Excited-state absorption spectra of V2+ in KMgF3 and MgF2.

Abstract

We have measured the excited-state absorption spectra of ${\mathrm{V}}^{2+}$ in ${\mathrm{KMgF}}_{3}$ and ${\mathrm{MgF}}_{2}$. The observed absorption bands can be identified as being due to the $^{4}\mathrm{T}_{2}$\ensuremath{\rightarrow}${\mathrm{}}^{4}$${\mathrm{T}}_{1}$a and $^{4}\mathrm{T}_{1}$b transitions. The position and shape of the $^{4}\mathrm{T}_{2}$\ensuremath{\rightarrow}${\mathrm{}}^{4}$${\mathrm{T}}_{1}$b transition are determined primarily by the displacement in the ${a}_{1g}$ mode while the coupling of the orbital triplet states to ${e}_{g}$ distortions is found to have a substantial influence on the nature of the $^{4}\mathrm{T}_{2}$\ensuremath{\rightarrow}${\mathrm{}}^{4}$${\mathrm{T}}_{1}$a transition. In fact, this transition is observed as a broad band rather than as a sharp line, as is predicted solely on the basis of the ${a}_{1g}$ coordinate. The $^{4}\mathrm{T}_{2}$\ensuremath{\rightarrow}${\mathrm{}}^{4}$${\mathrm{T}}_{1}$a transition is shifted up in energy relative to its predicted position and significantly overlaps the emission spectrum, thereby providing an explanation for the poor lasing efficiency reported for ${\mathrm{V}}^{2+}$ lasers.