Preparing And Characterization Of Rare Earth-activated Oxynitride/Nitride Phosphors

Rare earth-activated oxynitride/nitride phosphors are potential white light LED fluorescence conversion materials with high efficiency and high stability. However, their synthesis conditions are very harsh. The demand of high calcination temperature and high operation presuure means high energy consumption and high equipment investment. In order to overcome this disadvantage, we employ some active elements or compounds, such as silicon powders rather then silicon nitride, as starting material to synthesize rare earth-activated oxynitride/nitride phosphors. The effects of Eu2+content, calcination temperature, reaction gas composition, fluxes on the luminescence property of as-synthesized phosphors were investigated and the optimal synthesis conditions were determined:Firstly, rare earth-activated oxynitride phosphors (SrSi2O2N2:Eu2+, SrSi2O2N2:Yb2+) were synthesized by a high temperature solid state reduction and nitridation reaction using silicon as staring material. The as-synthesized SrSi2O2N2:Eu2+phosphor emits strong green light at around550nm under excitation of300-500nm radiation. However, SrSi2O2N2:Yb2+phosphor emits weak red light at about610nm under the excitation of blue light at460nm. The phase of as-synthesized oxynitride phosphors SrSi2O2N2:Eu2+, SrSi2O2N2:Yb2+is pure and is consistent with that reported in literatures. Meanwhile, the effect of post treatment procedures of2N2:Eu2+phosphor on the luminescence intensity was evaluated. The results demonatrated that SrSi2O2N2:Eu2+showed high stability towards heat treatment below200℃.Secondly, Eu2+-activated nitride phosphors, Ca2Si5N8:Eu2+, CaAlSiN3:Eu2+with pure single phase were prepared at1400℃using silicon, aluminum and calcium hydride as main raw materials. The excitation band of Ca2Si5Ng:Eu2+red phosphor ranges from250nm to550nm, and the emission band ranges from500nm to750nm. Similarly, the excitation wavelength of CaAlSiN3:Eu2+red phosphor is in the range of from200nm to600nm, and the emission wavelength is within550nm and750nm. The red emission of as-synthesized phosphors is strong. This study was focused on the synthesis of rare earth-activated oxynitride/nitride phosphors at temperature below1400℃and atmospheric pressure by replacing inner material silicon nitride with active materials, such as silicon, aluminium and calcium higride. Compared with the tradition synthesis method using silicon nitride as main starting material, the method described here can be realized using current equipment conditions in existing luminescence material manufacture plants, and possess potential application value due to the obvious energy saving effect.