Jahn–Teller effect and electron–phonon interaction in the 4T2g excited state of Cr3+ ion in K2LiAlF6 crystal

The electron–phonon coupling and Jahn–Teller effect in the first excited state 4T2g of Cr3+ in K2LiAlF6 crystal (which has the potential for tunable solid-state lasers applications) are considered. The force constants for the a1g and eg normal modes are calculated with the FG matrix method for the octahedral [CrF6]3− cluster and the Huang–Rhys factors Sa1g and Seg from the experimental value of the total Huang–Rhys factor and Stokes shift. Using these data, the changes of the metal–ligand bond lengths Δxeq,Δyeq=0.072Å (equatorial expansion) and Δzeq=−0.015Å (axial compression) were estimated. The Jahn–Teller stabilization energy has been evaluated from the contour plot of the 4T2g electronic state potential energy surface. The obtained results are compared with those for other fluorides; the common trends are found and discussed.