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Silicon ions were implanted into fused silica substrates at doses of 1 by 1021, 2 by 1021, 5 by 1021, and 1 by 1022 ions/cm3. The implanted substrates were subsequently annealed at 1100 degrees C for one hour in a reducing atmosphere. Optical absorption spectra recorded after the annealing treatment showed absorption onsets at 316, 373, 434 and 493 nm for substrates implanted with 1 by 1021, 2 by 1021, 5 by 1021, and 1 by 1022 ions/cm3 respectively. Static photoluminescence (PL) measurements indicated red emission between 720 and 770 nm with a slightly increasing red shift with ion dose. Time resolved PL at room temperature revealed slow and fast lifetimes which increased with decreasing temperature. TEM studies showed that the particles size increased with increasing ion dose with typical particle sizes ranging between 2 and 5 nm indicating quantum confinement of the exciton which can account for the blue shift in the absorption edge with decreasing ion dose. However, the maxima in the PL spectra for all ion doses are relatively independent of the ion dose and are strongly Stokes shifted from the absorption spectra suggesting that radiative recombination occurs from a common luminescent center, possibly a surface or interfacial state in the SiOx layer surrounding the nanocrystal.
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