Luminescent properties of Eu-doped germanate apatite Sr2La8(GeO4)O2

The photoluminescence properties of Eu-doped Sr2La8(GeO4)6O2 were investigated by measuring emission and excitation spectra, and decay curves. The Eu3+ ions were found to occupy two cationic sites labeled La(2) and Sr(1). The dominant sites La(2) occupied by Eu3+ ions shows strong red emission (5D0 → 7F2 transition) at 613 nm. The Eu3+ ions incorporated into the subordinate sites Sr(1) produces strong orange emission (5D0 → 7F1 transition) at 589 nm. This would be responsible for the charge-compensating mechanism, in which inversion symmetry is evident around the europium ions. The concentration quenching behaviors of excitation under CTS and intra-4f energy levels are different. The emission intensity decreases at the onset of about 15 mol% Eu3+ concentration under the excitation at CTS, and the saturation of emission intensity excited by intra-4f transitions occurs at a concentration of 50 mol% Eu3+. The maximum photoluminescence intensity of excited at intra-4f transitions is about a factor of 10 times brighter than that excited at CTS.