Microstructures and optical properties of PVA encapsulated cadmium selenide QD synthesized in non-stoichiometric ratio by green chemical route

Abstract

Cadmium Selenide core quantum dots and rods nanoparticles in polyvinyl alcohol matrix were synthesized in a green chemical route using aqueous solutions of cadmium chloride, selenium, sodium sulfite and PVA, in the non-stoichiometric ratio of Cd:Se (1: 1.8, 1:2.00 and 1:2.20) at pH near 9 in the three samples thermalized at 110°C,140°C and 160°C. XRD spectra confirmed mostly zinc blende unit cell with lattice parameters determined by Nelson-Riley plots (0.5840 nm, 0.5910 nm and 0.5914 nm for the three samples), along with some Wurtzite unit cells whose parameters were determined by the Cohen method. The micro-strains and mean particle sizes were determined by Williamson-Hall plots and found to agree with structural analysis. For zinc blende contents, these were −0.03814 for 1.72 nm, −0.03748 for 1.75 nm and −0.01712 for 3.02 nm particles respectively. The surface morphology as observed by SEM exhibited nano-rods, dots and their agglomerations. Absorption bands were found in the ultraviolet region with meagre values in the visible range. Tauc plots were traced to get optical band gaps of 5.08 eV, 4.90 eV and 4.84 eV for the three sizes of nanoparticles reflecting its dependency on particle size, which indicated a blue shift arising out of quantum confinement. Photoluminescence spectra indicated strong emissions in the ultraviolet range (at 255 nm, 295 nm and 350 nm) and multiple bands in the visible region near 555 nm, 650 nm and 825 nm. Such micro-structural and optical properties as these are suited for applications in solar, electric, photo-physical and bio-imaging devices.