitrile-Bridged 2D-Conjugated Polymers Enable Bright Far-Red Emission with Intense Two-Photon Absorption via Alkoxylation Chemistry.

Herein, alkoxylation chemistry is introduced as a "one-stone-three-birds" solution for exploring a new family of highly-fluorescent octupolar 2D-conjugated organic polymers/frameworks (OCOPs/OCOFs) combining far-red emission, high fluorescence quantum yield (QY), and strong two-photon absorption (TPA). Both alkoxy-substituted OCOP and OCOF comprising acrylonitrile-bridged strongly-coupled donor3-(acceptor core) chromophores densely packed in either disordered or ordered forms, exhibit significantly redshifted emission. They produce high QY of 22.2% and 27.8% in tetrahydrofuran, large TPA cross section of 600 and 1124 GM, and 2-3 folds and 15-30 folds that of non-alkoxylate amorphous counterpart respectively. Combined theoretical and experimental studies reveal unique "one-stone-three-birds" role of the alkoxylation in realizing red-shifted-emission, improved QY and TPA enabled by inducing steric hindrance effect for weakened π-π stacking, and triggering p-π conjugation effect for electronically engineering octupolar chromophores, while the crystalline engineering enables enforced coplanarity conformation and improved π-electron delocalization for further improved QY and TPA. The robust and biocompatible pentoxy-substituted polymer can be used not only as metal-free red-emissive phosphor for efficient warm white light-emitting diodes, but also as efficient two-photon fluorescence probes for bio-imaging.

Influence of Dy3+ ion concentration on photoluminescence and energy transfer mechanism of promising KBaScSi3O9 phosphors for warm white LEDs

A novel white light emitting silicate-based phosphor of Dy3+ activated KBaScSi3O9 (xDyKBS) was prepared by a conventional solid state method. Powder X-ray diffraction patterns represent the pure phase of synthesized materials that was formed with monoclinic structure. The metal–ligand bonding nature and electronic band structure have been examined optical absorption spectra. The luminescence emission curves of the silicate phosphors display an intense yellow emission peak at 579 nm and a blue emission peak at 491 nm. Among the emission bands, the band observed in the yellow region due to 4F9/2→6H13/2 transition was found to be higher intensity. The radiative parameters like transition probabilities (AR), branching ratios (βR) and stimulated emission cross-section (σPE) values were calculated using Judd–Ofelt parameters and refractive index values for the observed transitions in emission spectra. The life time measurements were made for 4F9/2 → 6H13/2 transition of all the studied samples by keeping an excitation at 350 nm and emission at 579 nm and decay curves were fitted to bi-exponential fitting method. The CCT values obtained from the color coordinates suggested that present xDyKBS phosphors can emit warm and neutral white light depending upon the dopant concentration under near-UV excitation. Our results demonstrated that the optimum concentration 0.05DyKBS phosphor can be successfully utilized as a promising and potential candidate for various innovative photonic applications like warm white LEDs, solar cells, optical sensors and lasers.

Bismuth‐activated, narrow‐band, cyan garnet phosphor Ca3Y2Ge3O12:Bi3+ for near‐ultraviolet‐pumped white LED application

AbstractHerein, a novel Bi3+‐activated Ca3Y2Ge3O12 (CYGO) narrow‐band cyan‐emitting phosphor was synthesized. It can be excited from 320–420 nm, and the strongest excitation peak is located at 370 nm, which is suitable for current near‐ultraviolet (NUV) chips perfectly. The full width at half maximum is at 52 nm. By analyzing the crystal structure of the sample, we infer that the Bi3+ ions replace the Y3+ site to form a highly symmetrical BiO6 octahedron. The time‐resolved photoluminescence (TRPL) spectra of CYGO: Bi3+ reveal that the only a single emission center exists in the host lattice. A warm white light–emitting diode (WLED) device with a low correlated color temperature (3148 K) and a high color rendering index (90.2) was fabricated by using the as‐prepared sample, and the significant thermal stability of CYGO: Bi3+ guarantees its potential application in WLEDs. It is verified that the structure with only one crystallographic Y site for Bi3+ dopant occupation and highly symmetrical and dense structure is conducive to realize narrow‐band emission, which will provide experience for researchers to explore more Bi3+‐activated phosphors used for high‐end lighting.

