Visible photoluminescence bands at about 2eV were studied in O-deficient amorphous material which had been 60Co -irradiated to doses of less then 1MGy, and excited by 2 to 4eV photons. In addition to the well-known 1.9eV photoluminescence band that was due to non-bridging O hole centers, another photoluminescence band was observed at 2.2eV when the material was excited using 3.8eV photons. The intensity of the 2.2eV band increased with decreasing O partial pressure during sample preparation. Electron spin resonance measurements showed that the intensity of the 2.2eV band was related to the concentration of the E’ center; a paramagnetic state of a cluster of Si atoms. After much greater -irradiation, to doses of up to 10MGy, a new photoluminescence band was introduced at 1.75eV under excitation by 2.5eV photons; together with the 1.9 and 2.2eV photoluminescence bands. Upon comparing its spectral shape and excitation energy with a known photoluminescence band in Si-implanted amorphous SiO2, it was suggested that the 1.75eV band was associated with Si nano-crystals that formed from Si clusters.

H.Nishikawa, E.Watanabe, D.Ito, Y.Sakurai, K.Nagasawa, Y.Ohki: Journal of Applied Physics, 1996, 80[6], 3513-7