Spectroscopic investigation of novel yellow-emitting Li3Bi3Te2O12:Dy3+ phosphors with high thermal stability for w-LEDs applications

Journal of Materials Science: Materials in Electronics - A series of Li3Bi3Te2O12:xDy3+ (x?=?0.01, 0.02, 0.05, 0.10, 0.15, 0.20, and 0.30 mol) samples were successfully...     

Synthesis and photoluminescence properties of Eu2+-doped Ca2AlSi3O2N5 green phosphors

Novel Eu²⁺-doped Ca₂AlSi₃O₂N₅ phosphors with a general formula of Eu_xCa_2?xAlSi₃O₂N₅ were successfully prepared via a solid-state reaction method under a nitrogen atmosphere. The produced phosphors were effectively excited by UV–vis light in the wavelength range between 250 and 400 nm, and featured an intense green emission band which peaked at about 500 nm. The emission spectra featured a red-shift over increasing Eu²⁺ content and the temperature of heat treatment. The maximum intensity of emission was obtained for x = 0.014 and heat treatment at 1450 °C. The photoluminescence properties of the produced Ca₂AlSi₃O₂N₅:Eu²⁺ phosphors qualify them for consideration in potential use as green phosphors in UVLED-based white LED.     

Synthesis and characterization of Dy(OH)3 and Dy2O3 nanotubes

Dy(OH)3 nanotubes with high aspect ratios of up to about 50 were synthesized in the presence of poly(ethylene glycol) via a hydrothermal method. Poly(ethylene glycol), as a nonionic surfactant, plays an important role in the formation of morphologies. Subsequent thermal treatment of Dy(OH)3 nanotube precursors at 450 degrees C for 6 h led to Dy2O3 nanotubes, during which the precursor tubular morphology was maintained. Selected-area electron diffraction and high-resolution transmission electron microscopy reveal the single-crystal nature of the Dy(OH)3 and Dy2O3 nanotubes. The morphologies and crystalline structure of the as-obtained products were characterized by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction, respectively. By this method, we can obtain a mass of products.     

Synthesis and characterizations of Dy3+ doped Sr3Al2O6:Eu2+ powder phosphors through citric acid precursor

Sr₃Al₂O₆:Eu²⁺, Dy³⁺ phosphors were synthesized by the polymer precursor method. The X-ray powder diffraction patterns show that the samples have a cubic structure with a space group of Pa3. In the excitation spectrum, the phosphors show a wide absorption in the UV region from 250 to 450 nm, which corresponds to the crystal field splitting of the Eu²⁺ d-orbital. All the emission spectrum of Sr₃Al₂O₆:Eu²⁺, Dy³⁺ phosphors show the broad band emission peaked at about 518 nm, which can be ascribed to the typical 4f⁶5d¹ → 4f⁷ transitions of Eu²⁺ ions. And the best dopant concentration of Dy³⁺ ions for Sr₃Al₂O₆:2 mol%Eu²⁺, xDy³⁺ phosphors is 2 mol%. The excitation wavelengths have no influences on emission peaks, but have clear influences on emission intensities.     

Eu3+-activated Sr3LaNb3O12 red-emitting phosphors with excellent color stability for high color rendering w-LEDs

A novel red-emitting phosphor Sr₃LaNb₃O₁₂:Eu³⁺ with triclinic perovskite structure was first synthesized via the high-temperature solid-phase method. The phase purity, crystallinity, surface morphology, thermal quenching, and luminescent properties of the Sr₃LaNb₃O₁₂:xEu³⁺ (x?=?0.01–0.50 mol) phosphors were characterized. At 395-nm excitation, Sr₃LaNb₃O₁₂:Eu³⁺ phosphor emits the strongest peak at 612 nm, ascribed to the transitions of ⁵D₀→⁷F₂ by Eu³⁺ ions. The critical energy transfer distance and optimal doping concentration of Eu³⁺ ions are 11.87 Å and 0.30 mol, respectively. The relative initial intensity of Sr₃LaNb₃O₁₂:0.30Eu³⁺ just drops to 78.3% at 420 K, and the thermal quenching temperature (T_0.5) is above 480 K. By calculation, the activation energy (E_a) is 0.21 eV, and the color purity of all samples is between 99.5% and 99.8%. A white light-emitting diode (w-LED) with the chromaticity coordinates of (0.331, 0.349), a good correlated color temperature (CCT) of 5451 K, and a color rendering index (R_a) of 94 was successfully fabricated. In consequence, the feasibility of niobate red-emitting Sr₃LaNb₃O₁₂:Eu³⁺ phosphor for the white light-emitting diode was unveiled.

