Photoluminescence decay dynamics of silver/porous-silicon nanocomposites formed by metal-assisted etching

We investigate the photoluminescence (PL) properties of silver/porous-silicon (Ag/PSi) nanocomposites prepared by metal-assisted etching in ${\mathrm{Ag}}_2\mathrm{O}/\mathrm{HF}$ solution, on the basis of steady-state and time-resolved PL spectroscopy measurements. The PL intensity and peak position are strongly dependent on the ${\mathrm{Ag}}_2\mathrm{O}$ concentration. Time-resolved PL measurements reveal that the nonradiative rate decreases with an increase in the ${\mathrm{Ag}}_2\mathrm{O}$ concentration for the Ag/PSi nanocomposites. It is found from x-ray photoelectron spectroscopy measurements that the decrease in the nonradiative rate is caused by the formation of ${\mathrm{SiO}}_2$ layers on the PSi surfaces. Further, the number of light-emitting Si nanocrystals in the nanocomposites, which is estimated from the PL decay rate and PL intensity, increases with the ${\mathrm{Ag}}_2\mathrm{O}$ concentration. From the wavelength dependence of the PL decay rate, it is found that the nonradiative rate is considerably dispersive, i.e., the shorter the wavelength, the higher the nonradiative rate.