Characterization and Optical Transition in Tb-Doped 12CaO•7Al2O3 Powders

Tb-doped 12CaO center dot 7Al(2)O(3) (C12A7:Tb3+) powders with strong green emission were prepared using the sol-gel method. X-ray diffraction, micro-Raman spectra, scanning electron microscopy and absorption spectra showed that C12A7:Tb3+ powders with grain size of 200-300 nm were synthesized. Porous powders could be formed as the concentration of Tb3+ was 5 at%. The absorption band around 209 nm was attributed to the host lattice absorption, and the bands around 255 nm and 274 nm were related to the 4f-5d transitions of Tb3+. The absorption intensity of the visible region was enhanced due to the presence of one 100 nm-diameter hole in every grain of C12A7:Tb3+ powders. The emission spectra showed noticeable influence of Tb-Tb cross relaxation, which favored the green photoluminescence (PL) over the blue PL. The study on the concentration quenching indicated that the energy transfers depopulating the D-5(3) and D-5(4) levels were assigned to the mechanisms of electric dipole-dipole and exchange interaction, respectively.