An Effective Oxidation Approach for the Luminescence Enhancement in CdS Quantum Dots by H2O2

Abstract

Photoluminescence enhancement in CdS nanocrystals was observed via the surface oxidation method. The CdS nanocrystals were oxidized by adding controlled amount of H2O2 solution at room temperature. After the surface oxidation, core-shell nanocrystals were formed. From the XRD measurement, the core diameter of oxidized CdS nanocrystals and local strain decreased. The absorbance edge and photoluminescence peak were blue-shifted depending on the diameter of core CdS nanocrystals after the step oxidation process. From the time resolved photoluminescence (TR-PL) measurement, the CdS nanocrystals passivated with oxide layer showed 100 times higher quantum efficiency (20%) than that of as-synthesized sample. The XPS data revealed that the CdS nanocrystals on the change in the surface chemical state from CdS to CdSO4. This oxide layer on the surface of CdS nanocrystals reduced accumulated strains and acted as surface passivation layer to promote radiative recombination. The step oxidation process of CdS nanocrystals was the one of effective methods to control the size of nanocrystals and form core/shell heterostructures, resulting in quantum efficiency.