Abstract
Silicon nanocrystals (Si-nc) embedded in silica exhibit intense visible photoluminescence (PL) at room temperature. However, under continuous wavelength (CW) laser excitation at 405 nm, the Si-nc PL intensity decreases with time, approximately with two decay constants. The fast decay component is unchanged by repetitive laser exposures, it is related to the local sample heating induced by the laser. The slower time constant corresponds to a permanent decrease of the PL emission. This photodeterioration strongly affects the precision of optical gain measurements using VSL (Variable Stripe Length) or P&P (Pump and Probe) techniques, hindering the development of Si-nc technology for photonics applications. In this context, a procedure that would restore the PL intensity of Si-nc samples or minimize this deterioration is highly desirable. UVC light (254 nm) irradiation of samples followed by an annealing at different temperatures for 1 h under nitrogen flux increases the PL emission of Si-nc embedded in silica that have been previously exposed to a CW laser pumping. Although this procedure does not prevent the decrease of the PL intensity associated with the increase of sample temperature under CW pumping (the fast decay component), it contributes significantly to reduce the permanent deterioration of the PL intensity. This procedure can also be applied to non-irradiated samples. The PL emission collected from treated samples was studied as a function of laser irradiation time, and compared to that of non-treated samples. The resistance to degradation of light-emitting silicon nanocrystals can be increased by UVC irradiation followed by annealing at an optimal temperature of 400 degrees C under nitrogen environment. Following this treatment, a reliable optical gain measurement can be performed once the local heating has been stabilized (the fast decay component).