Abstract

Since its establishment as a production technology, nanotechnology has revolutionized the everyday life of billions of people worldwide. The main merit of nanotechnology is the miniaturization, which brings many advantages like the possibility to create more compact devices, to achieve better energy usage, and higher surface-to-volume ratio which enhances physicochemical reactivity, to mention a few. All these effects are related to the mere scaling down in the physical dimension. The nanometric length scale, however, also brings out new physical phenomena related to the finite size of the constituents of matter—atoms and electrons. Among these effects, the quantum confinement phenomenon appearing for dimensions smaller than the exciton Bohr radius is one of the most striking since it reveals itself through a drastic change in the optical properties of semiconductor materials. For example, an indirect band gap semiconductor like silicon switches to direct band gap behavior when the physical size is smaller than about 5–10 nm (Barbagiovanni et al. 2014). This transition substantially modifies the optical absorption and emission properties of the silicon nanomaterial compared to the bulk: the absorption edge shifts to the blue region of the optical spectrum, and bright photoluminescence (PL) appears with wavelength in the optical spectrum depending on the actual size of the nanocrystals.