Highly thermally stable Dy3+/Sm3+ co-doped Na5Y9F32 single crystals for warm white LED

The optical behavior and thermal stability of Na5Y9F32 single crystals doped with fixed 1 mol% Dy3+ and various Sm3+ content grown by Bridgman technique were investigated by means of the fluorescence spectra, decay curves and temperature-dependent emission spectra. Upon 365 nm excitation, the emission color shifted from cool white emission to warm white emission as the Sm3+ concentration rise from 0 mol% to 1.6 mol%, in which the CIE coordinates experienced from (0.3445, 0.3888) to (0.3727, 0.3695) and the values of correlated color temperature (CCT) descended from 5114 K to 4174 K. The energy transfer (ET) from Dy3+ to Sm3+ identified by decay curves with emission spectra played significant effect on the change of emission color and the maximum energy transfer efficiency (ETE) was calculated to be 44.5% from the measured decay curves. Based on the Dexter's energy transfer formula, the mechanism of ET from Dy3+ to Sm3+ was determined as a dipole-dipole interaction. The down-conversion internal quantum yield (QY) of 1 mol% Dy3+/0.8 mol% Sm3+ co-doped Na5Y9F32 single crystal was estimated to be ~15.9%. When excited by 365 nm, Dy3+/Sm3+ co-doped Na5Y9F32 single crystals displayed excellent thermal stability deducing from the temperature-dependent emission spectra, in which the normalized emission intensity can still maintain 83% at 423 K. These results indicated that Dy3+/Sm3+ co-doped Na5Y9F32 single crystal held potential application prospect in warm white light-emitting diodes (w-LEDs.)

Near-unity blue-orange dual-emitting Mn-doped perovskite nanocrystals with metal alloying for efficient white light-emitting diodes

The tunable dual-color emitting Mn2+ doped CsPbCl3-xBrx nanocrystals (NCs) with near-unity photoluminescence quantum yield (PL QY) were synthesized through post-treatment of metal bromide at room temperature for fabrication of efficient warm white light-emitting diodes (WLEDs). Especially, the CdBr2 treated blue-orange emitting Mn doped NCs with various Mn/Pb molar feed ratios exhibit higher PL QY of 97% and longer Mn2+ PL lifetime of 0.9 ms. It is surprisingly found that the X-ray diffraction peak at 31.9° is almost not changed with increasing Br composition, meaning formation of metal alloying due to incorporation of amount of divalent cation in NCs. The strong and stable Mn2+ PL at temperature ranging from 80 K to 360 K are revealed and the temperature-dependent energy transfer efficiencies in Mn2+ doped CsPbCl1.5Br1.5 NCs are obtained. The enhancement mechanism of Mn2+ PL QY was attributed to improved energy transfer from exciton to Mn2+ d–d transition and suppressed defect state density after post-treatment. The efficient warm WLEDs with color rendering index of 90 and luminous efficacy of 92 lm/W at 10 mA were fabricated by combining blue-orange dual-emitting Mn2+ doped CsPbCl3-xBrx@SiO2 and green emissive CsPbBr3@SiO2 NCs with violet GaN chips.

New Mg2+/Ge4+-Stabilized Gd3MgxGexAl5-2xO12:Ce Garnet Phosphor with Orange-Yellow Emission for Warm-White LEDs (x = 2.0-2.5).

By stabilization of the Gd3Al5O12 garnet by replacing 80% or more of Al3+ with Mg2+/Ge4+ pairs, a series of new orange-yellow-emitting Gd3MgxGexAl5-2xO12:Ce (x = 2.0-2.5) phosphors were successfully developed for potential application in warm-white-light-emitting diodes (WLEDs). Rietveld structure refinement proved that Mg2+ first substitutes the octahedral Al3+ ion, followed by the replacement of the tetrahedral Al3+ together with Ge4+. The band structure of the x = 2.0 typical garnet was analyzed via density functional theory (DFT) calculations. The incorporation of an increasing content of Mg2+/Ge4+ was experimentally shown to narrow the band gap and expand the unit cell of the garnet host and blue shift the emission/excitation wavelength and shorten the fluorescence lifetime of Ce3+. The photoluminescence behaviors were rationalized by considering the influence of Mg2+/Ge4+ on the crystal structure, band structure, and local coordination. An LED lamp fabricated by combining the (Gd2.97Ce0.03)Mg2Ge2AlO12 optimal phosphor with a 450 nm-emitting InGaN blue LED chip exhibited a color-rendering index of 71.6, luminous efficacy of 16.1 lm/W, and a low correlated color temperature of 2201 K under a driving current of 20 mA, indicating that phosphor may have potential application in warm WLEDs.

