Influence of thermal annealing on the structural and optical properties of CdSe nanoparticles

CdSe nanocrystals of ∼3–4 nm size have been synthesized by hot-injection method. The influence of thermal annealing in air- or N2-atmosphere on the morphology and optoelectronic properties of synthesized CdSe nanoparticles has been elucidated. The CdSe nanoparticles showed phase transformation upon annealing in air at 350 °C from nanocrystalline sphalerite cubic (Zinc Blende, β-CdSe) structure to hexagonal (Wurtzite, α-CdSe) structure with a binding energy (Cd 3d5/2 peak) shift of 0.70 eV. Remarkable differences in the morphology and optoelectronic properties between air- and N2- annealed CdSe nanoparticles were clearly observed. The intensity of PL emission increased substantially after annealing in air or N2-atmosphere at 250 and 350 °C, respectively, indicating the improvement of crystallinity and surface passivation characteristics of the CdSe nanocrystals.