Electro-optic and photorefractive properties of Bi_4Ge_3O_12 crystals in the ultraviolet spectral range

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Abstract
For the first time to our knowledge, photorefractive effects have been observed in the ultraviolet spectral region in undoped crystals of Bi4Ge3O12. For the investigation of the photorefractive properties we performed holographic experiments, and we further investigated fundamental properties, such as the photoconductivity and the dispersion of the electro-optic coefficients. Gain coefficients greatly exceeding the absorption losses and recording time constants ≈30 ms were observed in two-wave-mixing experiments with ultraviolet light in the 330–350-nm spectral region at a 0.5W/cm2 power level. The charge carriers primarily involved in charge transport are holes.