Manifestations of three-dimensional confinement effects in the optical spectra of CdSe quantum dots in thin film form

Abstract

The manifestations of three-dimensional quantum size effects in the optical spectra of chemically deposited cadmium selenide quantum dots (in thin film form) are investigated, including the influence of the coalescence process and the crystal growth on these effects. The experimentally obtained blue shift of the band-gap energy for as-deposited CdSe quantum dot thin films (using chemical bath deposition) is 0.34 eV with respect to the corresponding value for microcrystalline (bulk) material. Upon thermal treatments, the absorption edge of CdSe thin films is red shifted (in comparison with the absorption edge of as-deposited ones) and band-gap energy tends to approach the bulk value. This finding is attributed to the increase of electronic contact between nanocrystals and irreversible disappearing of the confinement effects. The experimental blue shifts of the band-gap energies of as-deposited and annealed CdSe thin films (with respect to the corresponding bulk value) were compared with the theoretical ones, predicted according to the Brus model.