A luminescence spectroscopy and theoretical study of 4f-5d transitions of Ce3+ ions in SrAlF5 crystals

This research is focused on the 4f-5d transitions in Ce3+ centers doped into tetragonal β-SrAlF5 single crystals belonging to the I41/a space group. The presence of four non-equivalent Sr2+ sites in this compound leads to the appearance of three spectroscopically non-equivalent Ce3+ luminescence centers, which can be well distinguished using a time-resolved laser spectroscopy technique. All 4f-5d transitions have slightly varying excitation and emission energies with characteristic probabilities resulting in several decay times that can be determined experimentally. One of these centers experiences strong perturbation due to a defect nearby, probably the O2- impurity ion substituting for the F- ion and acting as a charge compensator as well. Identification of these photoluminescence centers is performed using crystal field calculations. The crystal field parameters are calculated for two identified centers using the structural data for SrAlF5; diagonalization of the crystal field Hamiltonian results in obtaining the splitting of the Ce3+ 5d states. This method allows 'regular' unperturbed Ce3+ centers with selected Sr2+ sites to be assigned.