Phosphor For White Light-emitting Diodes Research Articles

Atomic-level investigation of structure and formation process of Y3Al5O12 with super-high content of Ce emitting anomalous orange-red emissions

Ce-doped yttrium aluminum garnet (YAG:Ce, Y3Al5O12:Ce) is the most commonly used yellow phosphor in white light-emitting diodes. Recently, we found that (Y1–xCex)3Al5O12:Ce with a super-high content of Ce (x = 0.11–0.21) can be prepared by a polymerized complex method and exhibits anomalous orange–red emission. To understand the nature of this anomalous behavior from the atomic level, we applied high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and scanning transmission electron microscopy–energy dispersive X-ray spectroscopy (STEM-EDS), a state-of-the-art technique that enables analysis of the atomic-level elemental distributions of Al, Y, and Ce. STEM-EDS images on the atomic level were successfully obtained for YAG:Ce. It was found that Ce in Y site has spatially uneven for few nanometers. Ce–K edge extended X-ray absorption fine structure (EXAFS) analysis was also conducted, which revealed a high level of asymmetry around Ce. By combining the STEM-EDS and EXAFS results, a dynamic model for the red emission was proposed. STEM-EDS also revealed that CeO2 nanocrystals were firstly formed with low-temperature annealing and that the reaction of Y with the CeO2 nanocrystals subsequently yielded YAG:Ce, unlike in the conventional one-step high-temperature synthesis.

Thermally-stable and color-tunable novel single phase phosphor Ca2GaTaO6:Dy3+, Sm3+ for indoor lighting applications

This study successfully synthesized novel phosphors Ca2GaTaO6:xDy3+ (CGTO:xDy3+) and Ca2GaTaO6:0.06Dy3+, ySm3+ (CGTO:0.06Dy3+, ySm3+) using the high temperature solid-phase reaction preparation. The microstructure, optical properties, and energy transfer mechanism of the phosphors were studied through X-ray diffraction (XRD), scanning electron microscope (SEM), photoluminescence (PL) spectra and fluorescence lifetimes. XRD and corresponding refinement results indicate that Dy3+ and Sm3+ ions were effectively doped into the Ca2GaTaO6 (CGTO) lattice. The SEM graphs show that the elements in CGTO:0.06Dy3+, 0.5Sm3+ phosphors are uniformly distributed. PL spectra analysis show the CGTO:xDy3+ phosphors display two strong emission peaks located at 482 nm for blue emission and 575 nm for yellow emission when excited with 350 nm light. Under uniform conditions, when excited with 365 nm of light, the CGTO:0.06Dy3+, ySm3+ phosphors emit light that can be tuned with adjustable color coordinates and correlated color temperature (CCT) by incorporating varying proportions of Sm3+ ions. This tunability is achieved through the effective energy migration from Dy3+ to Sm3+ ions within the phosphor material. Furthermore, the emission spectra and weaken lifetimes of the CGTO:0.06Dy3+, ySm3+ confirm the energy transport between Dy3+ and Sm3+, and the energy transfer efficiency reached to 76 %. At 423 K, the luminescence intensity of CGTO:0.06Dy3+, 0.05Sm3+ phosphor retains 87 % of the intensity observed at 298 K, signifying its excellent thermal durability. Finally, the electroluminescent performance of the CGTO:0.06Dy3+ and CGTO:0.06Dy3+, 0.05Sm3+ phosphors packaged on 365 nm light-emitting diode (LED) chips respectively were studied to investigate the capability applications of the phosphors in white light-emitting diodes (WLEDs) field. The CCT of the packaged LEDs decline from 3396 to 2825 K, indicating CGTO:0.06Dy3+, 0.05Sm3+ phosphor shifts to warmer white light. At a voltage input of 3.4 V and a current of 600 mA, the thermal sensing shows that the WLEDs maintain aptitude for 90 min, showing that the packaged WLEDs can function consistently under elevated temperatures. These studies indicated the phosphors have potential applications in indoor lighting.

