Ultrafast Excitation Energy Transfer in Vinylpyridine Terminated Silicon Quantum Dots

Water-soluble 2- and 4-vinylpyridine terminated silicon quantum dots (SiQDs) with sizes between 2 and 3 nm were obtained by HF etching of oxidized SiQDs and subsequently passivating with vinylpyridine ligands via thermal hydrosilylation. The functionalized SiQDs emit photoluminescence in the blue-green spectrum with quantum yields around 30%. The photoluminescence is ascribed to radiative recombination of excitons confined to the SiQD core. Indication of efficient electronic interactions between excited ligand states and SiQD conduction band states has been achieved by real-time monitoring excitation relaxation dynamics on the subpicosecond time scale using time-resolved laser spectroscopy techniques. The observed ultrafast excitation relaxation dynamics involving decay and rise dynamics faster than 1 ps were ascribed to electronic excitation energy transfer from an initially photoexcited ligand state to SiQD conduction band states. These results were analyzed by performing a state population analysis on the basis of electron exchange interactions.