Crystal-Field Spectra of d3,7 Ions. VII. Cr3+ in K2NaGaF6

The ${}^4{T}_{\text{2g}}$ level of Cr³⁺ in K₂NaCrF₆ and in K₂NaGaF₆:Cr³⁺ is strongly mixed with the ${}^2{E}_g$ and ${}^2{T}_{\text{2g}}$ levels by spin–orbit coupling in the six‐coordinated cubic ${\mathrm{(O}}_h)$ site. The observed band profile for absorption and fluorescence in the transitions ${}^4{A}_{\text{2g}}{\mathrm{\hspace{0.17em}\leftrightarrow \hspace{0.17em}}}^4{T}_{\text{2g}}$ in the dilute system shows remarkably well‐resolved vibrational band progressions which have been analyzed in terms of a totally symmetric vibration at 568 cm⁻¹ (556 cm⁻¹ for the excited state) and a large number of nontotally symmetric vibrations ranging from 25–961 cm⁻¹.