Microstructure, optical, and electrical characteristics of NaBaBi2(PO4)3: Sm3+ orange-red phosphor for WLEDs

White light-emitting diodes (WLEDs) are widely used as lighting devices in daily life. However, due to the scarcity of orange-red components, they lack warm white light. Therefore, there is an urgent need for orange-red phosphors to improve the lighting quality and generate more saturated and warm white light. In this regard, NaBaBi2(PO4)3: xSm3+ orange-red phosphors were synthesized using the solid-state method. A systematic study was conducted on the microstructure, optical, and electrical properties of NaBaBi2(PO4)3: xSm3+ phosphors through various characterizations such as X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, diffuse reflectance spectroscopy, photoluminescence spectroscopy, fluorescence decay curves, and electrochemical impedance spectroscopy. The diffuse reflectance spectrum indicates that with the increase of Sm3+ doping concentration, the optical bandgap decreases. Remarkably, the NaBaBi2(PO4)3: 0.05Sm3+ phosphor has good thermal stability, and its retention rate is 84.42% at a high temperature of 428 K. Furthermore, the packaged LED manifested desirable characteristics, such as a low correlated color temperature (CCT ∼ 4280 K) and a high color rendering index (CRI ∼ 82), as evidenced by rigorous testing. These results indicate that the NaBaBi2(PO4)3: Sm3+ phosphors have a significant potential for utilization in the LED lighting industry.

Crystal structure, Bi3+ yellow luminescence, and high quantum efficiency of Ba3SbAl3Ge2O14:Bi3+ phosphor for white light-emitting diodes

Bi3+ ions occupy Ba site to form one Bi3+ luminescent center, which is consistent with the trigonal structure of BSAG. This phosphor has a high quantum efficiency of 95.3% and can be used in WLEDs.

Ultra-broadband emission up to 181 nm of VO4-activated yellow phosphor for white light-emitting diodes with high color rendering index

Exploring broadband yellow phosphors capable of covering the cyan to red region is an effective approach to achieve high-performance phosphor-converted white light-emitting diodes (pc-WLEDs). Herein, we synthesized a series of VO4-activated ultra-broadband KSrP1−xVxO4 (0.1 ≤ x ≤ 1) yellow phosphors via high temperature solid-state reaction. Successive substitution of P5+ with V5+ causes a slight expansion of the lattice constant and induces several highly localized energy-levels within the forbidden band. Density functional theory calculations confirm that these newly appeared sharp-line energy-levels are attributed to the constructed VO4 anionic groups. With the optimized V5+ content, the KSrP0.7V0.3O4 phosphor exhibits an ultra-broadband yellow emission centered at 537 nm under 355 nm excitation. Impressively, its full width at half maximum is up to 181 nm, exceeding that of most reported counterparts. At 105 °C, the KSrP0.7V0.3O4 sample experiences an emission loss of 53%. A WLED device is fabricated by using phosphor blend of KSrP0.7V0.3O4 yellow phosphor and the commercial BaMgAl10O17: Eu2+ blue phosphor and a 355 nm NUV LED chip, demonstrating bright white emission with high color rendering index (CRI) of 90 and suitable correlated color temperature of 5953 K. These findings indicate that this phosphor has great potential for achieving high CRI WLEDs.

Synthesis and warm white emission performance of single-component Ca7Mg2(PO4)6:Dy3+, Eu3+ phosphor for white light-emitting diodes

A single-component Ca7Mg2(PO4)6:Dy3+, Eu3+ white-emitting phosphor was synthesized by a sol-gel approach. The effects of the amounts of Dy3+ ions and Eu3+ ions on the luminescence characteristics and crystal structure of Ca7Mg2(PO4)6:Dy3+, Eu3+ were systematically investigated. The Ca7Mg2(PO4)6:Dy3+, Eu3+ phosphors had a Ca7Mg2(PO4)6 structure with an R3c (161) space group. The Ca7Mg2(PO4)6:Dy3+ phosphor showed emission peaks at both 484 nm (blue) and 576 nm (yellow), which led to the realization of white light. Furthermore, after codoping Eu3+ ions into the structure, a red emission peak (∼617 nm) appeared in the spectrum as a supplementary red component. A warm white light with a low correlated colour temperature (CCT) is obtained from Dy3+/Eu3+-codoped Ca7Mg2(PO4)6. The luminescence intensity at 483 K still reaches more than 73 % of that at 303 K. The packaged LEDs display a bright warm white light with CCT value and colour rendering index (CRI) of 3878 K and 86.7, respectively, which is comfortable for the human eye. With excellent luminescence performances, the white-emitting Ca7Mg2(PO4)6:Dy3+, Eu3+ phosphor had a significant application potential in the w-LED field.

