Effects of electron tunneling in photophysics of quantum-sized luminescent nanosilicon

The paper deals with the processes of photoburning and dark recovery of the photoluminescence (PL) yield of a “core-shell”-type hybrid nanoparticles Si/SiO _x (npSi/SiO _x ) after exposure to laser light with a wavelength of 405 nm and power density of 0.05–1 W/cm². The PL of npSi/SiO _x occurs after excitation of nanocrystalline Si core and subsequent energy transfer to the luminescent oxygen-deficient centers (ODC) in the SiO _x shell of a nanoparticle. These photoburning effects linearly depend on the power density of the exciting laser light, and the dynamics of the photoburning of PL is significantly non-exponential: the burning rate strongly drops during the exposure. The stop of laser exposure of npSi/SiO _x is accompanied by a slow dark recovery of the quantum efficiency of PL up to its initial level. We have demonstrated the possibility of controlling the photosensibility of npSi/SiO _x through changing the electron affinity of the environment. We have also proposed a physical mechanism that explains the observed photoburning and subsequent dark recovery of npSi/SiO _x PL based on the existence of “traps” for electrons residing in the SiO _x shell, where the electrons come as a result of tunneling from the excited ODC. The limiting time for this process is the lifetime of PL of ODC ranging from 10^?5 to 10^?4 s. The drop of the burning rate during exposure is caused by a strong difference in tunneling probabilities for different pairs of “ODC-trap”. The dark back tunneling of an electron from a trap to the original ODC occurs significantly (7–10 orders of magnitude) slower than the direct tunneling due to higher energy barrier.

Open image in new window

Graphical abstract Dark recovery of photoluminescence efficiency of Si nanoparticles following laser burning in three surrounding media differing in electron affinity