The excited state dynamics of KLa(MoO4)2:Pr3+: From a case study to the determination of the energy levels of rare earth impurities relative to the bandgap in oxidising host lattices

The luminescence properties of KLa(MoO4)2 (KLM) single crystals doped with Pr3+ have been measured in the 10–600 K temperature range in order to investigate the mechanisms involved in the radiationless processes. At variance with previously studied scheelite-like molybdates activated with Pr3+, no effects attributed to the formation of intervalence charge transfer states have been observed. The model proposed in order to account for this behaviour allows the determination of the energy of the Pr3+ levels relative to the valence and conduction bands of the host. This model has firstly been confirmed for Tb3+-doped KLM, for which suitable experimental data are available, and then extended to the other rare earth ions on the basis of the systematic nature of the lanthanide energy levels properties. The obtained conclusions are finally supported in the light of the comparison with some other representative cases.