New green garnet-type phosphor LuMgAl5SiO12:Ce3+ for filling cyan gap to achieve full-spectrum and high colour-rendering-index white light-emitting diodes

Phosphors with simple preparation, high luminous efficiency and excellent thermal stability are highly desirable for commercial white light-emitting diodes (W-LED). In the paper, a new garnet-type green phosphor LuMgAl5SiO12:Ce3+ (LMASO:Ce3+) has been successfully prepared by a high-temperature solid-state reaction. The crystal structure and photoluminescence properties were investigated in detail. X-ray diffraction and the Rietveld refinement demonstrated the crystal structure of LMASO belongs to cubic systems with an Ia 3¯ d (230) space group. The unit cell parameters of LMASO:0.08Ce3+ phosphor were found to be a = 11.90418 Å and V = 1686.935 Å3. LMASO:Ce3+ phosphors have two excitation bands with peaks at 340 and 436 nm, attributed to the 4f → 5d transition of Ce3+ ions. Under excitation at 436 nm, LMASO:0.08Ce3+ phosphor exhibits a broad and asymmetric emission band in the 450–700 nm range. Notably, a W-LED device was created by combining a 455 nm blue LED chip with the obtained green sample and the commercially available red CaAlSiN3:Eu3+ phosphor. The device emitted a bright warm white light with a low correlated color temperature of 3584 K and a high color rendering index of 96.0 at a drive current of 40 mA. The article indicates that LMASO:Ce3+ samples can serve as a potential green phosphor for W-LEDs, and offers a new strategy for designing efficient phosphors.

A highly thermal-stable red-emitting tantalate phosphor for WLED and multiple-mode optical temperature sensor dual-applications

Recently, more and more attention has been concentrated on luminescence materials activated with rare-earth ions for white light-emitting diodes (WLEDs) or optical thermometers. However, due to their opposite requirements for thermal response, it is hard to realize the above dual applications in the same material. Herein, a red-emitting tantalate phosphor, Gd3TaO7:Eu3+, was designed and prepared to solve the problem. The emission of Eu3+ in the phosphor was surprisingly observed to be different from that in most of the reported red phosphors activated with Eu3+, that is, the emissions coming from the f - f transitions of Eu3+ exhibit severe splitting, and the intensities of several strong transitions are not very different. According to the structural and spectral analyses, the reasons may be the highly covalent and polarized lattice environments of Eu3+ in this material. When excited with 393 nm, the temperature-dependent photoluminescence (TDPL) of Gd3TaO7:Eu3+ presents a normal thermal quenching and the integrated intensity at 500 K keeps 90.8 % compared to that at 300 K. Whereas the TDPL presents an edge abnormal thermal quenching phenomenon upon the excitation of 330 nm. Taking advantage of the special TDPL characteristics, a WLED device and a multiple-mode optical thermometer are successfully realized in this material. The former has excellent performances with high Ra of 88.8 and low CCT of 3882 K, and the latter includes one type of excitation intensity ratio and two types of fluorescence intensity ratio with the maximal relative temperature sensitivities of 0.92 % K−1, 0.97 % K−1 and 0.92 % K−1, respectively. The results reveal that Gd3TaO7:Eu3+ phosphor has a great prospect in WLED and multiple-mode optical temperature sensor dual-applications, and this work may provide a new and effective strategy for developing multifunctional optical materials.

