Green and red upconversion luminescence in Er 3+-doped and Er 3+/Yb 3+-codoped SrTiO 3 ultrafine powders

Abstract

Er 3+-doped and Er 3+/Yb 3+-codoped strontium titanate (SrTiO 3) ultrafine powders were prepared in a molten NaCl flux. The intense green and red emissions around 528 nm, 550 nm and 662 nm corresponding to the 2H 11/2 → 4I 15/2, 4S 3/2 → 4I 15/2 and 4F 9/2 → 4I 15/2 transitions, respectively, of Er 3+ ions were observed under excitation at 980 nm. A great enhancement of the visible upconversion emissions in Er 3+/Yb 3+-codoped sample was observed. Excited state absorption and energy transfer process are discussed as the possible mechanisms for these emissions.