Optical spectra and analysis for Pr3+ in SrAl12O19

Abstract

Energy levels of the 4f² electronic configuration of Pr³⁺ in SrAl₁₂O₁₉ (SAM) have been determined from polarized absorption and fluorescence spectra using crystals, charge-compensated with Mg²⁺, at temperatures between about 20 and 300 K. Energy level assignments were made initially by comparing the crystal spectra with energy levels calculated by using crystal-field parameters, B_km, compatible with those previously reported for Nd³⁺ in SAM. The B_km were varied to obtain a best fit between experimental and theoretical energies, and the final values: B₂₀=−94, B₄₀=1047, B₆₀=−1397, and B₆₆=−1245 cm⁻¹ give an rms fit of 14.5 cm⁻¹. The B_km for Pr³⁺ in SAM were also used along with a result relating the B_km to crystal-field components, A_nm, derived in a lattice sum calculation to obtain B_km values for all the triply ionized rare-earth ions in SAM. Odd-fold A_km are also given that are required in the intensity and lifetime calculations and yield results in good agreement with the measurements. In addition, the results of our energy level fitting were useful in estimating absorption and emission cross sections, as well as lifetimes and branching ratios, for the various J multiplets. The evidence given here that the room temperature fluorescence quantum efficiency of ${}^3{P}_0$ in lightly doped Pr in SAM is near unity strengthens the case that this is a potentially useful laser material. The theoretical model and method of analysis used is useful for the calculation of energy levels, wave functions, transition probabilities, etc., for any rare-earth RE³⁺ ion in any host of known crystal structure.