Charge-Transfer-Induced Photoluminescence Enhancement in Colloidal Silicon Quantum Dots

Abstract

Charge transfer interaction between colloidal silicon (Si) quantum dots (QDs) and adsorbed molecules was investigated by means of photoluminescence (PL) spectroscopy. The molecule employed is tetrathiafulvalene (TTF), which has the highest occupied molecular orbital (HOMO) near that of Si QDs and can act as an electron donor to Si QDs. The energy difference between the HOMOs of TTF and Si QDs was controlled by changing the size of Si QDs. We found that the PL of Si QDs is strongly modified by the adsorption of TTF and that the PL change is reversible, that is, removal of TTF from a colloidal solution recovers the PL intensity. In the smallest Si QDs, where the HOMO level is expected to be 0.11 eV lower than that of TTF, a 2.5-fold enhancement of the PL was observed. The PL enhancement suggests that Si QDs having p-type behavior are compensated by electron transfer from TTF, similarly to the case of substitutional phosphorus doping in Si QDs. The observed size dependence of the PL enhancement factors sugge...