Facile Size Tunable Green Synthesis of Highly Fluorescent Isotropic and Anisotropic CdSe Nanostructures via a Non-phosphine Based Route

We herein report a phosphine-free synthesis of high quality isotropic and anisotropic CdSe nanostructures (NSs) using oleic acid as capping agent and paraffin as the reaction solvent. The effect of Cd:Se ratio and concentration on the optical and structural properties were investigated by UV–Vis absorption and photoluminescence (PL) spectroscopy and high resolution transmission electron microscopy (HRTEM). The optical analysis revealed a red shift in the absorption band and decrease in the Stoke shift as the reaction time and Cd:Se mole ratio increased. The PL quantum yield of the CdSe NSs at higher cadmium precursor concentration (87%) was higher than that obtained at lower precursor concentration (55%). HRTEM analysis showed that small, spherical and mono-dispersed isotropic quantum dots were produced at lower cadmium concentration and at lower Cd:Se ratio while nanorods were produced at higher Cd:Se ratio. At higher precursor concentration and 1:1 Cd:Se ratio, spherical particles were produced at the beginning of the reaction followed by mixtures of spherical and anisotropic structures—rod, triangular, hexagonal and pentagonal nanostructures. Increasing the Cd:Se ratio to 2:1 at higher cadmium concentration resulted in the formation of spherical particles. This synthetic method is simple, rapid, reproducible, cost effective and environmentally benign.