Electrochemical synthesis and optical properties of ultra-fine CdSe nanoparticles

Colloidal solutions (~0.3 mol/L) of CdSe nanoparticles in xylene have been synthesized by the electrochemical method from an acid electrolyte based on HNO3 + HCl (2:1) mixture using extraction into xylene. It has been found that CdSe nanoparticles of small size (2–5 nm) synthesized on the cathode are readily extractable in xylene, whereas nanoparticles of larger size (20–100 nm) remain in the aqueous electrolyte and dissolve in the nitric–hydrochloric acids mixture. An X-ray phase analysis of powders of 2–5 nm CdSe nanoparticles showed them have a mixed cubic/hexagonal crystal structure. It has been found from measurements of absorption and photoluminescence spectra that the CdSe nanoparticles of this structure have a broad photoluminescence band (λ max = 500 nm) at a narrow absorption peak (λ max = 420 nm), which may be due to stacking fault formation in nanoparticles of mixed cubic/hexagonal structure. Using this electrolyte with a xylene surface layer under continuous electrolysis conditions and extraction of 2–5 nm CdSe nanoparticles with a content of up to 0.05 g in 1 cm3 xylene (~0.3 mol/L) was obtained. Such colloidal solution can be used to obtain optical nanocomposites by incorporation CdSe nanoparticles into a liquid–crystalline cadmium caprylate matrix. The spectral characteristics such of composites have been studied by adsorption spectroscopy and fluorescence.