The effect of charge compensation by means of Na+ ions on the luminescence behavior of Sm3+-doped CaAl4O7 phosphor

Results of structural and spectroscopic measurements of Sm3+ doped calcium aluminates: Ca1−xSmxAl4O7 and Ca1−2xSmxNaxAl4O7 (x=0.0005, 0.002, 0.01, 0.02, 0.03, 0.05) obtained by the modified Pechini method are presented. All samples yield intense orange–red emission under violet excitation (404.5 nm). Narrow bands corresponding to characteristic f–f intraconfigurational transition of Sm3+ in excitation and emission spectra were observed. The influences of the concentration of Sm3+ as well as charge compensation by co-doping with Na+ ions on the luminescent properties of the phosphor were investigated. Detailed analysis of the emission spectra of Sm3+ doped and Sm3+,Na+ co-doped CaAl4O7 powders proved that activator ions substitute Ca2+ in the host. Co-doping with Na+ ions enhanced greatly the intensity of the luminescence. Concentration dependencies of the intensity of luminescence and its decay kinetics proved the emission quenching at higher dopant contents due to cross-relaxation processes between Sm3+ ions. Fitting of the 4G5/2 state fluorescence decay to the Inokuti–Hirayama model indicated dipole–dipole interaction as the dominant mechanism of the cross-relaxation processes.