Measurement of the photostability of silicon nanoparticles under UVA and near infrared irradiation

We examine the photostability of silicon nanoparticles when they are dispersed in liquid or immobilized in gels or on surfaces. We show that the photoluminescence in static solution develops, under UV irradiation, a long-term stability at the 50% level. Under the same conditions, common dye molecules such as coumarin and stilbene quench with time at rates 8 and 50 fold faster, and exhibit no long-term stability. For the case of immobilized particles in agarose gel as well as on a quartz substrate we used two-photon near infrared femtosecond excitation at 780 nm to induce the blue luminescence. ''Parking'' the excitation beam, focused on such stationery particles shows that they, unlike similarly immobilized dye molecules, are highly photostable at more than 80%-90% level and do not bleach. The photostability is discussed in terms of excited state interactions and structuring of the silicon outer shell.