     

Bi3+掺杂尖晶石型LiMn2O4的合成及性能研究

采用固相反应的方法,以Li2CO3、MnO2、Bi(NO3)3·5H2O和柠檬酸为原料,合成了具有尖晶石结构的锂离子电池正极材料LiMn2-xBixO4(x=0、0.03、0.06).对材料进行了X射线衍射、扫描电镜、红外光谱、充放电等测试.实验结果表明,所合成的LiMn1.97Bi0.03O4材料具有标准的尖晶石结构,较平滑的表面外观,较高的比容量及优异的循环性能.在0.2C放电速率下,首次放电容量为117.8 mAh/g,循环30次后,容量保持率接近100%.     

Photophysical properties of Eu3+ and Tb3+-doped ZnAl2O4 phosphors obtained by combustion reaction

Europium- and terbium-doped zinc aluminate oxide nanocrystals with a spinel structure were successfully prepared by a combustion method, using urea as fuel. The samples thus obtained were characterized by X-ray diffraction, scanning electron microscopy and luminescence spectroscopy. X-ray diffraction results confirmed the formation of ZnAl₂O₄ spinel phase and a minor amount of ZnO. Our SEM results revealed agglomerates in the shape of irregular plates composed of nanoparticles with dispersed points of second phase in the surface. Powders containing Eu³⁺ and Tb³⁺ ions displayed red and green photoluminescence, respectively.     

Powder synthesis and white light-emitting properties of Eu3+ co-doped K2CaP2O7:Dy3+ phosphors with energy transfer between Dy3+ and Eu3+

A series of white-emitting K₂CaP₂O₇:Dy³⁺ and K₂CaP₂O₇:Dy³⁺, Eu³⁺ phosphors were synthesized via a solid-state method, and Eu³⁺ was co-doped in K₂CaP₂O₇:Dy³⁺ to improve its white light performance. The influences of preparation temperature and Dy³⁺/Eu³⁺ concentration on the crystal structure and photoluminescence characteristics were investigated. XRD results indicate that K₂CaP₂O₇:Dy³⁺ samples prepared above 700 °C matches the standard K₂CaP₂O₇ phase. Under excitation of 349 nm, K₂CaP₂O₇:Dy³⁺ phosphor exhibited characteristic emission peaks at 487 nm (blue) and 579 nm (yellow), and white emission was realized through combining these blue and yellow emissions. After co-doping Eu³⁺ ions, the co-luminescence of Dy³⁺/Eu³⁺ with energy transfer between Dy³⁺and Eu³⁺ were demonstrated. The chromaticity of white light was controlled by changing the ratio of Dy³⁺/Eu³⁺ concentrations, which lead to a warm white light. Therefore, the results indicate that K₂CaP₂O₇:Dy³⁺, Eu³⁺ powders have a potential application in w-LEDs as single-component white-emitting phosphor.     

Combustion synthesis and luminescence properties of yellow-emitting phosphors Ca2BO3Cl:Eu2+

Yellow-emitting phosphor Ca₂BO₃Cl:Eu²⁺ was synthesized by a solution-combustion method. The phase structure and microstructure were determined by the X-ray diffraction (XRD) and scanning electron microscope (SEM) analysis, respectively. The as-prepared Ca₂BO₃Cl:Eu²⁺ phosphor absorbed near ultraviolet and blue light of 320–500 nm, and showed an intense yellow emission band centered at 569 nm with the CIE coordinate of (0.453, 0.526). The lifetime of Eu²⁺ ions in Ca₂BO₃Cl:Eu²⁺ phosphor was measured, furthermore the temperature dependent luminescence property and mechanism were studied, which also testified that the present phosphor had a promising potential for white light-emitting diodes.     

Analytical transmission electron microscopy of La2O3-doped Y2O3

Analytical electron microscopy has been used to study the precipitation reactions in sintered samples of 9 mol% La₂O₃-Y₂O₃ samples upquenched from the single phase cubic region into the cubic and hexagonal phase field. Samples annealed just inside the two-phase cubic-cubic and hexagonal solvus exhibited predominantly grain boundary precipitation. Small La₂O₃ rich second phases formed within the first ten minutes and developed into strained, facetted precipitates after 300 min. Intergranular and intragranular precipitation occurred in samples annealed further into the two-phase field. Strained, lathlike La₂O₃-rich monoclinic precipitates, exhibiting a preferrred orientation in the matrix, appeared as the dominant morphology for long times at temperature. Chemical microanalyses of the strained structures obtained in samples annealed for 300 min revealed La₂O₃ matrix concentrations in agreement with phase diagram predictions. However, the La₂O₃ concentrations in the second-phase precipitates were found to be far in excess of the cubic and hexagonal-hexagonal solvus. This discrepancy is believed to arise from a re-equilibration of the second phase in the cubic and monoclinic phase field during quenching.     

