Combustion synthesis and upconversion luminescence of CaSc2O4:Yb3+,Er3+ nanopowders

Novel up-conversion (UC) luminescent nano-powders, CaSc2O4:Yb3+:Er3+ were prepared with a combustion method at an ignition temperature as low as 200 °C. The CaSc2O4:Yb3+,Er3+ nano-powder had an orthorhombic CaFe2O4-type structure, and showed sphere-like morphology with an average diameter of about 30 nm. It gave strong green (525, 552 nm) and red (652-674 nm) up-conversion luminescence due to the 2H11/2→4I15/2, 4S3/2→4I15/2 and 4F9/2→4I15/2 transitions of Er3+ under a 980 nm semiconductor laser excitation at room temperature. The optimized doping concentrations for Yb3+ and Er3+ were 6.0 mol.% and 1.0 mol.%, respectively. Effects of ignition temperature and glycine-to-metal nitrate molar ratio on up-conversion emission intensity were also investigated. The log-log plots of luminescence intensity and pump power revealed that the 652-674 nm red emissions and 552 nm green emissions belonged to a two-photon process, while the 525 nm green emissions belonged to a three-photon process. The possible UC mechanisms were briefly discussed.