Optical properties of La2CuO4 and La2-xCaxCuO4 crystallites in UV-vis-NIR region synthesized by sol-gel process

La(2)Cua(4) and La2-xCaxCuO4 crystallites were prepared via a simple sol-gel process. The as-prepared La(2)Cua(4) and La2-xCaxCuO4 crystallites were characterized by X-ray diffraction, transmission electron microscope and UV-vis-NIR spectra. Results show that the grain size of La2CuO4 crystallites increases with the increase of heat treatment temperature from 600 degrees C to 800 degrees C. Optical properties show that La2CuO4 crystallites have broad absorption both in the UV-vis region and in the NIR region. The band gap of the as-prepared crystallites decreases from 1.367 eV to 1.284 eV with the increase of calcination temperature from 600 degrees C to 800 degrees C. In the series of La2-xCaxCuO4 compounds (x=0.05, 0.08, 0.10, 0.12, 0.15 and 0.20), all of the samples exhibit an orthogonal crystal structure and the solubility limit of Ca2+ in La2CuO4 is within the range of x=0.12-0.15. In the whole UV-vis-NIR region, La2-xCaxCuO4 crystallites exhibit a broad absorption and the corresponding band gap first increases and then decreases with increasing of Ca2+ content. (C) 2011 Elsevier Inc. All rights reserved.