Spectroscopy of Cr3+ activator: Tanabe-Sugano diagram and Racah parameter analysis

The Racah parameters in conjunction with the Sugano-Tanabe energy-level diagram are used as a means of describing the effects of electron-electron repulsion within the metal complexes in coordination chemistry. A determination of the excitation energies in the 3d(3)-configuration ions like Cr3+ and Mn4+ is possible from a set of Racah (B and C) and crystal-field splitting parameters (Dq), and vice versa. However, it is very difficult to exactly determine some excitation-state energies that leads to a large error in the Racah parameter determination. The present study focuses on this problem and proposes a new model that introduces an optional Racah parameter ratio of C/B equivalent to r to make it possible without requiring an uncertain excited-state energy in the Racah parameter calculation. As a typical example, spectroscopic data of MgO:Cr3+ phosphor are investigated based on the present analysis model, where Cr3+ ions can be situated in cubic, tetragonal, and rhombic site of MgO lattice. The Racah parameters and related excited-state energies determined here are found to fall very well on each Tanabe-Sugano diagram curve (E-2(g), T-4(2g), T-2(1g), T-4(1g,a), T-2(2g), and (2)A(2g)). The present analysis model can be expanded to other 3d(3)-activated phosphor systems such as Mn4+ ion or fluoride hosts.

Automated summary

This study introduces a new model that includes an optional Racah parameter ratio to address the issue of large errors in determining Racah parameters due to uncertainties in excited-state energies. The model was successfully applied to the investigation of spectroscopic data for MgO:Cr3+ phosphor, demonstrating its potential for other 3d(3)-activated phosphor systems.