Experimental evidence of the Coulomb interaction effects in CdS1-xSex quantum dots

Photoacoustic and photoluminescence studies on CdS1-xSex nanocrystals grown in a transparent borosilicate glass matrix are reported. Our analysis points out the important role played by the Coulomb interaction in quantum dots whose radii range around the exciton Bohr radius: (1) strong polar coupling to the lattice; (2) observation of optical transitions with different radial quantum numbers in photoacoustic spectra. Photoacoustic spectroscopy has allowed the direct observation of several low and high index states. The experimental results have been shown to be in good agreement with the effective mass- approximation calculations in which the strain effects, due to the hydrostatic compression of the glass matrix on semiconductor nanocrystals, and size dependent dielectric constant have been taken into account.