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Hole photoconductivity in KBr crystals containing Br−molecule ions

Journal of Physics and Chemistry of Solids
Publication Date
DOI: 10.1016/0022-3697(61)90278-5


Abstract After X-ray irradiation at liquid nitrogen temperature, holes are trapped by forming Br − 2 molecule ions in KBr containing one of the impurities Ag +, Tl +, Pb ++, or NO − 2. The Br − 2 molecule ions are oriented along 〈110〉 directions in the crystal and have two principal absorption bands at 385 mμ and 750 mμ, both of which show anisotropic properties. Irradiation into either one of these bands with [0 1 1] polarized light causes a redistribution of the ions among the six 〈110〉 directions in the crystal so that the population in [011] is considerably enhanced. Photoconductivity has been observed upon bleaching with light of 750 mμ wavelength. The bleaching light used was polarized along either [0 1 1] or [011]. Since continued bleaching at 750 mμ with [0 1 1] light causes a decrease in the absorption of [0 1 1] light, the observed photoconductivity decreases. If the plane of polarization of the bleaching light is rotated to [011], the photoconductivity rises and then decays to an equilibrium value. These changes in photoconductivity have been correlated with changes produced in the optical absorption spectra of Br − 2.

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