Luminescence efficiency enhancement by impurity doping in SrIn2O4: Pr3+

A red-emitting phosphor, SrIn2O4:Pr3+ is a candidate of Cd-free phosphor for vacuum fluorescent tubes. Luminescence of SrxIn2O4:Pr3+ is quenched at a Sr-rich composition (x >= 1) by formation of defects that work as nonradiative centers. At the stoichiometric composition (x = 1.0), the luminescence efficiency is increased by addition of Gd3+, while decreased by La3+ addition. Measurement of the unit cell volume showed that Pr3+ and Gd3+ occupy the In3+ site, while La3+ presumably occupies the Sr2+ site. This site preference shifts the atomic ratio of the Sr/In site to the Sr-poor side by Gd3+ doping and to the Sr-rich side by La3+ doping, resulting in an increase or a decrease in efficiency at the stoichiometric composition. Under 1.4 keV electron excitation and at the dopant concentration of 7 atom % per 1 mol. SrIn2O4, Gd3+ doping provides the maximum efficiency about twice higher than the maximum efficiency of an undoped sample. The optimized Sr fraction for La3+ doping, x = 0.8, has led to efficiency about 2.7 times as high as efficiency of the undoped SrIn2O4:Pr3+. (c) 2006 The Electrochemical Society.