Structural, optical and photocatalytic properties of pure and Pd-doped CdS thin films

Pure and palladium (Pd)-doped cadmium sulfide (CdS) thin films were deposited on glass substrate by successive ionic layer adsorption and reaction (SILAR) process with different doping concentrations. X-ray diffraction results confirmed the crystalline and hexagonal phase structure of prepared samples. The increase in the main diffraction peak (002) intensity with increasing Pd concentration revealed the substitution of Pd⁺² with Cd⁺² in the lattice. The crystallite size increased from 58.32 to 89.71 nm with Pd concentration. Morphology of the thin films shown that the average grain size increases by the agglomeration of nano-grains which become cluster of particles after Pd⁺² incorporation. The energy bandgap of the CdS thin films is decreased from 2.44 to 2.37 eV with increasing Pd percentage. Photoluminescence (PL) spectra described that the pure and Pd-doped thin films show a broad PL emission peak associated to the transition of sulfur ion vacancy transfers to the valence band. Moreover, the Pd doping improved the film photostability as well as the photocatalytic degradation of methylene blue (MB).