Synthesis and luminescence of Dy3+-activated NaSrPO4 phosphors for novel white light generation

The Dy³⁺-doped NaSrPO₄ phosphor powders have been synthesized by solid state reaction. All samples were verified to be in a pure NaSrPO₄ phase by X-ray diffraction analysis for all the Dy³⁺ doping concentrations. The room temperature excitation spectra of NaSrPO₄:Dy³⁺ phosphors illustrated that they could easily be excited by UV–Visible light corresponding f ? f transitions of Dy³⁺. The photoluminescence spectra exhibit two main bands centered at 481 nm (blue) and 573 nm (yellow), which originate from the ⁴F_9/2 → ⁶H_15/2 and ⁴F_9/2 → ⁶H_13/2 transitions of Dy³⁺, respectively. The two bands combined to form a white light with the chromaticity coordinates varying with the concentrations of Dy³⁺. The chromaticity coordinates were measured and mapped in the Commission International de L’Ecllairage 1931 diagram, indicating that they distributed around (0.30, 0.34) of the colorless point D65. The dependence of luminescence intensity onto Dy³⁺ concentration was investigated and the concentration quenching mechanism for NaSrPO₄:Dy³⁺ was discussed.     

The development of Ce3+-activated (Gd,Lu)3Al5O12 garnet solid solutions as efficient yellow-emitting phosphors

Abstract

Ce³⁺-activated Gd₃Al₅O₁₂ garnet, effectively stabilized by Lu³⁺ doping, has been developed for new yellow-emitting phosphors. The powder processing of [(Gd_1?xLu_x)_1?yCe_y]₃Al₅O₁₂ solid solutions was achieved through precursor synthesis via carbonate precipitation, followed by annealing. The resultant (Gd,Lu)AG:Ce³⁺ phosphor particles exhibit typical yellow emission at ～570 nm (5d–4f transition of Ce³⁺) upon blue-light excitation at ～457 nm (the ²F_5/2–5d transition of Ce³⁺). The quenching concentration of Ce³⁺ was determined to be ～1.0 at% (y = 0.01) and the quenching mechanism was suggested to be driven by exchange interactions. The best luminescent [(Gd_0.9Lu_0.1)_0.99Ce_0.01]AG phosphor is comparative to the well-known YAG:Ce³⁺ in emission intensity but has a substantially red-shifted emission band that is desired for warm-white lighting. The effects of processing temperature (1000–1500 °C) on the spectroscopic properties of the phosphors, especially those of Lu³⁺/Ce³⁺, were thoroughly investigated and discussed from the centroid position and crystal field splitting of the Ce³⁺ 5d energy levels.     

Synthesis and luminescent properties of Eu3+ and Dy3+ doped BiPO4 phosphors for near UV-based white LEDs

The phosphors BiPO₄:Eu³⁺ co-doped with Dy³⁺ were synthesized by the conventional solid-state reaction method. XRD and scanning electron microscopy results showed that the crystalline phase of the samples BiPO₄:Eu³⁺ transforms from high-temperature monoclinic phase to low-temperature monoclinic phase with the increase of Dy³⁺ concentration. The photoluminescence properties of the samples showed that the colors shifting from red–orange area to blue–green area are close to those of ideal white light by readjusting the doping concentration ratio of Eu³⁺ and Dy³⁺. The Eu³⁺and Dy³⁺ doped BiPO₄ phosphors may be potential applications in white light near-UV light-emitting diodes.     

Investigation on photoluminescence properties and defect chemistry of GdAlO3:Dy3+ Ba2+ phosphors

GdAlO₃:Dy³⁺ Ba²⁺ phosphors are synthesized by citrate-based sol-gel method. Photoluminescence and positron annihilation studies are used to investigate the emission and defect chemistry of the phosphors respectively. The strong yellow (Dy³⁺) emission properties of phosphors are discussed for various concentrations of Dy³⁺ ions. Upon the addition of Ba²⁺ ion, an enhancement in emission intensity is observed due to the lattice distortions around Dy³⁺ ion. The positron studies indicate the presence of defects at crystallite boundaries, vacancy clusters and large voids in the materials. The influence of Ba²⁺ ion on the photoluminescence and lattice distortion around Dy³⁺ is also explored.