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Self-trapped electron and transient defect absorption in niobate and tungstate crystals

Abstract We have measured transient optical absorption in LiNbO3, KNbO3, PbWO4, CdWO4, and ZnWO4 following band-gap excitation by 200-fs laser pulses and by 10-ns electron pulses. A strong infrared transient absorption band centered near 1 eV was found in a sample of stoichiometric LiNbO3. We tentatively attribute this infrared absorption band to intrinsic electron polarons, following observation and EPR characterization of a similar (persistent) band in Mg-doped, thermochemically reduced congruent LiNbO3 by Schirmer et al‥ Socalled blue-light induced infrared absorption in KNbO3 was investigated by time-resolved spectroscopy as well. In PbWO4, CdWO4, and ZnWO4, broad, transient visible and infrared absorption bands are observed. It is considered whether infrared absorption in PbWO4 may be partly due to self-trapped electrons already characterized by Laguta et al. and Hofstaetter et al. using EPR.