Size effects on optical transition energies in CdS_xSe_1−x semiconductor nanocrystal glass composites

We report results of measurements of optical transition energies in CdSx Se1−x nanocrystals embedded in a glass matrix. By varying annealing temperature and growth time, we obtained a series of samples with crystallite sizes from 1.8 to 12.4 nm in diameter. We carried out Raman experiments and transmission electron microscopy to determine the composition and the crystallite diameter, respectively, of the semiconductor particles. We measured absorption and electromodulation spectra to identify the quantized energy levels. Two electromodulation peaks that are due to the valence band and the split-off valence band are clearly resolved. The shape of the electromodulation spectrum is significantly affected by the heavy-hole and light-hole splitting. An analysis of the change in optical transition energies with particle size shows that it is necessary to consider the effect of finite well depth of only 1–2 eV for the conduction band.