Nanocrystalline CdSe formation by direct reaction between Cd ions and selenosulfate solution

We investigate the reaction between selenosulfate and (noncomplexed) Cd ions in aqueous solution to form CdSe. The resulting precipitate, which is initially white (mainly CdSO3) turns yellow and finally orange. The initial precipitate is CdSO3, which gradually reacts with selenosulfate to give CdSe. The CdSe forms as a disordered phase surrounding the CdSO3, and this largely amorphous CdSe breaks off from the CdSO3 crystals to form nanocrystals of CdSe. The color changes during the reaction, due to size quantization of the CdSe nanocrystals, were correlated with the measured CdSe crystal sizes.