Photoluminescence studies on Eu2+-activated Li2SrSiO4 -: a potential orange-yellow phosphor for solid-state lighting

A series of Eu2+-activated Li2SrSiO4 orange-yellow phosphor compositions exhibiting intense emission under 400-470 nm excitation are synthesized by solid-state reaction, and their luminescence properties are investigated as a function of activator concentration (Eu2+). The critical concentration is found to be 0.005 mol of Eu2+ (R-c = 34 angstrom) per formula unit. The composition containing 0.005 mol of Eu2+ is also synthesized by a combustion technique followed by postannealing at different temperatures. The luminescence emission intensity of a combustion-synthesized sample increases with increasing annealing temperature. This is attributed to increased crystallinity and improved distribution of activator in the lattice in the combustion-synthesized sample. Attempts are made to develop white light-emitting diodes by combining an InGaN blue LED chip (420 nm) and a Li2SrSiO4:Eu2+ phosphor. Two distinct emission bands from the InGaN and Li2SrSiO4:Eu2+ (562 nm) are observed that combine to give a spectrum that appears white to the naked eye. The values of the CIE coordinates indicate that the Li2SrSiO4:Eu(2+)coated LED has improved red emission compared to the commercial YAG:Ce phosphor.