Photo- and electro-luminescence of cadmium selenide nanocrystals and nanocomposites

Nanocrystalline cadmium selenide(CdSe) powder as well as nanocomposites of CdSe in poly vinyl alcohol (PVA) matrix were prepared by chemical method and characterized by TEM and XRD. Hexagonal phase has been observed with size depending on preparation conditions. Absorption spectra of powder samples give a peak and then monotonous increase in absorption at shorter wavelengths where as nanocomposites show only absorption edge. Powder samples were excited by 300 nm UV light and photoluminescence (PL) spectra show single peak between 345 and 400 nm. It is seen that as the particle size is reduced the intensity of luminescence increases. In case of nanocomposites, PL was excited by 475 nm light and emission spectra show two peaks at 525 and 575–585 nm. Electroluminescence (EL) study of CdSe nanopowder and CdSe/PVA nanocomosite show that the emission starts at a threshold voltage and then increases with voltage. Lower threshold and higher brightness have been observed for smaller particles. Current is found to increase linearly with voltage indicating ohmic nature. The EL spectrum of CdSe/PVA nanocomposites shows only one broad peak at 580 nm similar to PL. The relation between brightness and voltage indicates that EL is produced by acceleration–collision mechanism. The investigations have revealed that intensity of photo- as well as electro-luminescence can be increased by reducing the size of CdSe nanocrystals. Nanocrystalline CdSe powder shows better photoluminescence but for electroluminescence nanocomposite is beneficial.