A new addition to the aerogel community: unsupported US aerogels with tunable optical properties

摘要

Aerogels composed of interconnected networks of CdS building blocks have been prepared from controlled aggregation of discrete nanoparticles followed by supercritical fluid extraction. The resultant materials have surface areas up to 242m(2)/g and average pore diameters in the range of 15-25nm. Powder X-ray diffraction indicates that the average crystallite size is on the order of 2nm in 100degreesC heated aerogels, but increases to nearly 16nm upon heating at 500degreesC. This increase in size is accompanied by a phase change from the cubic to the hexagonal structure. The optical bandgap (measured by absorption onset) is also tunable with heat treatment, and was found to range from 2.2-2.8eV. The photoluminescence excitation spectrum (lambda(ex) = 400nm) of a 100degreesC-heated CdS aerogel is similar to that of the nanoparticulate starting materials, exhibiting both a sharp excitonic peak near 450nm corresponding to band edge emission, and a broad feature in the region 500-700nm, attributed to electron-hole recombination at trap states. (C) 2004 Elsevier B.V. All rights reserved.