Photoluminescence in undoped (CdO)1−x–(InO3/2)x thin films at room temperature, 0≤x≤1

By means of the sol–gel growth technique undoped (CdO)1−x–(InO3/2)x thin films were prepared in the entire 0≤x≤1 range. The values of x studied 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 composed of CdO, In2O3, and CdIn2O4. CdO and In2O3 were obtained for x=0 and 1, respectively, and 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. X-ray diffraction, atomic force microscopy, UV–vis spectroscopy and photoluminescence (PL) measurements were carried out at room temperature for the material characterization. At x=0, i.e. for CdO, PL showed the presence of three main emission bands centered at energies 2.0, and 2.3 and 2.9 eV. Even with the fact that films do not form a continuous solid solution of CdO and In2O3 in all the 0≤x≤1 range studied, the material seems to have a graded evolution of these three bands observed in CdO as x moves from 0 to 1, that is from CdO to In2O3. The band at 2.0 eV has a red shift when x increases; on the contrary, a blue-shift of the bands at 2.3 and 2.9 eV takes place for increasing In concentration, which is related to the increase in the band-gap energy of the mixed system. Actually, this work is a continuation of a previous report of PL at low temperatures.