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].