Anomalous 5D0→7F4 Transition of Eu3+‐Doped BaLaGaO4 Phosphors for WLEDs and Plant Growth Applications

AbstractEuropium (Eu3+) doped phosphors typically exhibit orange or red emission and are used in lighting and display applications, originating from the 5D0→7F1 and 5D0→7F2 transitions of Eu3+. However, BaLaGaO4: xEu3+ deep‐red phosphor, when excited by near‐ultraviolet light, is mainly 5D0→7F4 transition (703 nm). Meantime, the BaLaGaO4: 0.30Eu3+ exhibits a high I423K/I298K value of 71% and a high quantum yield of 82.54%. Furthermore, the prepared samples are mixed with commercial blue and green phosphors in a certain proportion to make white light‐emitting diodes (WLEDs). The color coordinate of the fabricated WLEDs is (0.3208, 0.3436), with a color rendering index of 91.9 and an R9 value of 73. Based on the unique spectral characteristics of this compound, a prototype device of a deep‐red LED with phosphor conversion is developed, which exhibits color coordinates (0.6294, 0.3581) and a color purity of 96.4%. The conducted germination experiments with plant seeds have provided compelling evidence regarding the considerable positive effects of the deep‐red LEDs on plant growth. These findings further emphasize the highly promising potential application of BaLaGaO4: Eu3+ deep‐red phosphor in WLEDs and plant growth lighting.

Efficient bright green phosphor for white light-emitting diode using in backlight application

The (Ba,Ca)ScO2F:Bi3+,K+ phosphor with narrow emission band and green emission color peaking at 510 nm is demonstrated in the study. This phosphor is prepared using a solid-state reaction at high temperatures. Based on characterizing data, the increasing concentration of Ca2+ induces the shrinkage of the unit cell and the narrower spacing, leading to the increase in the photoluminescence of the phosphor. This also cause a red shift in the emitting range from 504 nm to 510 nm. The phosphor shows good absorption peaking at 415 nm, matching the excitation wavelength of the used nearultraviolet (UV) light emitting diode (LED) chip. When being applied in a white light‐emitting diodes (WLED) with 4,000 K, the phosphor could increase the luminous flux as its doping concentration increase. Besides, the WLED doping (Ba, Ca) ScO2F: Bi3+, K+ shows emission regions in blue, green, and red wavelength bands. The data from the study indicates that the phosphor is potential for developing the white-LED for backlight purposes.

Broadband emission characteristics and WLED application of self-activated YMZn3AlO7 (M=Ca, Sr, Ba) phosphors

In this study, a non-activated ion-doped full-spectrum emission phosphor for white light-emitting diode (WLED) lighting is proposed using oxygen defect engineering. The YMZn3AlO7 (M = Ca, Sr, Ba) phosphors with "114″ structure were prepared via a high-temperature solid-state reaction. Under excitation with 373 nm ultraviolet (UV) light, YSrZn3AlO7 in YMZn3AlO7 (M = Ca, Sr, Ba) exhibited the highest emission intensity and formed a wide yellow emission band centred at 563 nm. The full width at half maximum of the YSrZn3AlO7 phosphor was 172.6 nm. A theoretical model based on the designed oxygen vacancies was proposed to determine the self-activated luminescence mechanism. Density functional theory calculations revealed that oxygen vacancies lead to the generation of new energy levels. Electron paramagnetic resonance experiments further confirmed that the luminescence originated from oxygen vacancies. Eventually, a warm WLED device ((x, y) = (0.4057, 0.4359)) with a correlated color temperature of 3814 K and a relative color rendering index of 83 was successfully prepared using the YSrZn3AlO7 phosphor and a 365 nm UV LED chip. These results suggest that YSrZn3AlO7 is a promising WLED phosphor and provide new insights into the application of self-activated phosphors in WLED.

Structural, optical, and luminescence properties of Dy3+ -activated potassium calcium silicate phosphor for white light-emitting diodes.

