Long-term energy storage and thermoluminescence in phosphors based on cubic Lu2O3:Pr are achievable via introduction of d metal co-dopants. It was assumed from the vast experimental data that by photoionization of Pr3+ to Pr4+ occurs, and that d orbitals of the co-dopants contain (trap) the electrons formed upon excitation.

The experiments indicate two mechanisms of the electron release: an excitation to conduction band with the following recombination at Pr site, or a tunneling mechanism which does not involve conduction band. Given the fact that Lu states were not considered (i.e. no conduction band model was provided) – the results should be viewed as the tunneling trap depth. However, they might also be relevant to the mechanism with the band.

We have used RASSCF / CASPT2 / RASSI-SO (PrO69– cluster, Pr3+; PrO68– cluster, Pr4+; MO69– clusters, M3+, M=Ti, Zr, Hf) and CCSD (MO68– clusters, M4+) in order to obtain the total energies of the mentioned clusters of metal cations and their surrounding oxygens. The clusters were embedded in the c-Lu2O3 lattice by Ab Initio Model Potential (AIMP) and a sphere of point charges. For each cluster, total electronic energies were calculated for a series of geometries corresponding to a path along a certain vibrational normal mode. The total energy of the state with the trapped electron was represented by a sum of the energies of PrO68– and MO69– clusters (a Pr4+, M3+ system). The total energy of the state without the trapped electron was represented by a sum of the energies of PrO69– and MO68– clusters (a Pr3+, M4+ system).