Photoluminescence and XPS investigations of Cu^2R-doped ZnS quantum dots capped with polyvinylpyrrolidone

Cu²⁺-doped ZnS quantum dots were synthesized by a chemical precipitation method in water/ethanol solution. The quantum dots obtained were characterized by X-ray diffraction, trans- mission electron microscopy and spectroscopy techniques including X-ray photoelectron spectroscopy. The [S^2-]/[Zn²⁺] ratios have an effect on the photoluminescence of both aqueous solutions and powders of Cu²⁺-doped ZnS quantum dots. For aqueous samples, a green luminescence centre is observed in the spectrum of sample 1 with [S^2-]/[Zn²⁺] = 1:2 and a blue one for sample 2 with [S^2-]/[Zn²⁺] = 1:1. For powders, only the green emission is the main luminescence centre, and the integrated intensity in the blue emission region of sample 1 is stronger than that of sample 2. Compared with the spectrum of CuS powders, the X-ray-induced Auger electron spectrum of Cu L₃M₄₅M₄₅ in ZnS quantum dots shows a unique spectral characteristic. The 3d level of the Cu²⁺ ion is split into two different energy levels at 334.0 and 347.2 eV, respectively.