Electronic properties and 4f → 5d transitions in Ce-doped Lu2SiO5: a theoretical investigation

The electronic properties and the 4f -> 5d transitions of the dopant Ce3+ ions located at the two crystallographic lutetium sites of Lu2SiO5 (LSO) are investigated using the hybrid density functional theory (DFT) with the HSE06 functional and the wavefunction-based embedded cluster methods, respectively. The HSE06 calculations give a band gap of 6.35 eV for LSO, which agrees well with the reported experimental values between 6.4 and 6.8 eV. It is found that Ce3+ prefers strongly to occupy the seven-coordinated (Lu1) site over the six-coordinated (Lu2) one. The energy gaps between the occupied Ce3+ 4f band and the valence band maximum of the host are predicted to be 2.81 and 3.07 eV for Ce-Lu1 and Ce-Lu2 substitutions, respectively, which are close to the experimental data of 2.6-2.9 eV. Based on the wavefunction-based CASSCF/CASPT2 embedded cluster calculations for the energies of the Ce3+ 4f(1) and 5d(1) levels, the experimentally observed 4f -> 5d transition bands are identified in association with the two substitutions. The predicted transition energy and intensity patterns for Ce-Lu1 substitution are in fairly good agreement with those of the experimental absorption spectrum. The variations of the two lowest 4f -> 5d transition energies with the substitutions are finally discussed in terms of the changes of the centroid-energy difference and the crystal-field splitting with the local coordination geometries.