Abstract
Results of structural and spectroscopic measurements of Sm 3+ doped calcium aluminates: Ca 1− x Sm x Al 4O 7 and Ca 1−2 x Sm x Na x Al 4O 7 ( 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 Sm 3+ in excitation and emission spectra were observed. The influences of the concentration of Sm 3+ 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 Sm 3+ doped and Sm 3+,Na + co-doped CaAl 4O 7 powders proved that activator ions substitute Ca 2+ 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 Sm 3+ ions. Fitting of the 4G 5/2 state fluorescence decay to the Inokuti–Hirayama model indicated dipole–dipole interaction as the dominant mechanism of the cross-relaxation processes.
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