Photodeterioration of the silicon nanocrystal emission

Photoluminescence (PL) of silicon nanocrystals (Si-nc) is investigated as a function of exposure time for several laser intensities. Both a strong decrease in luminescence and an energy shift are observed during the illumination period. Decay analysis of the PL emission intensity indicates two timescales: a short timescale (<0.5 min), associated with reversible sample heating effects and a longer timescale (>5 min), attributed to an irreversible sample damage caused by the laser excitation. Both sample heating and damage shift the PL emission toward the red. These longer timescale variations can significantly influence the precision of both PL and optical gain measurements performed at average pumping intensities as low as ∼1 W cm-2. The complex evolution of the Si-nc spectra after a long recovery period indicates that the permanent degradation of the PL signal results from the activation of several sample damaging mechanisms, whose possible origins are discussed.