Low-temperature photoluminescence spectra of CdO–In2O3 thin films prepared by sol–gel

(CdO)1−x–(InO3/2)x thin films were deposited on glass substrates by the sol–gel method. The precursor solutions for the mixed oxide films were obtained from the mixture of the precursor solutions for CdO and In2O3 prepared separately. The investigated In atomic concentrations in the solution, x, were 0.0, 0.16, 0.33, 0.50, 0.67, 0.84, and 1. X-ray diffraction measurements showed that the films were mainly constituted of CdO, In2O3, and CdIn2O4. CdO and In2O3 were obtained for x=0 and 1, respectively. For x=0.67, which is the stoichiometric composition of the CdIn2O4 compound, only this oxide was formed. CdO and CdIn2O4 crystals were obtained in the Cd-rich region, whereas In2O3 and CdIn2O4 crystals were formed in the In-rich region. The PL spectra at 15 K for CdO showed the presence of two main emission bands at energies close to 2.2 and 3.0 eV. A blue-shift of these bands took place for increasing In concentration, which is related to the increase in the band gap energy of the mixed system in going from CdO, with a band gap energy of 2.46 eV, to CdIn2O4, with 3.2 eV, to In2O3, with 3.6 eV.