Structural characterization of chemically synthesized CdSe nanoparticles

CdSe nanoparticles were prepared at room-temperature via direct reaction between Cd(NO3)2 and Na2Se in the presence of cetyltrimethyl ammonium bromide (CTAB) used as a capping material. The nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-Visible absorption spectrum, Fourier transform infrared (FT-IR) spectroscopy, Raman scattering, differential scanning calorimetry (DSC), differential thermal gravimetric (DTG) and heat stage X-ray diffraction (HS-XRD).Analysis of the obtained data reveals the precipitation of defective zinc blende CdSe nanoparticles of size about 11 nm in diameter. A blue shift in the optical gap, from 1.71 to 1.82 eV, has been observed for the absorption spectrum of the synthesized CdSe nanoparticles, as an indication of quantum confinement effect. The zinc blende phase is enhanced upon annealing above the melting of Se (220 °C) as is transformed into a better order and stable wurtzite structure upon further heating. More than one melting point has been recorded for the CdSe nanoparticles referring to different ranges of particle sizes (7:25 nm). A value of 810 °C characterizes the melting point of the predominant size (11 nm) of the CdSe nanoparticles.