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 r eported on CdS nanocrystals embedded in glass matrix. Classic methods for nanocrystallite preparation meet a principal difficulty, the polyd ispersion in size of crystallites due to several difficulties such as coalescence and decomposition of particles with time and high temperat ures. 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, p roviding us with CdS nanocrystallites yielding fine band-edge structur e and small size dispersion. Low temperature absorption spectra have b een interpreted in terms of excitons and electron-hole confinements, t aking account of both a Lorentzian broadening of the energy states ins ide each nanocrystal and a Gaussian size-distribution. It has been sho wn that, for very small crystallites, the strong blue-shift of the abs orption edge due to the quantum size effects, is partially compensated by a red-shift associated to the size distribution.