Optoelectronic investigation of corundum Mg4Nb2O9 single crystal

The Mg4Nb2O9 crystals grown by floating zone technology were used as prototypes to investigate optoelectronic parameters by measuring the absorption and transmittance spectra along the c-axis from 200 to 800 nm at room-temperature. The imaginary and real parts of the complex dielectric constants, extinction coefficient and refractive index for Mg4Nb2O9 were obtained. The Cauchy-Sellmeier equation for Mg4Nb2O9 was validated in the Urbach tail region (4.0-5.0 eV). The dispersion energy Ed and oscillator energy E0 were obtained via the single oscillator approximation. More interestingly, the self-trapped exciton and disorder of Mg2+ and Nb5+ between MgO6 and NbO6 octahedrons participating in the transition in the Urbach tail region were confirmed by the excitation spectrum.