Optical properties and thermal stability of germanium oxide (GeO2) nanocrystals with α-quartz structure

Germanium dioxide (GeO2) crystals were prepared by a chemical precipitation method at a relatively low-temperature (100 °C). The grown crystals were characterized by studying their microstructure, optical properties and thermal stability. The results indicate that the grown GeO2 crystals exhibit α-quartz type crystal structure. The lattice parameters obtained from XRD were a = 4.987(4) Å and c = 5.652(5) Å. Electron microscopy analysis indicates a high structural quality of GeO2 crystals grown using the present approach. Optical absorption measurements indicate a direct bandgap of 5.72 eV without any additional bands arising from localized or defect states. Thermogravimetric measurements indicate the temperature stability of the grown GeO2 nanocrystals. Microscopic analysis coupled with energy dispersive X-ray spectroscopy of the GeO2 crystals with α-quartz type crystal structure indicates their stability in chemical composition up to a temperature of 400 °C. The surface morphology of GeO2 crystals, however, found to be changing with the increase in temperature.