| Under the urgent situation of energy shortage and environmental pollution problems globally, the green energy-efficient lighting technology has been paid more and more attention. White light emitting diodes (W-LEDs) offer many advantages such as lower voltage, environmental friendship, higher efficiency, good stability, longer operation lifetime compared with conventional incandescent lamp and fluorescent lamp, which is considered to be the fourth generation solid-state light source. The W-LEDs by using an ultraviolet (UV) LED to stimulate singe-phased white-emitting emitting phosphors have the characters of stable emitting color, high color rendering index and low cost. So the research of single-phased white-emitting phosphors has been attracted more attention and it seems significant to develop some more novel efficient and stable single-phased white-emitting phosphor.In this paper, two kinds of new singe-phased vanadate phosphors Ba3-xMgLiV3O12:xEu3+and Sr2-xV2O7:xEu3+was prepared by high temperature solid-state process. The crystal structure, morphology and photoluminescence properties of samples under different preparation technology were characterized by powder X-ray diffraction (XRD) analysis, Scanning Electron Microscope (SEM) and F-2500spectrofluorometer. We have got the important conclusions below. The vanadate phosphors Ba3-xMgLiV3O12:xEu3+prepared by solid-state reaction method exhibited a broadband excitation covering from260nm to395nm, and the main peak was around343nm. The emission spectrum contained two parts:a typical broadband covering from400nm to600nm which main peaks in500nm and emission spectrum at613nm corresponding to the forced electric dipole5D0-7F2optical transition dominates the Eu3+. There was great energy migration from the vanadate host lattice to the Eu3+activator and the emission intensity was influenced by the Eu3+concentration. The phosphors with different color composition could be obtained via changing the doped concentration of Eu ions and white light of Ba3-xLiMgV3O12:xEu3+(x=0.02,0.05,0.10) was obtained when the doping concentration (x) was5.0mol%and the CIE chromaticity coordinates of Ba2.95LiMgV3O12:0.05Eu3+was x=0.312and y=0.321which was very close to that of the standard white light point of (0.333,0.333). Several W-LEDs which were fabricated through the combination the-365nm UV chip with synthesized phosphor have lower color temperature (6600K) and higher color rendering index (92) compared with commercial solid state lighting.Another kind of vanadate phosphors Sr2-xV2O7:xEu3+was prepared by modified solid-state reaction method. The effects of different compound (Li2CO3, Na2CO3, K2CO3) on the luminescence behavior of prepared phosphors have been investigated and we concluded that the additive play an important role as charge compensation and fluxing agent during sample preparation. The Sr2-xV2O7:xEu3+phosphor has similar photoluminescence property in comparison to Ba3-xMgLiV3O12:xEu3+and strong energy transfer has been observed between Eu3+and VO43+White light emission obtained by combining the yellow green light from the VO4host with red light emmiting from the Eu3+dopant. When the Eu3+doping concentration (x) of Sr2-xV2O7:xEu3+was fixed as x=0.10, the W-LEDs which used the sample phosphors emmits warm white light (6126K) and appears higher color rendering index (91) and the color coordinates of its was (0.320,0.325), which was close to standard white point (WP).The solid-solid reaction method has been used widespreadly to synthesize inorganic materials because of its facile operation. In this paper, vanadate phosphors with good photoluminescence property have been prepared by above method, which have lower color temperature and higher color rendering index considering being a promising UV excited single-phased white-emitting phosphor for W-LEDs. The research methods in this paper have also accumulated experience for synthesizing some other luminescent material. |
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