Jahn-Teller Distortions of Ag2+ Ions in SrF2 and CaF2 by Odd Modes

Abstract

An anistropic EPR spectrum of ${\mathrm{Ag}}^{2+}$ ions has been observed at 4.2 °K in single crystals of Ca${\mathrm{F}}_2$ and Sr${\mathrm{F}}_2$ that have been doped with silver. X rays convert the silver from the ${\mathrm{Ag}}^{1+}$ to the ${\mathrm{Ag}}^{2+}$ state. The results may be fitted with spin Hamiltonians with $S=\frac{1}{2}$, $g_{\parallel }=1.\mathrm{}997\pm 0.001$ and $g_{\perp }=2.\mathrm{}106\pm 0.001$ for Ca${\mathrm{F}}_2$, and $g_{\parallel }=1.\mathrm{}988\pm 0.001$ and $g_{\perp }=2.\mathrm{}130\pm 0.001$ for Sr${\mathrm{F}}_2$. Hyperfine interactions with the silver nucleus are not resolved, but are expected to be small from symmetry considerations. Hyperfine interactions with two equivalent fluorines are observed and have the characteristic 1: 2: 1 intensity ratio with $A_{\parallel }=58.\mathrm{}6\times {10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$ and $A_{\perp }=14.\mathrm{}5\times {10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$ for Ca${\mathrm{F}}_2$:${\mathrm{Ag}}^{2+}$, and $A_{\parallel }=30.\mathrm{}6\times {10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$ and $A_{\perp }=14.\mathrm{}6\times {10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$ for Sr${\mathrm{F}}_2$:${\mathrm{Ag}}^{2+}$. Additional hyperfine structure from four other fluorine nuclei can be resolved when the magnetic field is along a $〈110〉$ direction. Optical absorption bands are observed in the x-rayed Ca${\mathrm{F}}_2$:

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