Preparation, Characterization and Electroluminescence Studies of Cadmium Selenide Nanocrystals

Abstract

Nanoparticles of CdSe were prepared using chemical method by reacting cadmium acetate and sodium selenosulfite in presence of capping agent mercaptoacetic acid (MAA). Two-propanol was added to this mixture, drop wise, till it becomes turbid. The precipitate was separated through centrifugation to get dry powder. TEM shows that the most particles are spherical with particle size of the order of few nanometres. The XRD pattern indicates the hexagonal phase with wurtzite structure. The broadening of peaks tends to increase with increasing capping agent concentration showing decrease in particle size in range of 3 nm to 4 nm. Absorption spectra of CdSe nanoparticles indicated that the position of absorption peak shift to smaller wavelength as the capping agent concentration increases. Considering this as band-to-band absorption, their effective band gap was calculated and particle size was estimated using effective mass approximation, which is nearly same as obtained by XRD. The electroluminescence (EL) cells were prepared by placing CdSe nanoparticles between SnO2 coated conducting glass plate and aluminum foil. Alternating voltage of various frequencies was applied and EL brightness at different voltages was measured and corresponding current was also recorded. It is seen that emission starts at a threshold voltage and then increases rapidly with increasing voltage. The lower threshold and higher brightness have been observed for smaller nanoparticles. Linear relation between voltage and current indicates ohmic nature. Voltage vs brightness curve shows that EL is produced by acceleration-collision mechanism.