Combustion synthesis and upconversion luminescence of CaSc sub(2O) sub(4):Yb[super]3+,Er[super]3+ nanopowders

Novel up-conversion (UC) luminescent nano-powders, CaSc sub(2O) sub(4):Yb[super]3+:Er[super]3+ were prepared with a combustion method at an ignition temperature as low as 200 [deg]C. The CaSc sub(2O) sub(4):Yb[super]3+,Er[super]3+ nano-powder had an orthorhombic CaFe sub(2O) sub(4)-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 [super]2H sub(11/2--[super]4I) sub(1)5/2, [super]4S sub(3/2--[super]4I) sub(1)5/2 and [super]4F sub(9/2--[super]4I) sub(1)5/2 transitions of Er[super]3+ under a 980 nm semiconductor laser excitation at room temperature. The optimized doping concentrations for Yb[super]3+ and Er[super]3+ 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.