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In glassy Ge28.5Pb₁₅S56.5 films, we observed and studied the phenomenon of transient photorefraction---a change in refractive index during light irradiation, which is not accompanied by metastable photodarkening. Some possibilities for the explanation of this phenomenon are pointed out, and this phenomenon is claimed to be typical of films of many chalcogenide glassy semiconductors.
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Lyubin et al. (2008) studied this question.
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