Influence of the Particle Size on the Optical Properties of CdSe Nanoparticles

Monodispersed CdSe nanoparticles with sufficient luminescence intensity have been prepared by chemical method in the presence of mercaptoacetic acid as a capping agent. Cadmium acetate (Cd(Ac)2.2H2O) and sodium selenosulfate (Na2SeSO3) are used as a cadmium and selenium sources respectively. The resulting nanocrystallites have been characterized by X-Ray Diffraction, UV-Vis absorption spectra and photoluminescence (PL) spectroscopy. The particle size was estimated from broadening of XRD peak using Scherrer’s formula and also from effective band gap by absorption peak using effective mass approximation model. The size obtained from XRD and absorption peaks are in agreement with each other. It is observed that the samples consist of separated, well-defined spherical particles and show a small size distribution as well as a characteristic blue shift due to quantum confinement in their optical absorption as well as PL spectra. It is found that the size of CdSe nanoparticles decreases, as the concentration of capping agent is increased. The intensity of PL peak increases and the peak shift towards blue region as the particle size is reduced. The sharp PL spectra also indicate that the nanoparticles are monodispersed.