VCenters in Potassium Bromide Crystals

Physical Review1966Vol. 141(2), pp. 758–767

Abstract

The nature of $V$ centers stable at room temperature in KBr crystals has been investigated by means of preferential bleaching with polarized light. $V$ centers were produced by ionizing radiation, by electrolysis with a pointed anode, or by additive coloration with bromine at high pressure. In pure KBr crystals, the properties of $V$ centers depended on the method of production. Two absorption bands of $〈100〉$-type symmetry were formed at 253 and 278 m\ensuremath{\mu} both by electrolysis and by additive coloration, but no corresponding bands could be found in irradiated crystals. The main product of additive coloration was a broad absorption band extending from the fundamental absorption edge to 320 m\ensuremath{\mu}, appearing in all crystals, pure or doped, which is attributed to bromine molecules. It is suggested that this band forms a large part of the broad absorption band produced by prolonged irradiation of pure crystals, usually referred to as the ${V}_{2}$ and ${V}_{3}$ bands. Furthermore it was shown that the ${V}_{3}$ band is not caused by hydride ions. In KBr doped with alkaline-earth impurities an absorption band which does not depend on the method used to introduce $V$ centers appeared at 262 m\ensuremath{\mu} in KBr(Ca) and KBr(Sr) and at 267 m\ensuremath{\mu} in KBr(Ba). This band has $〈100〉$-type dichroism at 78\ifmmode^\circ\else\textdegree\fi{}K. Optical bleaching of this band at room temperature produced two overlapping bands arising from a common center with $〈111〉$-type dichroism at 78\ifmmode^\circ\else\textdegree\fi{}K. Possible models of the centers responsible for these bands are discussed.

Abstract

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