Identification of local structures around Ce3+ centers in potassium magnesium fluoride

Several Ce3+ centers were experimentally found in Ce3+-doped potassium magnesium fluoride (KMgF3) crystal by electron-spin resonance (ESR) spectra, but there was no definite conclusion about the charge-compensating mechanism. In the present work, we carried out a comprehensive investigation on local structures around Ce3+ centers in the host, based on a combination of first-principles calculations and phenomenological analyses. The site occupation preference, crystal-field energy levels and spectral parameters (e.g. crystal-field parameters, and g factors) for Ce3+ ions in the host were derived, which are compatible with previously measured excitation and ESR spectra. Accordingly, four Ce3+ centers (at K+ sites) observed in ESR spectra are assigned successfully. In particular, the Ce3+ center previously thought to be associated with a Mg2+ site is reassigned to a K+ site, in agreement with the results of defect formation energy calculations. The presented calculations together with optical and ESR spectroscopy techniques may offer cross check for reliable determination of impurity sites in luminescent materials.