Preparation And Properties Of Vanadate Phosphor For White LEDs

The Zn₃V₂O₈ phosphor materials were prepared by the combustion method at different temperatures?600?,650?,700?,750??.The crystal structure of the samples was determined by X-ray diffraction,and the surface morphology was measured by scanning electron microscopy.The excitation spectra and emission spectra were measured by fluorescence spectrometer.The results showed that the crystallinity of Zn₃V₂O₈ phosphor material prepared at 700?was the best.The materials prepared at 600?and 650?contained Zn₂V₂O₇ heterophase.Zn₂V₂O₇ reduced the luminescent properties of the material.Zn₃V₂O₈ is broad-band emission,and the emission width is between 400-700nm,and the phosphor has the strongest emission peak at 550nm,basically covering the visible light range;phosphor materials of(Zn_1-xLa_x)₃V₂O₈?x=0,0.001,0.01,0.1?series were prepared by high temperature solid-state reaction method.It was found that when the La-doping was 0.001mol,the prepared Zn₃V₂O₈:La phosphor has the best crystallinity and the best luminescence properties.With the increase of La-doping,the luminescence of Zn₃V₂O₈:La decreases.The energy bands,density of states,absorption spectra,and reflectivity of Zn₃V₂O₈,(Zn_1-x-x La_x)₃V₂O₈,Zn₂V₂O₇ and M₃V₂O₈?M=Mg,Sr?have been calculated based on density functional theory.The results showed that the band gap width of Zn₃V₂O₈ was 2.715eV.The spectrum begins in the visible region and has good absorption in the ultraviolet and near ultraviolet regions.High pressure conditions have reduced the band gap of Zn₃V₂O₈ and increased the absorption of ultraviolet and near ultraviolet light by Zn₃V₂O₈.The La-doping has a great influence on the optical properties of Zn₃V₂O₈.when the La-doping was 0.001mol,the luminous efficiency of Zn₃V₂O₈ decreases.Comparing with Zn₃V₂O₈,the band gap of Zn₂V₂O₇ is reduced.The ratio of V and O atoms in Zn₂V₂O₇ increases,resulting in enhanced the V-3d and O-2p states near the Fermi level.At the same time,the absorption coefficient of Zn₂V₂O₇ is lower than that of Zn₃V₂O₈ in the UV-NUV region.The electronic structure and optical properties of M₃V₂O₈?M=Mg,Sr?were simulated and calculated.The results showed that the emission spectra of these materials were all in the visible region and can act as good luminescent materials.The Zn₃V₂O₈ has better absorption in the UV-NUV region than the Mg₃V₂O₈ and Sr₃V₂O₈ phosphor materials.