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Suppression of photorefraction in hafnium-doped lithium niobate crystals

Lithium niobate crystals used in quantum electronics and integrated optics are mainly doped by different impurities in order to strengthen or suppress one or another property. Here we discuss the influence of hafnium impurity on photorefractive and photoelectric properties of lithium niobate crystals. The investigations of photorefractive effect in hafnium doped lithium niobate crystals have shown the possibility of suppression of photorefraction in these crystals (up to 3 orders). The experimental results demonstrate that the suppression of photorefraction occurs as a result of correlated increase of crystal dark and photo conductivities by 5 orders which is explained by significant increase of polaron mobility in the conduction band. One of the possible causes of the polaron mobility increase is the modification of the phonon spectrum of the crystal and a reduction of polaron scattering on defects associated with the lithium deficiency.