Structure of the Jahn-Teller distorted Cr2+ defect in SrF2:Cr by electron-spin-echo envelope modulation.

Abstract

Electron spin echoes have been obtained by two-pulse (\ensuremath{\pi}/2-\ensuremath{\tau}-\ensuremath{\pi}) and three-pulse (\ensuremath{\pi}/2-\ensuremath{\tau}-\ensuremath{\pi}/2-T-\ensuremath{\pi}/2) experiments in the |+1〉\ensuremath{\leftrightarrows}|-1〉 EPR resonance transitions of the Jahn-Teller orthorhombically distorted ${\mathrm{Cr}}^{2+}$ in ${\mathrm{SrF}}_{2}$:Cr. Particular emphasis is placed on the stimulated electron spin envelope modulation (ESEEM). Since this system has a spin S=2 and the zero-field-splitting contribution is of the same order of magnitude as the electronic Zeeman term, a new formalism for analysis of the ESEEM has been developed, allowing us to extend the Mims formalism for S=1/2 to more complex systems. Applying it to our results we have determined the superhyperfine (shf) interaction tensors of ${\mathrm{Cr}}^{2+}$ with the nearest-neighboring (NN), next-nearest-neighboring (NNN), and third-shell-neighboring fluoride ions, estimating the ${\mathrm{Cr}}^{2+}$-${\mathrm{F}}^{\mathrm{\ensuremath{-}}}$ distances with the orthogonalized envelope function method. The defect model consists of four fluoride ions in the yz (110) defect plane which relax inwards to touch the ${\mathrm{Cr}}^{2+}$ ion. The remaining four fluoride ions relax outwards to fit into the next ${\mathrm{Sr}}^{2+}$ ions cage. \textcopyright{} 1996 The American Physical Society.