Studies On Synthesis Of CdSe By Aqueous Solution Method

Metal chalcogenide as an important kind of semiconductor materials have a wide application prospect in many fields due to their unique physical, chemical properties. In particular, the optical, electrical and magnetic properties have been developed by altering their structure, dimension or morphology in recent ten years. In this paper, CdSe crystals were prepared through aqueous solutions using cadmium nitrate and sodium selenite as precursors, ammonia and EDTA as complexing agents, N2H4?H2O as a reducing agent. XRD, EDS, XPS, TEM, SEM, HRTEM and UV-vis were utilized to characterize chemical composition, crystal structures, morphology and optical properties of the CdSe crystals.Effects of processing parameters including complexing agents, refluxing time, concentration of Cd2+, the Cd/Se ratios and the stabilizers such as PEG4000, sodium citrate and thioglycolic acid were mainly investigated. The chalating action of EDTA and ammonia in dynamics of synthetical reaction was also discussed. Experimental results showed that the zinc blende and wurtzite CdSe crystals were obtained in the solution systems respectively containing EDTA and ammonia as complexing agents. When Cd2+ concentration of the solution with ammonia chalating was higher than 0.15mol/L and lower than 0.05mol/L, less CdSeO3 and Se beside CdSe main phase were found respectively. The ratio of Cd/Se played an important role in controlling the size and morphology of CdSe. The crystal sizes increased with the Cd/Se ratio in the range from 1 to 3. A branch crystal was formed as the Cd/Se ratio was more than 4. The stoichiometrical ratio of cadmium and selenium for the zinc blende and wurtzite CdSe crystals were 1:1 and 3:2 respectively according to EDS analysis. XPS spectra showed that Cd(OH)2 and SeOx(x≤1) compounds were easy to be formed on the surface of CdSe crystals from solution without stabilizers. Calculated from the UV-vis reflection spectra, the optical band gap of the zinc blende and wurtzite CdSe crystal was 1.63eV and 1.70eV respectively, no indicating the quantum confinement effect due to larger sizes of CdSe than the diameter of Bohr exciton in CdSe.