High quantum yield Cu doped CdSe quantum dots

Small sized high quantum yield copper doped CdSe quantum dots (QDs) were prepared by colloidal precipitation method with a high ratio of thiol groups coordinated at the surface of quantum dots. Both of states of Cu oxidation (+1 and +2) were detected for doped quantum dots. The high percentage of +2 oxidation state of Cu ions has been detected in the samples doped with low concentrations, relative to the samples doped with high concentrations of Cu. The optical transition energy of Cu doped CdSe quantum dots decreased relative to undoped dots due to the formation of mid-gap levels. Band edge and surface state emissions have been observed for undoped quantum dots; whereas for Cu doped CdSe, only broad emission band with a large Stokes shift was observed. High quantum yield reaches 63%, as observed for doped structures with low concentrations due to mid-gap level occupying a permanent hole. The quantum dots doped with high concentrations showed a low quantum yield relative to the samples doped with low concentrations. This has resulted due to the competition of hole trapping between Cu¹⁺ state and hole trap species on the surface of quantum confined structures. It was expected to obtain quantum confined structures doped with low concentrations with promising applications in various optoelectronic devices due to high quantum yield and large Stokes shift. (paper)