Figure 1

(Color online) HRTEM images revealing (top) three layers of SiNCs, marked by dashed white lines, embedded in the amorphous phase of ${\text{SiO}}_2$. The SiNCs are marked by circles. The insets A, B, C, D, E and F are few representative images of the silicon crystal planes, obtained by filtering the corresponding images of the nanocrystals in the frequency domain. (bottom) The same for a crystalline silicon nanorod coated by amorphous ${\text{SiO}}_2$ with the inset showing the crystal planes of the nanorod after filtering.Reuse & Permissions

Figure 2

(Color online) Room-temperature photoluminescence spectra from (a) SiNRs after different times of oxidation and (b) superlattices of SiNCs with different diameters. The insets show the models for SiNRs and SiNCs used to derive the symmetries of the structures.Reuse & Permissions

Figure 3

(Color online) The measured PL lifetime (symbols) versus the inverse temperature for (a) SiNRs after 180 min of oxidation at several photon energies. The solid lines represent the best fit the data to the three-level model of Eq. (1). The inset is a simple scheme of the four excitonic levels (plus the ground state of no excitons) and the allowed optical transitions. (b) The PL lifetime for SiNCs with average diameter of 2.3 nm at photon energy of 1.72 eV. The black solid line represents the best fit of the data to a three-level model while the red line represents the best fit to a two-level model. In both figures, the red dashed areas represent the range of low temperatures where the PL is quenched.Reuse & Permissions

Figure 4

(Color online) Schematic illustration of the excitonic fine structure for (a) SiNCs and (b) SiNRs oriented along the $⟨111⟩$ direction. From left to right we present the excitonic levels neglecting both the direct and the exchange interactions $\left(T_2\times T_2\right)$, splitting due to direct interaction $⟨J⟩$ and finally, the excitonic pattern after introducing the exchange interaction, $⟨K⟩$. For comparison, the measured energies and lifetimes of the upper three excitonic states are presented. The corresponding spin and orbital selection rules for each level are presented in the table on the right sides. The level's notations are explained in the text. The vertical dashed arrows indicate the measured splitting due to exchange interaction (blue) and due to direct interaction (black).Reuse & Permissions