STRUCTURE OF THE JAHN-TELLER DISTORTED CR2-CR BY ELECTRON-SPIN-ECHO ENVELOPE MODULATION( DEFECT IN SRF2)

Electron spin echoes have been obtained by two-pulse (pi/2-tau-pi) and three-pulse (pi/2-tau-pi/2-T-pi/2) experiments in the \+1]<---->\-1] EPR resonance transitions of the Jahn-Teller orthorhombically distorte d Cr2+ in SrF2:Cr. Particular emphasis is placed on the stimulated ele ctron spin envelope modulation (ESEEM). Since this system has a spin S =2 and the zero-held-splitting contribution is of the same order of ma gnitude as the electronic Zeeman term, a new formalism for analysis of the ESEEM has been developed, allowing us to extend the Mims formalis m for S=1/2 to more complex systems. Applying it to our results we hav e determined the superhyperfine (shf) interaction tensors of Cr2+ with the nearest-neighboring (NN), next-nearest-neighboring (NNN), and thi rd-shelf-neighboring fluoride ions, estimating the Cr2+-F- distances w ith the orthogonalized envelope function method. The defect model cons ists of four fluoride ions in the yz (110) defect plane which relax in wards to touch the Cr2+ ion. The remaining four fluoride ions relax ou twards to fit into the next Sr2+ ions case.