ABSORPTION PROPERTIES OF CDS NANOCRYSTALS IN GLASSES - EVIDENCE OF BOTH WEAK AND STRONG CONFINEMENT REGIMES

Experimental evidence of both weak and strong confinement regimes is reported on CdS nanocrystals embedded in glass matrix. Classic methods for nanocrystallite preparation meet a principal difficulty, the polydispersion in size of crystallites due to several difficulties such as coalescence and decomposition of particles with time and high temperatures. In this work, we used a new route to elaborate CdS-doped sodium borosilicate glass from gel formed in an aqueous medium. Our vitreous matrix is fully and swiftly densified at relatively low temperature, providing us with CdS nanocrystallites yielding fine band-edge structure and small size dispersion. Low temperature absorption spectra have been interpreted in terms of excitons and electron-hole confinements, taking account of both a Lorentzian broadening of the energy states inside each nanocrystal and a Gaussian size-distribution. It has been shown that, for very small crystallites, the strong blue-shift of the absorption edge due to the quantum size effects, is partially compensated by a red-shift associated to the size distribution.