Synthesis and luminescence of silicon remnants formed by truncated glassmelt-particle reaction

We have obtained nanometer sized silicon remnants sequestered in glass matrices by terminating the reaction of pure silicon powders dispersed in the viscous melt at a temperature of 1400°C. Repeated use of this truncated melt-particle reaction process dilutes the amount and size of silicon remnants, and bulk samples containing nanosize silicon crystallites embedded in a glass matrix were eventually obtained. These quantum dot sized silicon-in-glass materials emit greenish luminescence with peak wavelengths from ≊480 to 530 nm, considerably shorter than the reddish luminescence (at about 700-850 nm) observed in porous silicon structures prepared by electrochemical etching techniques; upon complete digestion of Si particles by the melt, the luminescence peaks disappear. Since our silicon-in-glass preparation method does not involve etching, the origin of the luminescence is not likely to be due to Si-O-H compounds (e.g., siloxene) postulated recently. The location of the luminescence peaks and the observed silicon crystallite size suggest quantum confinement leading to a widened silicon band gap arising from remnants in the glass matrix smaller than the exciton diameter of bulk silicon (10 nm).