Such processes still have not been widely investigated. Furthermore, even today, the detailed excitation mechanism of Er3+ ions in SRSO is still not well understood. Investigations of time-resolved photoluminescence of Er3+ ions in SRSO reveal two major excitation mechanisms leading to 1.5-μm emission, distinguishable by their dynamics: a fast relaxation within the Si-NCs and energy transfer to ions (<100 ns), taking Er3+ ions directly to the first excited state, and a slow relaxation and energy transfer, exciting Er3+ ions to higher states. In both cases, however, the emission decay should be slowed down due to slow radiative relaxation from 4 I 13/2 to 4 I 15/2 on a millisecond-microsecond

time scale this website [18–20]. The fast energy transfer has already been related to Auger-type excitation of Er3+ ions directly from the Si-NCs to 4 I 13/2 level of Er3+ ions. In this case, excited ions should be inside the core of Si-NCs or at their surface due to the short range of Auger-type interactions. This mechanism can also be discussed since to obtain a high efficiency of Auger recombination within the Si-NCs, the energy levels of Si-NCs should be well separated from each other to minimize thermal relaxation which strongly

reduces the Auger-type relaxation. It has been shown, however, theoretically that for Si-NCs, especially when surface/matrix interface is included into the calculations, the energy spectrum of Si-NCs is almost continuous above the main absorption edge [21, 22]. Besides, it has been shown recently that in the spectral range of

selleck compound Er3+ Casein kinase 1 emission, another emission with nanosecond decay appears which, however, cannot be related to Er3+ ions. This emission can be assigned more likely to defect states in the SRSO film. Thus, many open questions regarding the origin of the fast process still remain. It is widely believed that the slow process is due to dipole-dipole energy transfer either from the exciton confined inside the Si-NCs or localized at their surface states. In this case, the transfer can occur efficiently (with a rate of 109 s-1) to the ions located even 6 to 7 nm from the Si-NCs, as has been shown by Choy et al. [23]. On the contrary, other authors have proposed that the optimal distance between Si-NCs and Er3+ ions is on the order of 0.5 nm only [24, 25]. With such a short interaction distance, the question regarding the nature of energy transfer and validity of dipole-dipole interaction only became important. Moreover, in case of slow energy transfer, the intermediate defect states in the SRSO matrix became important and can also participate in Er3+ excitation allowing exciton migration before the exciton transfers its energy to Er3+ ions. This should also increase the distance of Si-NC-Er3+ interaction.