PHOTOLUMINESCENCE FROM MECHANICALLY MILLED SI AND SIO2 POWDERS

The photoluminescence (PL) in as-received and milled Si and SiO2 powde r is reported. The Si and SiO2 powder is characterized by chemical ana lysis, Raman scattering, x-ray photoelectron spectra, infrared absorpt ion, x-ray diffraction, and differential thermal analysis. The results indicate that the Si powder has amorphous Si oxide and suboxide surfa ce layers. The milling of Si powder results in the formation of nanocr ystalline/amorphous Si components. An amorphous SiO2 component is form ed by milling crystalline SiO2. The PL spectra for as-received Si, mil led Si, and SiO2 powder exhibit similar peak shapes, peak maxima, and full width at half maximum values. For both the as-received and the mi lled Si powder, experimental results appear to exclude mechanisms for PL related to an amorphous Si component or Si-H or Si-OH bonds, or the quantum confinement effect. Similarly, for milled SiO2 powder mechani sms for PL do not appear related to Si-H or Si-OH bonds. Instead the g reatly increased intensity of PL for milled SiO2 can be related to bot h the increased volume fraction of the amorphous SiO2 component and th e increased density of defects introduced in the amorphous SiO2 upon m illing. It is suggested that the PL for as-received Si, milling-induce d nanocrystalline/amorphous Si, and milled SiO2 results from defects, such as the nonbridging oxygen hole center, in the amorphous Si suboxi de and/or SiO2 components existing in these powder samples. The PL mea surement for milled SiO2 is dependent on air pressure whereas that for as-received SiO2 is not, suggesting that new emitting centers are for med by milling.