Several Rare Earth Doped Tungstate Luminescent Materials For White LED

Recently,white light emitting diodes(LED)have been treated as a new generation of lighting source due to their high luminous efficacy,long life time and low power consumption.They have been widely used for indoor and street lighting.Nowadays,the method that use a blue LED to excite Y3Al5O15:Ce3+(YAG:Ce)yellow phosphor is the main approach for commercial white LED,but the white light obtained by this approach has drawbacks such as low color rendering index and high color temperature,which have limited its application.In addition,its emission color changes with the driving voltage and this would lead the color shift during its application.However,the white light obtained by using an ultraviolet(UV)and near ultraviolet(NUV)LED to excite luminescent materials is considered as a new solution and has drawn much attention because high color rendering index and lower color temperature could be achieved.Moreover,there is no color shift during its application.In this work,we have synthesized rare earth doped tungstate glasses and phosphors.Their luminescent properties under excitation at UV and NUV light have been studied,respectively.In addition,we have explored the possibilities of their application for white LED the obtained results have been summarized as follow:Dy3+ single and Dy3+/Tm3+ co-doped WO3-La2O3-B2O3 tungstate borate glasses were prepared by the melt quenching method.Under excitation at 351nm,the intensity of yellow emission band around 575nm of Dy3+ ions increased rapidly with the increment of WO3 content in the 0.5Dy2O3-xWO3-24.5La2O3-(75-x)B2O3(x= 0,15,25,50)glasses.When the WO3 content was 15mol%,pure white emission was achieved in this glass.For 1.5Dy2O3-yTm2O3-50WO3-(23.5-y)La2O3-25B2O3(y=0.2,0.3,0.4,0.5)glasses,the intensity of the emission band around 575nm of Dy3+ ions decreased slowly with the increment of Tm3+ concentration when they were excited at 355nm.Simultaneously,the color coordinate shifted to white region.Pure white light emission was obtained when the Tm3+ concentration was 0.4mol%.A series of Li3Ba2La3-x(WO4)8:xEu3+(LBLW:xEu3+)(x=0.15 0.6,1.2,...,3.0)red phosphors were synthesized by the high temperature solid state reaction.Under excitation at 395nm,these phosphors have intense red emission via the 5D0?7F2 transition of Eu3+ ions,and the emission intensity increases gradually with the increment of Eu3+ concentration and reaches the maximum when the Eu3+ substitutethe La3+ completely.The emission intensity of LBLW:3.0Eu3+ is 30 times higher than that of Y2O2S:Eu3+ under the same experimental condition.The internal quantum effiency foe LBLW:Eu3+ could reach about 95%.The temperature-dependent luminescence of LBLW:2.7Eu3+ shows the integrated emission intensity of the 5D0?7F2 transition at 450K decreases to 65%of that at room temperature.The activation energy(AE)from 5D0 to Eu3+-O2-charge transfer state band is 0.24eV.All the results indicate that the Dy3+ single and Dy3+/Tm3+ co-doped WO3-La2O3-B2O3 luminescent glasses and Eu3+ doped Li3Ba2La3(WO4)8 red phosphors could be excited by UV and NUV LED,repectively,and have potential applications in white LED.