Abstract
The optical absorption coefficients of orthorhombic V 2O 5 single crystals were evaluated using incident polarized light over the wavelength range 0.47–1·8μ, and in unpolarized light from 1·5 to 7·5μ. The intrinsic absorption edges were found to have an exponential dependence on photon energy. Fundamental absorption was observed at incident photon energies of 2·15, 2·22 and 2·17 eV for E∥ a, E∥ b and E∥ c, respectively. Some evidence for a direct forbidden transition mechanism with band gaps of 2·36 and 2·34 eV was observed for E∥ a and E∥ c, respectively. A double absorption peak was observed for the polarization E∥ a; the major peak occurs at 1·00 μ and the minor peak at 0·83 μ. Since this peak is completely missing in the absorption spectra when E∥ b and E∥ c, the mechanism associated with the absorption peak for E∥ a must itself be optically anisotropic. This double peak is associated with nonstoichiometric defects which act as donors. For wavelengths greater than 1·0μ there is an absence of absorption maxima until lattice or impurity absorption sets in at 4·4μ. A critical comparison of the results of this investigation with earlier studies of the optical properties of V 2O 5 is presented.
Published Version
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