Light-induced charge transport properties of potassium niobate crystals doped with nickel

Abstract

Measurements of absorption, light-induced absorption changes, photoconductivity, and bulk photovoltaic currents are carried out for different light wavelengths and intensities with a potassium niobate crystal (KNbO3) containing 90 mol ppm Ni. Absorption bands around 2.1 and 2.7 eV are present. The band around 2.1 eV yields no significant contribution to the photoconductivity but causes appreciable bulk photovoltaic currents. The photoconductivity is larger than in KNbO3:Fe which makes KNbO3:Ni promising for holographic applications. A nonlinear intensity dependence of the photoconductivity and of the bulk photovoltaic current density indicates that more than one photorefractive level contribute to the charge transport processes. The bulk photovoltaic currents are negligible in usual holographic experiments.