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Preparation and spectroscopic investigation of CdS/CdSe/CdS quantum-dot quantum-well heterostructures.

CdS/CdSe/CdS quantum-dot quantum-well heterostructures with the different thicknesses of CdSe well layers were synthesized by using the colloidal chemical method. The absorption, photoluminescence and Raman scattering spectra of CdS cores, and CdS/CdSe, CdS/CdSe/CdS structures were investigated. A comparative study of their optical properties confirmed the formation of CdSe well and exterior CdS shell. Raman spectra of the nanostructures exhibit the quantum confinement of the optical phonons and the appearance of the surface phonons. It was found that the temperature dependence of the photoluminescence emission energy is described by Varshni relation with the different temperature coefficients for CdS/CdSe and CdS/CdSe/CdS structures. Upconversion luminescence was observed at low temperatures. The optical and vibrational properties of quantum-dot quantum-well heterostructures have been discussed.