Synthesis And Characterization Of Tungstate And Molybdate Phosphors

In this paper, a series of solid solutions of Ca1-xYxW1-xNbxO4and Ca1-xYxMo1-xNbxO4were synthesized by Pechini sol-gel method, tungstate(CaWO4、SrWO4、BaWO4、PbWO4) phosphors were prepared by molten salt, and calcium tungstate was synthesized by hydrothermal method. The crystal structure, morphology and luminescent properties of these phosphors were discussed in detail.The crystal structure, morphology and luminescent properties were investigated using X-rays diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and photoluminescence spectra (PL), respectively.In solid solution of Ca1-xYxW1-xNbxO4, the optimum temperature and maximum doping amount(x) of NbO43-were800℃and25%, respectively. With the increase of x, the morphology changed from micro-cubes to micro-spheres with uniform size distribution. Upon the radiation of223nm ultraviolet, Ca0.75Y0.25W0.75Nb0.25O4shows blue emission with maximum at405nm, which is acribled to W-O charge transfer band in WO42-group. With the increase of x, the W-O charge transfer band shifts to high energy accompanying the decrease of luminescent intensity. In solid solution of Ca1-xYxMo1-xNbxO4, the optimum temperature and maximum doping amount(x) of NbO43-were1100℃and10%, respectively. The emission of CaMoO4was dominated by the510nm band emission originated from Mo-O transfer band in MoO42-group. With the increase of x, the Mo-O charge transfer band shifts to high energy accompanying the decrease of luminescent intensity.The tungstate (CaWO4. SrWO4、BaWO4、PbWO4) phosphors were synthesized by molten salt in equal moles of KNO3and NaNO3molten salt medium. XRD results indicated as-prepared tungstate were well assigned to the scheelite structure of tetragonal phase. The optimum reaction temperature was450℃, and CaWO4phosphors consisted of well dispersed crystals with narrow size distribution. Upon unltraviolet radiation, the emission of calcium tungstate emits blue light with maximum at420nm.CaWO4luminescent materials with good morphology were synthesized by hydrothermal process using polyvinylpyrrolidone (PVP) as protective agent at different pH values. The SEM results showed that as-prepared CaWO4phosphors with regular microspheres are about2.5μm in diameter.