Luminescence properties of Pr3+ and Ce3+ in KCaF3 single crystals

Abstract

The optical excitation and luminescence spectra of (Pr3+,Ce3+) ions in KCaF3 are presented. High-resolution excitation and emission spectra of Pr3+ and Ce3+ were measured at temperatures between 77 and 293K. First measurements of KCaF3:Ce3+ crystal show that there are nonequivalent Ce3+ centers which radiate either in UV or visible range. The major Ce3+ nonequivalent center in KCaF3 is Ce3+ ion in the site with tetragonal site symmetry (S4). Energy levels for the 4f2 ground configuration of Pr3+ in KCaF3 were established from excitation and fluorescence spectra. Energy levels assignments were made assuming electric-dipole transition selection rules for S4 site symmetry. Twenty-seven energy levels in the lowest six multiplets of the ground configuration were established. In the analysis of experimental data, the Oh magnetic-dipole selection rules were also considered to explain missing or weak transitions which are allowed in S4. Spectra of Pr3+ in KCaF3 have been analyzed with a crystal-field Hamiltonians of S4 or Oh symmetries including J mixing effects. Crystal-field parameters in these Hamiltonians have been determined by the minimization the RMS deviation between calculated and experimental energy Stark levels. We conclude that both model calculations in the S4 and Oh site symmetries for Pr3+ in KCaF3, provide the basis for a consistently good correlation with data.