We present results on the photoluminescence (PL) properties of silicon nanocrystals as a function of their size. The nanocrystals are synthesized by laser pyrolysis of silane in a gas flow reactor and deposited at low energy on a substrate after a mechanical velocity and size selection. Both the photoluminescence spectroscopy and yield have been studied as well as the effect of aging of the samples in air. The measurements show that the PL of the silicon nanocrystallites follows the quantum confinement model very closely. The apparent PL yields are rather high (up to 18%). From evaluation of the size distribution obtained by atomic force microscopy it is concluded that the intrinsic PL yield of the nanocrystals can reach almost 100%. These results enabled us to develop a simple theoretical model to describe the PL of silicon nanocrystals. This model can also explain the changes of PL with aging of the sample, just by invoking a decrease of the size of the crystalline core as a result of oxidation.

Silicon nanocrystals with diameters between 2.5 and 8 nm were prepared by pulsed ${\mathrm{CO}}_2$ laser pyrolysis of silane in a gas flow reactor and expanded through a conical nozzle into a high vacuum. Using a fast-spinning molecular-beam chopper, they were size-selectively deposited on dedicated quartz substrates. Finally, the photoluminescence of the silicon nanocrystals and their yield were measured as a function of their size. It was found that the photoluminescence follows very closely the quantum-confinement model. The yield shows a pronounced maximum for sizes between 3 and 4 nm.

This work examines the initial growth and collapse stages of bubbles induced by laser ablation in liquids. First, the bubble shape and size are tracked using an ultrafast camera in a shadowgraph imaging setup. The use of an ultrafast camera ensures a high control of the reproducibility, because a thorough measurement of each bubble lifetime is performed. Next, an analytical cavitation-based model is developed to assess the thermodynamic bubble properties. This study demonstrates that the bubble evolution is adiabatic and driven by inertial forces. Surprisingly, it is found that the bubbles consist of significantly more solvent molecules than ablated matter. These results are valuable to the field of nanoparticle synthesis as they provide insight into the mechanics of laser ablation in liquids.