Luminescence and decay behaviors of Tb-doped yttrium silicate

The photoluminescence of terbium-activated yttrium silicate with the general formula Y2-xTbxSiO5 was investigated as a function of Tb3+ concentration. Especially, the main attention was focused on the D-5(3) fluorescence and its energy transfer behavior. The emission and excitation spectra were measured in terms of Tb3+ concentration. The diffuse reflectance spectrum was also measured in the range from VUV to UV. As a result, yttrium silicate was found to have a broad absorption band extended from the VUV to UV range. The concentration quenching was investigated in terms of luminance and decay time both for D-5(3) and D-5(4) fluorescence. The energy transfer was also investigated by analyzing the decay curve of D-5(3) emission on the basis of the multipolar interaction. The decay curves of D-5(3) emission, for which well-known cross-relaxation has been accepted as a main factor, were analyzed by Inokuti and Hirayama's formula on the basis of the direct quenching scheme. Furthermore, the rate equations including a newly proposed quenching scheme were taken into consideration. The rate equations accept the emission quenching as due to the cross-relaxation from D-5(3 or 4) to some upper levels such as D-7 and the charge-transfer band.