Sol-gel preparation of Ge nanocrystals embedded in SiO2 glasses

Ge nanocrystals embedded in SiO2 glasses were prepared by an easy sol-gel method. The gels synthesized through hydrolysis of Si(OC(2)Hs)(4) and 3-trichloro-germaniumpropanoic acid (Cl-3-Ge-C2H4-COOH) were heated at 600degreesC for 10h in air atmosphere to form GeO2SiO2 glasses. The gel-glasses were further heated at 500-700degreesC in H-2 gas atmosphere. in which Ge4+ were reduced to precipitate cubic Ge nanocrystals. The size of Ge crystals is estimated to be from 1 to 13 nm according to the XRD and TEM. The optical absorption edge shifts to higher energy with decrease in the content of Ge in the starting materials, and in the heating temperature and time in H-2 gas atmosphere. This phenomenon is interpreted in terms of a quantum confinement effect of electrons and holes in the Ge nanocrystals. (C) 2002 Elsevier Science B.V. All rights reserved.