ABSTRACT
The electronic and optical properties of silicon nanostructures
are of fundamental importance for many prospective applications,
including photovoltaic devices, fluorescence labeling of live cells
and targeted drug delivery, light sources for silicon photonics, and
silicon nanocrystal (SiNC)-based memories. More than two-decade
worldwide research in this field has established a global scheme of
electronic excitation decay in luminescent SiNCs: Upon creating an
electron-hole (e/h) pair, no matter whether optically or via electric
injection, energy relaxation of both free electrons and holes sets in,
followed usually by localizing of the photocarriers in surface-related
states. Radiative recombination of these trapped electrons and holes
results in long-lived orange-red luminescence radiation, frequently
denoted as the S(low)-band or sometimes also “the excitonic band.”
The observed long luminescence decay time (of the order of 10-
100 μs) reflects the indirect-band-gap-nature of SiNCs, inherited
from bulk silicon. In some SiNCs, in addition to the S-band, another
luminescence band appears (on the blue wing of the visible region)
featuring much faster decay, the so-called F(ast)-band. The F-band
is frequently observed in SiNCs derived from porous silicon [1],
sometimes in certain chemically synthesized SiNCs [2], and it is
reported rather exceptionally also in SiNCs embedded in a SiO2
matrix [3].