A dysprosium (Dy3+ )-activated potassium calcium silicate (K4 CaSi3 O9 ) phosphor was prepared using a solid-state synthesis route. The phosphor had a cubic structure with the space group Pa as confirmed using X-ray diffraction (XRD) measurements. Details of surface morphology and elemental composition of the as-synthesized undoped KCS phosphor was obtained using scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) spectroscopy. The chemical structure as well as the vibrational modes present in the as-prepared KCS phosphor was analyzed using Fourier transform infrared (FT-IR)spectroscopy. Diffuse reflectance spectra (DRS) were used to determine the optical bandgap of the phosphors and were found to be in the optical range 3.52-3.71 eV. Photoluminescence (PL) spectra showed intense yellow emission corresponding to the 4 F9/2 →6 H13/2 transition under 350 nm excitation. Commission International de l'Eclairage colour chromaticity coordinates were evaluated using the PL spectral data lie within the white region. Dexter theory and the Inokuti-Hirayama (I-H) model were applied to study the nature of the energy transfer mechanism in the as-prepared phosphors. The relatively high activation energy of the phosphors was evaluated using temperature-dependent PL (TDPL) data and confirmed the high thermal stability of the titled phosphor. The abovementioned results indicated that the as-prepared KCS:Dy3+ phosphor was a promising candidate for n-UV-based white light-emitting diodes.

A yellow-green-emitting graphitic-C3N4 derivative consisting of 1,4-phenylene-inserted heptazine units: Preparation and application as a metal-free phosphor for white LEDs

To develop non-rare-earth or metal-free phosphors for white light-emitting diodes (WLEDs) are very significant and forward-looking. Here, a yellow-green-emitting g-C3N4 derivative (p-Ph-g-C3N4) consisting of 1,4-phenylene-inserted heptazine units was successfully prepared by 6,6'-(1,4-phenylene)bis(1,3,5-triazine-2,4-diamine) via thermal polymerization. Its emission is mainly located at 450–700 nm with the maximum wavelength (λem,max) of 536 nm, its quantum yield (QY) is 15.7% (λex = 430 nm) which is much higher than that of bulk g-C3N4 (ca. 5%). Under the excitation of 430 nm blue-emitting GaN-based chips (ca. 4.0 lm·W−1), p-Ph-g-C3N4 together with non-rare-earth red-emitting K2SiF6:Mn4+ as phosphors, a series of cold, neutral, and warm WLEDs with good performances were fabricated. As for the best one, its color rendering index (CRI) is 84.3, correlate color temperature (CCT) is 5702 K, luminous efficiency (LE) is 5.40 lm·W−1, moreover, its CIE value (0.30, 0.34) is very close to (0.33, 0.33) of pure white light. The research results indicate p-Ph-g-C3N4 can be used as an efficient metal-free quasi-green phosphor for WLEDs.

Key role of Nb5+ in achieving water-resistant red emission in K2Ta1-xNbxF7:Mn4+ phosphors

Mn4+-activated fluoride is one of the most important red phosphors for white light-emitting diodes (WLEDs) with high color rendering index (CRI). Due to a lack of water resistance, their potential applications are limited. Although surface coating strategies improve the waterproof stability of fluoride red phosphors, they have downsides. It was found that Nb5+ plays an important role in improving the water resistance of Mn4+-activated oxyfluorides by preventing the hydrolysis of [MnF6]2-. In this work, the influence of Nb5+ on the waterproof stability of Mn4+-activated fluorides was explored. A set of synthesized K2Ta1-xNbxF7:Mn4+ phosphors exhibit tunable and superior water resistance. The photoluminescence (PL) intensity of the representative sample K2Ta0.6Nb0.4F7:5%Mn4+ remains nearly 100% of its initial value even after being immersed in water for 60 min, which is significantly higher than the commercial K2SiF6:Mn4+ red phosphor (8.7%). Our findings open up new possibilities for the development of waterproof fluoride red phosphors.

