Nanosecond Dynamics of the Near-Infrared Photoluminescence of Er-Doped ${\mathrm{SiO}}_2$ Sensitized with Si Nanocrystals

We report on an observation of a fast $1.5\mu \mathrm{m}$ photoluminescence band from ${\mathrm{Er}}^{3+}$ ions embedded in an ${\mathrm{SiO}}_2$ matrix doped with Si nanocrystals, which appears and decays within the first microsecond after the laser excitation pulse. We argue that the fast excitation and quenching are facilitated by Auger processes related to transitions of confined electrons or holes between the space-quantized levels of Si nanocrystals dispersed in ${\mathrm{SiO}}_2$. We show that a great part—about 50%—of all Er dopants is involved in these fast processes and contributes to the submicrosecond emission.

Figure 1

RT PL spectrum of the investigated sample, ${\lambda }_{\mathrm{exc}}=450\mathrm{nm}$. In the inset: flux dependence of the PL intensity at $\lambda =1.5\mu \mathrm{m}$ for nonresonant (${\lambda }_{\mathrm{exc}}=512\mathrm{nm}$, ○) and resonant (${\lambda }_{\mathrm{exc}}=522\mathrm{nm}$, ■) excitation. ☆ represent the difference between the two curves. Right-hand scale has been calibrated using the data obtained for the ${\mathrm{SiO}}_2\mathrm{\text{:}}\mathrm{Er}$ reference sample (▴).

Figure 2

Double-logarithmic representation of the Er-related $1.5\mu \mathrm{m}$ PL decay, showing three different temporal regimes (RT, ${\lambda }_{\mathrm{exc}}=450\mathrm{nm}$). In the inset: RT PL temporal evolution for the first $10\mu \mathrm{s}$ after the excitation pulse, measured at $\lambda =1.5\mu \mathrm{m}$ for ${\mathrm{Er}}^{3+}$ (○) and at $\lambda =860\mathrm{nm}$ for Si-NC’s (■). Stretched exponential decay formula has been used to fit the Si-NC’s decay ($\tau =1.2\mu \mathrm{s}$, $\beta =0.5$) and single exponential rise for ${\mathrm{Er}}^{3+}$ ($\tau =3.5\mu \mathrm{s}$).

Figure 3

Schematic illustration of different excitation mechanisms proposed to be responsible for the “fast”—regime I—, and the slow—regimes II and III—Er PL.