The Best Approximate Racah Parameter Ratio: r=C/B=3.7 (free-ion value), 4.7 or 8.0 for the Mn4+-Activated Phosphors?

Abstract The 3d3-configuration ions, such as Mn4+ and Cr3+, are very important for use in the warm white-LED lighting and indoor plant cultivation applications. The Racah parameters in conjunction with the TanabeSugano (TS) energy-level diagram are widely used as a means of deep understanding the effects of electronelectron repulsion within the transition metal complexes in coordination chemistry. In a TS diagram, the Racah parameter ratio of r=C/B is assumed and the excited-state transition energies are plotted as a function of the crystal-field strength parameter (Dq). Once the Racah parameters are determined, more refined comparison is made between theory and experiment and more accurate Racha and related parameter values are deduced. The present investigation examines in detail the effects of r=C/B ratio on the TS diagram analysis results for some Mn4+-activated fluoride and oxide phosphors. A newly proposed analysis model is comparatively discussed with the popularly used model. Results suggest that an assumption of r=8.0 successfully explains the luminescence properties of the Mn4+-activated fluoride phosphors very well. Contrarily, no large difference in the analysis results of the Mn4+-activated oxide phosphors can be obtained between r=4.7 and 8.0 though, if anything, the latter assumed value of 8.0 is slightly better.