LUMINESCENT PROPERTIES OF NONDOPED AND RARE-EARTH-METAL ION-DOPED K2LA2TI3O10 WITH LAYERED PEROVSKITE STRUCTURES - IMPORTANCE OF THE HOLE TRAP PROCESS

K2La2Ti3O10 with a layered perovskite structure showed photoluminescence at 475 nm by excitation at 315 nm at 77 K. On K2La2Ti3O10 doped with rare earth metal ions,luminescence of the rare earth metal ions was observed by the host excitation (K2La2Ti3O10). The efficiency of the energy transfer from the host to the rare earth ions led to the classification of the REMI-doped KLT into two groups. Luminescence of both the host and of the rare earth ions was observed on the Sm3+-, Dy3+-, Er3+-, and Tm3+-doped (1 mol % to La) K-2-La2Ti3O10 at 77 K by the host excitation. On the other hand, on Eu3+-, Tb3+-, and Pr3+-doped K2La2Ti3O10, the host luminescence was almost completely quenched, and only the luminescence of the rare earth metal ions was observed. For the latter cases, Eu3+, Tb3+, and Pr3+ showed their luminescence even at 300 K by the host excitation. Moreover, the Tb3+- and Pr3+-doped K2La2Ti3O10 showed long afterglows at 77 K and bright thermoluminescence. The long afterglows indicated the achievement of charge separation for a long time (> 10 min). It was concluded that the hole trap process accompanying the valency change of the Tb and Pr ions (3+ --> 4+) played an important role for the characteristic behaviors of the Tb3+- and Pr3+-doped K2La2Ti3O10.