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ABSTRACT: Chromium-doped [Formula: see text] and [Formula: see text] have been studied by both EPR and ENDOR spectroscopy. [Formula: see text] ions enter the fluorite structure in distorted substitution cation sites. In both matrices the distortion observed is tetragonal. X- and Q-band EPR measurements at temperatures between 4 and 300 K allowed us to determine the ion symmetry and the following spin-Hamiltonian parameters: [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] for [Formula: see text]; and [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] for [Formula: see text]. For [Formula: see text], the weak superhyperfine interaction of [Formula: see text] with the surrounding [Formula: see text] ions has been studied by both EPR and ENDOR techniques for [Formula: see text]. No ENDOR signals were detected for [Formula: see text]. The results are tentatively explained in terms of a Jahn - Teller effect corresponding to [Formula: see text] coupling strongly stabilized by lattice stresses, although other possible origins for the distortion cannot be completely ruled out.
Journal of Physics Condensed Matter 01/1999; 8(38):7179-90. · 2.55 Impact Factor
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ABSTRACT: Chromium-doped and have been studied by both EPR and ENDOR spectroscopy. ions enter the fluorite structure in distorted substitution cation sites. In both matrices the distortion observed is tetragonal. X- and Q-band EPR measurements at temperatures between 4 and 300 K allowed us to determine the ion symmetry and the following spin-Hamiltonian parameters: , , , and for ; and , , , , and for . For , the weak superhyperfine interaction of with the surrounding ions has been studied by both EPR and ENDOR techniques for . No ENDOR signals were detected for . The results are tentatively explained in terms of a Jahn - Teller effect corresponding to coupling strongly stabilized by lattice stresses, although other possible origins for the distortion cannot be completely ruled out.
Journal of Physics Condensed Matter 12/1998; 8(38):7179. · 2.55 Impact Factor
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ABSTRACT: Electron spin echoes on tetragonally distorted non-Kramers Cr2+ ions in chromium doped BaF2 and SrCl2 single crystals have been observed. The superhyperfine interaction (shf) with the nearest halide ions has been studied using
the electron spin echo envelope modulation (ESEEM) signal. For Cr2+ in BaF2 the nearest coordination shell consists of four equivalent fluorine ions in a plane perpendicular to the defect tetragonal
axis, the Cr2+ ion being off-centre displaced towards the fluorine plane. The Cr2+ shf tensor for BaF2 has been determined. For SrCl2:Cr ESEEM signals associated to the shf interaction with nearest chloride ions were observed but the measurements did not
allow us to give a definitive defect model in this case.
Applied Magnetic Resonance 05/1998; 15(2):155-168. · 0.75 Impact Factor
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ABSTRACT: Electron spin echoes have been obtained by two-pulse (π/2-τ-π) and three-pulse (π/2-τ-π/2-T-π/2) experiments in the |+1〉⇆|-1〉 EPR resonance transitions of the Jahn-Teller orthorhombically distorted Cr2+ in SrF2: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 Cr2+ with the nearest-neighboring (NN), next-nearest-neighboring (NNN), and third-shell-neighboring fluoride ions, estimating the Cr2+-F- 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 Cr2+ ion. The remaining four fluoride ions relax outwards to fit into the next Sr2+ ions cage. © 1996 The American Physical Society.
Phys. Rev. B. 10/1996; 54(17).
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ABSTRACT: Cr2O3 and CrF3 doped CaF2 single crystals have been studied by cw-EPR and electron spin echo envelope modulation (ESEEM) techniques. In both cases Cr2+ ions enter the fluorite structure at substitutionally distorted cation sites. For Cr2O3 doped crystals, X and Q band EPR measurements at temperatures between 4 and 200 K allowed us to determine the ion symmetry and spin Hamiltonian parameters, such as the g factors and the zero-field splitting tensors, as well as the 53Cr2+ hyperfine tensor. Electron spin echoes (ESE) were detected on that system at temperatures below 20 K. The analysis of the ESEEM and cw-EPR superhyperfine (shf) structure lead us to propose a model composed of two nearest-neighbor fluoride ions placed in the (110) plane containing the C2 axis with the ones opposite substituted by an O2- ion. For CrF3 doped crystals the distortion is also orthorhombic but the shf interaction is with four fluoride ions presumably in the (110) plane perpendicular to the z defect axis. No ESE was detected for this system. A linewidth narrowing effect was observed. We assign this distortion to a dynamical Jahn-Teller effect corresponding to T2g⊗(tg+eg) coupling stabilized by lattice stresses. © 1996 The American Physical Society.
Phys. Rev. B. 01/1996; 53(6).