Effect of A3+ (A = Y, Bi) codoping on the enhancement of photoluminescence performance of Li5La3Nb2O12:Eu3+ red-emitting phosphor for white light-emitting diodes

The Li5La3Nb2O12:Eu3+ red-emitting phosphors with Y3+/Bi3+ codoped are prepared via sol-combustion for improving the luminescence performance. All samples with single Li5La3Nb2O12 structure are obtained, without the impurity phases of Y3+ and Bi3+. After codoping Y3+ and Bi3+, the luminescence intensity at 609 nm increases 1.77- and 1.61-fold compared to that of Li5La3Nb2O12:Eu3+, respectively. The actual w-LEDs are realized through combining the as-prepared Li5La3Nb2O12:Eu3+, A3+ red phosphor and commercial blue/green phosphors, which exhibiting the soft and bright white light. Furthermore, the as-prepared red-emitting phosphor is also packaged in commercial w-LEDs to improve the chromatic parameters of white light. Therefore, all the results demonstrate that the Li5La3Nb2O12:Eu3+, A3+ red phosphor with excellent performance has an application value in warm w-LEDs field.

Photoluminescence in Cerium-Doped Fluoride Borate Crystals

Antizeolite fluoride borates LiBa12(BO3)7F4 (LBBF) doped by Ce3+ ions demonstrate photoluminescence (PL) and hold promise for use as phosphors in white light-emitting diodes. In this study, we present the results of modeling the electronic and optical properties of Ce-containing LBBF structures where doping atoms are located at different sites of the host lattice. We also consider the presence of F-centers, which exhibit trap states located within the band gap. We further investigate the nonadiabatic excited state electronic dynamics to elucidate electron-relaxation pathways. The nonadiabatic couplings (NACs) calculations provide transition probabilities facilitated by the nuclear movement. The relaxation rates of electrons and holes are calculated using Redfield’s theory of the formalism of the reduced density matrix (RDM). The PL spectra are calculated using molecular dynamics (MD) sampling and time-integrated methods along the excited state trajectory based on NACs. Mechanisms of PL in LBBF:Ce3+ crystals are interpreted using both computational and experimental observations. This work illustrates the dependence of transition energies, intensities, and relaxation rates of Ce-containing LBBF crystals on a selection of doping sites. In addition to analysis of emission band contributed by cerium, this work allows to identify and reproduce spectral lines hypothetically corresponding to the interband and intraband transitions in F-centers of borate crystals, available in the absence of a metal center.

Enhancement on Tb3+ luminescence in CaScBO4-based ceramic phosphors by Ce3+-induced resonance energy transfer and the generation of white light emission collaborated with Mn2+

A series of Tb3+-doped, Ce3+,Tb3+-co-doped and Ce3+,Tb3+,Mn2+-tri-doped CaScBO4 (CSB) ceramic phosphors were prepared by solid-state reaction. X-ray diffraction (XRD) was taken to confirm the phase purity of all as-prepared phosphors powder. Steady-state and transient-state fluorescence spectra were applied to evaluate the luminescence properties of the phosphors. The results indicated that significant enhancement on Tb3+ luminescence was successfully realized by the Ce3+-induced resonance energy transfer and confirmed that the energy transfer from Ce3+ to Tb3+ was governed by an electronic dipole-dipole interaction. Compared to the CSB:Tb3+ phosphors whose optimal excitation located at 378 nm, the occurrence of Ce3+-Tb3+ energy transfer not only allowed the optimal excitation to peak at around 390 nm but also gifted the CSB:Ce3+,Tb3+ phosphors color tunability from blue, cyan to green. Then, two different designs of white light by the introduction of Mn2+ luminescence were performed. One was the combination of CSB:Ce3+,Tb3+ and CSB:Ce3+,Mn2+ phosphors, based on the co-excitation of the above two phosphors at the same wavelength. Another was the direct use of the tri-doped CSB:Ce3+,Tb3+,Mn2+ phosphors. Both designs succeeded in the generation of white light emission. The performance of these two designs in real devices were also studied. The direct use of the tri-doped CSB:Ce3+,Tb3+,Mn2+ phosphor in white light-emitting diode (WLED) device can produce white light with a color rendering index (CRI) up to 85.3 while the use of the CSB:Ce3+,Tb3+ and CSB:Ce3+,Mn2+ phosphors combination can just produce a value of 76.6 in CRI.

