Wet Chemical Preparation And Propertics Of Scverai Phosphors For White LEDs

LEDs, which are of green, energy-conservation, long-lifetime, are candidates for lighting and display devices. They will replace traditional light source in the future, on which has become consensus in the academic and industry circles of the world. With the development and application of semiconductor lighting technology, researches on white LEDs have received increasing interests from the scientific research groups. Phosphors are one of the key materials for white LEDs, therefore, the research on special fluorescent materials for white LED is undoubtedly of great practical significance.In this paper, several wet-chemical routes such as the polymer network gel method, modified sol-gel route and starch combustion method have been attempted to prepare a series of Ce3+doped yttrium aluminum garnet, alkali metal metavanadate and rare earth ions doped Sr2CeO4luminescence materials, respectively. And then their properties were also characterized. Further, luminescence mechanisms were discussed by researching the photoluminescence behavior systematically. (1) Gd3+or Pr3+doped YAG:Ce phosphors were prepared for GaN blue-LED. The proper doping concentration of Gd3+or Pr3+was0.6and0.01, respectively. In order to improve the quality of white light, Gd3+doped YAG:Ce made the red shift of Ce3+emission, while for Pr3+doped YAG:Ce, a sharp red line was added into the yellow Ce emission.(2) The photoluminescence intensity of nano YAG:Ce, Gd increased obviously by surface modification of polyvinyl pyrrolidone (PVP). The proper concentration of PVP was1.37wt%. The results show that the steric hindrance effect of polyvinyl pyrrolidone leads to high dispersion and good crystallinity of Y3Al5O12:Ce3+, Gd3+nano-phosphors prepared with adding a proper weight percentages of polyvinyl pyrrolidone. Adding polyvinyl pyrrolidone is beneficial for the photoluminescence enhancement of the samples, which is attributed to the promotion of the incorporation of Ce3+and Gd3+into the Y3Al5O12nanocrystal and the surface passivation of the nano-particles by the PVP molecules.(3) Alkali metal metavanadate (AVO3) phosphors were prepared. The broad excitation spectra in the200-400nm UV range indicates the feasibility of AVO3phosphors to be utilized in ultraviolet light emitting diodes (UV-LEDs) or near UV-LEDs. Owing to their broad emission band, AVO3can be used as single-phased white light phosphors. The theoretical calculation and the experimental results show that AVO3have similar crystal structures and luminescence properties. The luminescence of AVO3phosphors is attributed to the charge-transfer transition from O2-to V5+in the VO4tetrahedra.(4) Among AVO3phosphors, CsVO3was selected as the material to be investigated with glycerol, polyethylene glycol, PVP as surface modifiers respectively. The surface modification with PVP or PEG can achieve better modification effect. Their proper concentration were2.10wt%. By studying the effect of surface encapsulation on photoluminescence properties of CSVO3, it can be concluded that when the ratio of cesium and silicon quality is1:6, CsVO3SiO2is obtained with good stability and photoluminescence properties. Direct fabrication of the CsVO3/P(S-MMA) film by in-suit dispersion polymerization would be advantageous not only in terms of cost, flexibility and process as well as steady luminescent properties but also to further expand potential applications.(5) Single-phased color-tunable phosphors for UV-LED or near UV-LED, Sm3+, Dy3+and Eu3+single doped or co-doped Sr2CeO4phosphors were synthesized. The theoretical calculation and the experimental results show that Eu3+and Dy3+co-doped Sr2Ce04phosphors can achieve better quality of white light. The proper concentration of Eu3+and Dy3+is0.03and0.006, respectively. Blue-white luminescence of Sr2CeO4under UV excitation is attributed to the radiative relaxation in two different charge transfer (CT) complex Ce4+-O2-. The energy transfer model clarifies the possible mechanisms of energy transfer from Sr2Ce04host to rare earth ions in Eu3+doped Sr2CeO4phosphors. Particularly, the PL mechanism in Eu3+and Dy3+co-doped Sr2CeO4should be fully explained by the energy transfer model with considering the defect conditions resulted from doped competition between different rare earth ions in crystals.