Electro-plating and characterisation of cadmium sulphide thin films using ammonium thiosulphate as the sulphur source

Cadmium sulphide (CdS) thin films have been successfully prepared from an aqueous electrolyte bath containing CdCl2 and ammonium thiosulphate ((NH4)2S2O3) using electrodeposition technique. The structural, compositional, optical, morphological and electrical properties of these thin films have been characterized using X-ray diffraction (XRD), Raman spectroscopy, energy dispersive X-ray spectroscopy, UV–Vis spectrophotometry, scanning electron microscopy (SEM), atomic force microscopy (AFM), photoelectrochemical cell and D.C. current–voltage (I–V) measurements. The optimum deposition cathodic potential has been observed at 1,455 mV, in a 2-electrode system with respect to carbon anode. Structural analysis using XRD shows a mixture of hexagonal and cubic phases in the as-deposited CdS samples and a phase transformation to the hexagonal structure occurred after heat treatment at 400 °C for 20 min. Optical studies demonstrate an improvement in the band edge, producing 2.42 eV for the band gap of the films after heat treatment. The heat treated CdS thin films show better transmission for wavelengths longer than 500 nm. SEM and AFM show that the heat-treated samples are more uniform, smoother and have larger grain size. Electrical studies confirm that the CdS thin films have n-type electrical conductivity and heat treated CdS thin films have resistivities of the order of 105 Ω cm

Persistent near infrared phosphorescence from rare earth ions Co-doped strontium aluminate phosphors

Sr Al2 O4 phosphors co-doped with Eu2+, Dy3+, and Nd3+ ions are synthesized through a citric acid assisted sol-gel combustion process. The crystalline phases and crystallinity of the synthesized phosphors are studied by X-ray diffraction analysis. Strong persistent phosphorescence at 882 nm is observed as a consequence of irradiation by ultraviolet light at 370 nm due to the persistent energy transfer from excited Eu2+ ions to Nd3+ ions. The optimum doping concentration of Nd3+ ions is estimated to be ∼2%, when the concentration of Eu2+ and Dy3+ ions are 1 and 1.5%, respectively, considering the energy transfer efficiency and the near infrared phosphorescence intensity. © 2010 The Electrochemical Society