Temperature dependence of optical band gap in ferroelectric Bi_(3.25)La_(0.75)Ti_3O_(12) films determined by ultraviolet transmittance measurements

摘要

Optical properties of ferroelectric Bi_(3.25)La_(0.75)Ti_3O_(12) (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 Θ_B of the Bose-Einstein model are 30.3 meV and 218.7 K, respectively. The band narrowing coefficient dE_g/dT is -2.65 × 10~(-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.