Hot-carrier-mediated impact excitation of Er³⁺ ions in SiO₂ sensitized by Si Nanocrystals

Past research has shown that indirect excitation of Er³⁺ ions in SiO₂ solid-state matrix with Si nanocrystals can be achieved by different pathways. Here, we investigate the impact excitation mechanisms in detail by means of time-resolved photoluminescence spectroscopy. We explicitly demonstrate that the free carrier impact excitation mechanism is activated as soon as the carriers obtain sufficient excess energy. The “hot” carriers with the above-threshold energy can be created upon optical pumping in two ways: either upon absorption of (i) a single photon with an energy exceeding a certain threshold hν > Eth or (ii) following absorption of multiple photons of lower energy in a single nanocrystal, hν < Eth, followed by an Auger recombination of the generated multiple e-h pairs. In addition, we show that the impact excitation dynamics by hot carriers are similar, regardless of the mode in which they have been created.