Temperature dependence of optical band gap in ferroelectric Bi3.25La0.75Ti3O12 films determined by ultraviolet transmittance measurements

Optical properties of ferroelectric Bi3.25La0.75Ti3O12 (BLT) films on quartz have been investigated using ultraviolet-infrared transmittance spectra in the temperature range of 77-500 K. The spectra can be divided into three distinctive photon regions between 1.1 and 6.5 eV. It is found that the band gap E-g decreases from 3.88 to 3.77 eV with the temperature. The parameters a(B) and Theta(B) of the Bose-Einstein model are 30.3 meV and 218.7 K, respectively. The band narrowing coefficient dE(g)/dT is -2.65x10(-4) eV/K at room temperature. The present results can be crucial for future application of ferroelectric BLT-based electro-optic and high temperature optoelectronic devices. (C) 2007 American Institute of Physics.