Anionic Regulation toward Bi3+ Selective Occupation for Full-Spectrum White Light Emission.

An activator's selective occupation of a host is of great significance for designing high-quality white light-emitting diode phosphors, while achieving a full-spectrum single-phase white light emission phosphor is challenging. In this study, a boron phosphate solid-solution Na2Y2(BO3)2-x(PO4)xO:0.005 Bi3+ (NYB2-xPxO:0.005 Bi3+) white phosphor was designed by selectively occupying Bi3+ activators in the mixed anionic groups. The substitutes of the anionic unit (BO3)3- by the (PO4)3- unit are supposed to force part of the Bi3+ ion to enter the Na lattice site, which produces an intense orange-red emission peaked at 590 nm. In parallel, spectral tuning from blue to white light and an internal quantum efficiency of 56.42% was obtained, and the thermal stabile luminescence intensity remains at 94.2% of the initial intensity after four heating-cooling cycles from 30 to 210 °C (luminescent intensity is 83.6% of room temperature (RT) at 150 °C, with excellent thermal stability and recovery performance). Finally, an excellent color rendering index (Ra = 90.8 and R9 = 85) was demonstrated for white light-emitting diode devices using only an NYB1.5P0.5O:0.005 Bi3+ phosphor and a near-ultraviolet (n-UV) 365 nm LED chip. This work delves into the different selective occupancy of Bi3+ ions and explores a new avenue for the design of phosphors for full-spectrum white light emission.

One-Step Synthesis of White-Light-Emitting Carbon Dots for White LEDs with a High Color Rendering Index of 97.

White-light-emitting carbon dots (WCDs) show innate advantages as phosphors in white light-emitting diodes (WLEDs). For WLEDs, the color rendering index (CRI) is the most important metric to evaluate its performance. Herein, WCDs are prepared by a facile one-step solvothermal reaction of trimellitic acid and o-phenylenediamine. It consists of four CDs identified by column chromatography as blue, green, yellow, red, and thus white light is a superposition of these four types of light. The mixture of the four CDs undergoes Förster resonance energy transfer to induce the generation of white light. The photoluminescence of WCDs originates from the synergistic effect of carbon core and surface states. Thereinto, the carbon core states dominate in RCDs, and the increase of amide contents and degree of conjugation promote the redshift of the emission spectra, which is further confirmed by theoretical calculations. In addition, a high CRI of 97 is achieved when the WCDs are used as phosphors to fabricate WLEDs, which is almost the highest value up to now. The multicolor LEDs can also be fabricated by using the four multicolor CDs as phosphors, respectively. This work provides a novel approach to explore the rapid preparation of low-cost, high-performance WCDs and CDs-based WLEDs.

Intensity enhancement of photoluminescence in Tb3+ /Eu3+ co-doped Ca14 Zn6 Al10 O35 phosphor for WLEDs.

This article focuses on the effect of monovalent cation doping on the optical properties of rare earth (RE = Eu3+ , Tb3+ ) co-doped Ca14 Zn6 Al10 O35 which has been synthesized by a low temperature combustion method. Crystalline phase of the Ca14 Zn6 Al10 O35 phosphor was examined and confirmed by X-ray diffraction measurement. Under near-ultraviolet light excitation Eu3+ -doped Ca14 Zn6 Al10 O35 phosphor exhibit characterization of Eu3+ emission bands that are located at a maximum wavelength (λmax ) of approximately 470 nm and other peaks centred at 593 nm and 615 nm, respectively. With Tb3+ -doped Ca14 Zn6 Al10 O35 phosphor showing a green emission band centred at 544 nm under near-ultraviolet range. Furthermore, we studied the energy transfer process in Eu3+ /Tb3+ pair and enhancement in photoluminescence (PL) intensity with doping different charge compensation. Here we obtained the optimum PL emission intensity of the phosphor in broad and intense visible spectral range which may be significant for the fabrication of white light emitting diodes (WLEDs).