Broadband emission of Lu3Mg2GaSi2O12: Ce3+, Sm3+ phosphors and their potential application for w-LEDs

Herein, Lu3Mg2GaSi2O12: Ce3+/Sm3+ (LMGS) phosphors with a garnet structure were synthesized by a high-temperature solid-phase reaction method, and their potential application in w-LEDs was evaluated. In this study, the crystal structure of the phosphor was determined using the Rietveld method and XRD pattern analysis, while the luminescence performance was characterized by the relevant PL spectrum, and then, the energy transfer (ET) mechanism was explored. When subjected to an excitation at a wavelength of 450 nm, the introduction of Sm3+ ions into LMGS: 0.015Ce3+ broadens the broadband emission of Ce3+ ions owing to the co-excitation and ET of Ce3+ and Sm3+. A continuous and controlled variation in the Sm3+ doping concentration facilitates the tuning of color coordinate from green to yellow. The maximum Ce3+→Sm3+ energy transfer efficiency of the sample was 55.64 %. From the viewpoint of practical applications, the sample exhibited excellent thermal stability and water resistance. After combining the LMGS: 0.015Ce3+, 0.03Sm3+ sample with a commercial red phosphor and a blue chip, a warm white LED with a color rendering index of 86.6 and color temperature of 3592 K can be obtained.

7종 형광체 스펙트럼 조합과 Blue LED의 최고파장 및 반치전폭 변화에 따른 S/P Ratio와 연색특성 시뮬레이션 연구

Recently, interest in convenience facilities for road safety and urban aesthetic conditions increased needs to improve visibility and color recognition of night road lightings. To meet the needs, scotopic/photopic(S/P) ratio and color rendering properties, such as color rendering index (CRI), color fidelity (RSUBf/SUB), color gamut (RSUBg/SUB), and color quality scale (QSUBa/SUB) should be considered for outdoor lighting products. It is well known that S/P ratio and CRI are in trade-off relation and, therefore, it is important to optimize them to certain levels through color combinations. In this paper, optimization of phosphor converted LED with a blue LED and 7 phosphors was performed by simulation of changing peak wavelength and full width at half maximum (FWHM) of a blue LED with combinations of 7 phosphors. The results showed that color rendering properties of RSUBa/SUB≥82, RSUB9～14/SUB≥76, RSUB9～12/SUB≥82, QSUBa/SUB≥95, RSUBf/SUB≥89, RSUBg/SUB≥100, and S/P ratio values were increased by 0.29∼0.61 and 0.22∼0.5 compared to those of the typical warm white LED and cool white LED suggested in the IES (Illuminating Engineering Society) TM (Technical Memorandum) 12-12.

A new single-phase NaBi(WO4)2:Dy3+, Eu3+ phosphor with excellent thermal stability for NUV-excited warm white LEDs

A variety of Dy3+ single-doped and Dy3+, Eu3+ co-doped NaBi(WO4)2 phosphors were synthesized by the high temperature solid state method. The XRD patterns and Rietveld refinement measurement were operated to identify the crystalline phases. When the NaBi(WO4)2: 0.08Dy3+, yEu3+ phosphors were excited by 352 nm light, the energy transfer efficiency can be reach to 72.576% and the type of energy transfer mechanism was dominated by the dipole-dipole interaction. The thermal stability of specific NaBi(WO4)2: 0.08Dy3+, 0.1Eu3+ phosphor was tested and the PL emission intensity at 423 K drops to about 77.2% of that at 303 K, and the warm white light can be obtained after varying the Eu3+ ion concentration. Aforementioned results manifest that these as-prepared samples are expected to be the potential single-phase phosphors used in the areas of solid state lighting.

