Defect pairs of F centers and substitutional H − ions ( U centers) in alkali …
1978; American Physical Society; Volume: 18; Issue: 4 Linguagem: Inglês
10.1103/physrevb.18.1868
ISSN1095-3795
Autores Tópico(s)Advanced Chemical Physics Studies
ResumoDefect pairs of $F$ and $U$ centers ["${F}_{H}({\mathrm{H}}^{\ensuremath{-}})$ centers"] were observed for the first time, created by laser-light induced aggregation of $F$ centers in NaCl, KCl, and RbCl crystals doped with high concentrations of substitutional ${\mathrm{H}}^{\ensuremath{-}}$ defects ($U$ centers). The formation of these pairs was indentified by the appearance of three sharp ${\mathrm{H}}^{\ensuremath{-}}$ local-mode lines in the Raman spectrum of $F$ centers (due to the replacement of one of the 12 ${\mathrm{Cl}}^{\ensuremath{-}}$ neighbors by a small-mass ${\mathrm{H}}^{\ensuremath{-}}$ ion). Raman studies of these local mode lines observed in different scattering geometries (${A}_{1g}, {E}_{g}, {T}_{2g}$) and in first and second order, reveal their symmetry and identify them as the three orthogonal linear vibrations of the ${\mathrm{H}}^{\ensuremath{-}}$ defect in a $〈110〉$ pair configuration with the $F$ center. A simple model, based on the Van der Waal interaction between the vibrating ${H}^{\ensuremath{-}}$ dipole and the induced electronic dipole at the $F$ center, explains well the observed local-model shifts. A speculative discussion is given on the absorption, emission, and photochemical properties of this pair formed from the two simplest prototypes of an electronic and local-model defect
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