Redox-assisted Asymmetric Ostwald Ripening of CdSe Dots to Rods

The redox-assisted asymmetric Ostwald ripening of dots to rods was observed upon annealing a concentrated dispersion of CdSe nanocrystals (NCs) containing 0.1 M CdCl2 in 3-amino-1-propanol (APOL)/H2O (v/v = 9/1) at 135 degrees C. Transmission electron microscopic investigation, along with UV-vis and photoluminescence results, revealed that, while the length of these NCs increased upon annealing, their diameter remained constant. The surface oxidation of NC Se atoms to SeO2 and its subsequent dissolution into the basic APOL/H2O mixture as SeO32- was found instrumental for such dot-to-rod transformation. The amine-assisted SeO2 reduction to Se0 (as confirmed by X-ray photoelectron spectroscopy and X-ray diffraction results) provides the Se source for further NC growth. The preferential growth along the c-axis leads to the formation of rods with zinc blende CdSe structure at its growing ends, due to the low-temperature growth conditions.