We have investigated visible photoluminescence excited by Ar-ion laser (488 nm, 2.54 eV) at room temperature from Si+-implanted silica glass, as-implanted and after subsequent annealing in vacuum. We found two visible luminescence bands: one peaked around 2.0 eV, observed in as-implanted specimens and annealed completely after heating to about 600 °C, the other peaked around 1.7 eV observed only after heating to about 1100 °C, the temperature at which Si segregates from SiOx. It was found that the 2.0 eV band anneals parallel to the E′ centers, as detected by electron spin resonance studies. It was also found that Raman lines around 520 cm−1, due to Si—Si bonds, grow and that interference patterns are induced by annealing Si+-implanted silica glass. Based on these studies, we ascribe the 2.0 eV band to the electron-hole recombination in Si-rich SiO2 and the 1.7 eV band to the electron-hole recombination in the interface between the Si nanocrystal and the SiO2 formed by segregation of crystalline Si from SiOx.
We develop a model for the excitation of erbium ions in erbium-doped silicon nanocrystals via coupling from confined excitons generated within the silicon nanoclusters. The model provides a phenomenological picture of the exchange mechanism and allows us to evaluate an effective absorption cross section for erbium of up to 7.3ϫ10 Ϫ17 cm 2 : four orders of magnitude higher than in stoichiometric silica. We address the origin of the 1.6 eV emission band associated with the silicon nanoclusters and determine absorption cross sections and excitonic lifetimes for nanoclusters in silica which are of the order of 1.02ϫ10 Ϫ16 cm 2 and 20-100 s, respectively.
A method for the fabrication of luminescent Si nanoclusters in an amorphous SiO2 matrix by ion implantation is reported. We have measured the dose (concentration of excess Si atoms) and annealing time dependence of the photoluminescence of Si nanoclusters in SiO2 layers at room temperature. The samples were fabricated by ion implantation and subsequent annealing. After annealing, a photoluminescence band below 1.7 eV has been observed. The peak energy of the photoluminescence is found to be almost independent of annealing time, while the intensity of the luminescence increases as the annealing time increases. Moreover, we found that the peak energy of the luminescence is strongly affected by the dose of implanted Si ions, especially in the high-dose range. We also show direct evidence of widening of the band-gap energy of Si particles of a few nanometers in size by employing photoacoustic spectroscopy. These results indicate that the photons are absorbed by Si nanoclusters, for which the band-gap energy is modified by the quantum confinement effects, and the emission is not simply due to direct electron–hole recombination inside Si nanoclusters, but is related to defects probably at the interface between the Si nanoclusters and SiO2, for which the energy state is affected by cluster–cluster interactions.
We have investigated visible photoluminescence excited by Ar ion laser (488 nm, 2.54 eV) at room temperature from Si+-implanted thermal oxide films grown on crystalline Si wafer, as-implanted and after subsequent annealing in vacuum. We found two types of visible luminescence bands similar to those of silica glasses; one band is observed in as-implanted specimens and disappears after heating to about 600 °C, and the other band is observed only after heating the specimens to about 1100 °C. Though the shapes of these luminescence spectra are different from those having been observed in Si+-implanted silica glass, the origins of these bands are the same as in silica glass. We discuss the similarities and the differences of luminescence bands in Si+-implanted silica glasses and thermal oxide films grown on crystalline Si.
Silica thin films containing Si nanocrystals and Er3+ were prepared by ion implantation. Excess Si concentrations ranged from 5% to 15%; Er3+ concentration for all samples was 0.5%. Samples exhibited photoluminescence at 742 nm (attributed to Si nanocrystals), 654 nm (defects due to Er3+ implantation), and at 1.53 μm (intra-4f transitions). Photoluminescence intensity at 1.53 μm increased ten times by incorporating Si nanocrystals. Strong, broad photoluminescence at 1.53 μm was observed for λPump away from Er3+ absorption peaks, implying energy transfer from Si nanocrystals. Erbium fluorescence lifetime decreased from 4 ms to 1 ms when excess Si increased from 5% to 15%, suggesting that at high Si content Er3+ ions are primarily situated inside Si nanocrystals.
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