Synthesis And Luminescence Properties Of M_xSiO_2+x:RE?1<x?3?Phosphor For White LEDs

In this paper,several kinds of silicate phosphors were synthesized by high temperature solid state methods and sol-gel methods.Their crystal structure were identified by X ray diffraction?XRD?analysis and optical properties were characteried by spectral analysis.The energy transfer between Sm³⁺ and Eu²⁺ were discussed and the reduction mechanism of Eu³⁺ were studied.The results indicated that the luminescence intensity could be strenghted and luminescence spectra could be tuned by different synthesis technologies and co-doping Sm³⁺.1.Sr₃SiO₅:Eu²⁺ and Sr₃SiO₅:Eu²⁺,Sm³⁺ phosphors were synthesized by solid state methods.The single phase could be obtained by using nano-SiO₂ as silica source material and atomic concentration of Sr/Si=3.3.Under UV light excitation,Sr₃SiO₅:Eu²⁺ phosphor had two emission peaks at 468 nm and 565 nm.The optimal concentration of Eu²⁺ was 8mol%.Addition of SrCl₂?6H₂O flux effectively improved the luminescence property and made spectra red-shifted.Addition of Sm³⁺ contributed to Sr₃SiO₅ phase formation and Sm³⁺?Eu²⁺ energy transfer.The excitation spectra were overlapped by absorption of Sm³⁺ and Eu²⁺;The emission spectra located at 466nm?Eu????and 566nm?Eu????.Through Sr₃SiO₅ crystal structure,we found that the Sr???cells were space spiral structure that distorted seriously far more than areal distributive Sr???cells.Thus,the blue emission was sensitive to UV light;but orange emission could be excited from UV to visual light.The Eu²⁺ luminescence intensity were enhanced by Sm³⁺?Eu²⁺ energy transfer,especially with 1.5mol%Sm³⁺ addition.Besides,the co-doped Sm³⁺ changed the crystal field and led to spectra shifts.2.Sr₃SiO₅:Eu²⁺ phosphor was synthesized by sol-gel method.High purity Sr₃SiO₅ was obtained when citric acid?CA?amounts was 1.5wt%.The emission spectra was broadband located at 567 nm,which was improved apparently as CA concentration increased from1.0wt% to 1.5wt%.The LED lamp encapsulated by 390 nm chips produced 581 nm orange light emitting.The main emission and its FWHM were enhanced by 45% and 3nm,respectively.When CA content increased from 1.0wt% 1.5wt%,CIE coordinates changed from?0.4901,0.4649?to?0.4877,0.4832?,the light color purity was improved and warmer light was obtained.3.Sr₂SiO₄:Eu²⁺ and Sr₂SiO₄:Eu²⁺,Sm³⁺ phosphors were synthesized by solid state methods.Eu²⁺ promoted ????-Sr₂SiO₄ phase transformation;luminescence intensity approached to the best at 0.75mol%Eu²⁺;As excitation wavelength increased,the main emission was tuned from blue?Eu???site?to green-yellow band?Eu???site?.After Sm³⁺ added,the Eu³⁺ in phosphor reduced to Eu²⁺,the reduction mechanism was that replace of Sm³⁺ produced extra positive vacancies and negative defects,which contributing to Eu³⁺ reduction.Sm³⁺ promoted ?? formation,redshift of emission spectra and suppressed Eu???emitting;when Sm³⁺ concentration was 10mol%,existence of ? and less Eu???substituted by Sm³⁺ made luminescence intensity stronger.