Utilizing energy transfer strategy to produce efficient green luminescence in Ca2LuHf2Al3O12:Ce3+,Tb3+ garnet phosphors for high-quality near-UV-pumped warm-white LEDs

White light-emitting diodes (LEDs) are widely used in lighting and display devices, and the exploration of phosphors with excellent luminescence performance and good stability is the key to the development of white LEDs. In this work, we reported novel near-UV-excited green-emitting Ca2LuHf2(AlO4)3:Ce3+,Tb3+ garnet phosphors with efficient Ce3+ → Tb3+ energy transfer. The CLHA:Ce3+,Tb3+ green phosphors were successfully synthesized by a high-temperature solid-state method, and the phosphors were characterized by X-ray diffraction, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, elemental mapping, photoluminescence excitation and photoluminescence spectra, the Commission International de I’Eclairage (CIE) chromaticity coordinates, quantum efficiency and temperature-dependent emission spectra. Due to the spin-allowed 4f → 5d transition of Ce3+ ions, the CLHA:Ce3+,Tb3+ phosphors exhibited a strong broad excitation band in the 300–470 nm near-ultraviolet (near-UV) range. Under 408 nm excitation, the CLHA:Ce3+,Tb3+ phosphors showed strong green light with emission center at 543 nm. The mechanism of energy transfer from Ce3+ to Tb3+ ions was attributed to quadruple-quadruple interaction. Impressively, the internal quantum efficiency and external quantum efficiency of the optimal CLHA:0.02Ce3+,0.5Tb3+ green phosphors were measured to be 77.1% and 55.8%, respectively. Finally, using the CLHA:0.02Ce3+,0.5Tb3+ phosphors as green-emitting color converter, a near-UV-pumped white LED device was fabricated, and under 80 mA driving current the LED device demonstrated bright warm-white light with high color rendering index (93.7), low correlated color temperature (3574 K), CIE chromaticity coordinates (0.3922, 0.3633), and high luminous efficacy (29.35 lm/W).

Multifunctional Pr3+ single doped CaLaMgTaO6: Crystal structure, thermal behavior and applications

This paper, for the first time, presents a comprehensive study of the structure, thermal stability and photoluminescence properties of CaLaMgTaO6:Pr3+ phosphors for LED applications. Pr3+ ions exhibits two clusters of dominant emissions peaked at 495 nm (3P0→3H4) and 657 nm (3P0→3F2) from double perovskite-structure CaLaMgTaO6 compounds. Meanwhile, the samples cover the emission wavelength of commercial blue light-emitting diode (LED) chips with high internal quantum efficiency (IQE) of 30.25% upon 450 nm excitation. The mechanism of thermal quenching for this phosphor was investigated and the corresponding activation energy ΔE was determined to be 0.23 eV. The fabricated Pr3+ single doped CaLaMgTaO6 together with a 450 nm blue LED chip is well-matched with the absorption band of photosynthesis, phototropism, and photomorphogenesis. Furthermore, this phosphor along with commercially available phosphors was applied to fabrication of 450 nm UV chip and YAG:Ce3+ emitted a well-distributed warm white light with high color rendering index (CRI) of 84.1 and a correlated color temperature (CCT) of 3914 K. All of the results indicate that this novel phosphor can compensate for the red light and has potential applications in plant cultivation and warm white LEDs field.

Composite Color Converters Based on Tb3Al5O12:Ce Single‐Crystalline Films and Y3Al5O12:Ce Crystal Substrates

The development of a novel composite phosphor converter based on single‐crystalline films of Tb3Al5O12:Ce garnet and Y3Al5O12:Ce single‐crystal substrate is reported. The liquid phase epitaxy growth method is chosen for the fabrication of the Tb3Al5O12:Ce/Y3Al5O12:Ce epitaxial structures with excellent photoconversion properties for application in white light‐emitting diodes (LEDs). The influence of Ce3+ concentration and thickness of Y3Al5O12:Ce substrate as well as the thickness of Tb3Al5O12:Ce films on the photoconversion properties is investigated for the construction of warm white LEDs prototypes based on the developed composite phosphor converters.