Investigation of the optoelectronic properties of columbite ZnNb2O6 crystal

A high-quality ZnNb2O6 single-crystal grown by optical floating zone method has been used as a research prototype to analyze the optoelectronic parameters by measuring the absorption coefficient and transmittance spectra along the b-axis from 200 nm to 1000 nm at room temperature. The optical interband transitions of ZnNb2O6 have been determined as a direct transition with a band gap of 3.84 eV. The refractive index, extinction coefficient, and real and imaginary parts of the complex dielectric constants as functions of the wavelength for ZnNb2O6 crystal are obtained from the measured absorption coefficients and transmittance spectra. In the Urbach tail of 3.16-3.60 eV, the validity of the Cauchy-Sellmeier equation has also been evaluated. Using the single effective oscillator model, the oscillator energy E-o is found to be 4.77 eV. The dispersion energy E-d is 26.88 eV and ZnNb2O6 crystal takes an ionic value. (C) 2014 Elsevier Ltd. All rights reserved.