Green and red upconversion luminescence in Er3+-doped and Er3+/Yb3+-codoped SrTiO3 ultrafine powders

Er3+-doped and Er3+/Yb3+-codoped strontium titanate (SrTiO3) 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 2H11/2 → 4I15/2, 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions, respectively, of Er3+ ions were observed under excitation at 980 nm. A great enhancement of the visible upconversion emissions in Er3+/Yb3+-codoped sample was observed. Excited state absorption and energy transfer process are discussed as the possible mechanisms for these emissions.