A novel yellow-emitting SrAlSi_4N_7:Ce~(3+) phosphor for solid state lighting: Synthesis, electronic structure and photoluminescence properties

摘要

Ce~(3+)-doped and Ce~(3+)/Li~+-codoped SrAlSi4N7 phosphors were synthesized by gas pressure sintering of powder mixtures of Sr_3N_2, AlN, α-Si_3N_4, CeN and Li_3N. The phase purity, electronic crystal structure, photoluminescence properties of SrAlSi _4N_7:Ce~(3+)(Ce~(3+)/Li~+) were investigated in this work. The band structure calculated by the DMol~3 code shows that SrAlSi_4N_7 has a direct band gap of 3.87 eV. The single crystal analysis of Ce~(3+)-doped SrAlSi _4N_7 indicates a disordered Si/Al distribution and nitrogen vacnacy defects. SrAlSi_4N_7 was identified as a major phase of the fired powders, and Sr_5Al_5Si _(21)N_(35)O_2 and AlN as minor phases. Both Ce ~(3+) and Ce~(3+)/Li~+ doped SrAlSi_4N _7 phosphors can be efficiently excited by near-UV or blue light and show a broadband yellow emission peaking around 565 nm. A highest external quantum efficiency of 38.3% under the 450 nm excitation was observed for the Ce~(3+)/Li~+-doped SrAlSi_4N_7 (5 mol%). A white light LED lamp with color temperature of 6300 K and color rendering index of Ra=78 was achieved by combining Sr_(0.97)Al_(1.03)Si _(3.997)N94maccounttest14=t0005-18193 _7:Ce ~(3+) 0.03 with a commercial blue InGaN chip. It indicates that SrAlSi_4N_7:Ce~(3+) is a promising yellow emitting down-conversion phosphor for white LEDs.