We investigated the effect of a surface defects, such as losing ligands and external charge, on the electronic structure and the energy transfer between methyl passivated silicon quantum dots (QDs). We have simulated different silicon quantum dots that consists of either 29, 35 or 66 silicon atoms as the QD model with a diameter ranging from 1.2 to 1.6 A to perform DFT and linear response TDDFT calculations.  Our calculations show that the surface defects introduce mid-gap states that are weakly optically active resulting in a lowest energy red shifted absorption band. We then have explored the Forster resonance energy transfer (FRET) rates between QDs of different sizes, different surface passivation, and at different distances. Our results show that removal of ligands from the QD surface increases the rate of energy transfer by 100 folds compared to ideal QDs separated by a distance of 1 nm. Also, introducing charge on the QD increases the rate by at least 10 folds. The higher rates of energy transfer between QDs due to surface defects when packed closely facilitate occupation of the mid-gap trap states leaving the room for direct emission from higher-energy bright states. Such ultrafast energy transfer between QDs with imperfect surface might explain the nature of on-time increase in quantum blinking of closely packed Si QDs observed experimentally.

Effect of surface defects on the optical properties of silicon quantum dots

249th National Meeting (2015)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.