Sol–gel preparation of Ge nanocrystals embedded in SiO 2 glasses

Abstract

Ge nanocrystals embedded in SiO 2 glasses were prepared by an easy sol–gel method. The gels synthesized through hydrolysis of Si(OC 2H 5) 4 and 3-trichloro-germaniumpropanoic acid (Cl 3–Ge–C 2H 4–COOH) were heated at 600°C for 10 h in air atmosphere to form GeO 2–SiO 2 glasses. The gel-glasses were further heated at 500–700°C in H 2 gas atmosphere, in which Ge 4+ 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.