Anomalous activity of Eu3+ in S6 site of Lu2O3 in persistent luminescence

Radioluminescence and persistent luminescence from Lu2O3 doped with Eu3+ ions (0.05–5%) were investigated. The radioluminescent emission is almost totally due to Eu3+ ions occupying the C2 symmetry site of Lu2O3 host, and the luminescence from Eu ions placed in S6 site makes only 1–3% of the total. However, Eu3+ ions occupying the S6 site becomes abnormally active in persistent luminescence. The effect reached its peak for 0.2% and 0.5% samples, for which the afterglow luminescence occurred mostly through Eu in the S6 site. This effect is indeed surprising, since only 25% of metal sites in Lu2O3 possess the S6 symmetry, while 75% sites are of the C2 symmetry. For strongly diluted materials containing less than 0.2% of the activator, the effect of unusually significant afterglow from Eu in S6 site becomes slightly less profound. For samples containing 3% and 5% of Eu this effect practically disappears.