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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 °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).
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