Multiphoton Emission Enhancement from a Single Colloidal Quantum Dot Using SiO2-Coated Silver Nanoparticles.

The enhancement of multiphoton emission from a single colloidal nanocrystal quantum dot (NQD) interacting with a plasmonic nanostructure was investigated using SiO2-coated silver nanoparticles (Ag/SiO2) as the plasmonic nanostructure. Using Ag/SiO2 with five different SiO2 shell thicknesses, we observed modification of the emission behavior depending on the distance between the NQD and silver nanoparticle (AgNP). The single-photon emission from a single NQD converted to multiphoton emission with a shortening of the emission lifetime as the NQD-AgNP distance decreased, whereas an increase and decrease in the emission intensity were observed. From the distance-dependent results, we concluded that the probability of multiphoton emission was increased by the quenching of the single-exciton state due to energy transfer from the NQD to the AgNP and that the emission intensity was modified by the enhancement of the excitation rate and quenching. These results indicate that the plasmonic nanostructure is very effective in controlling the emission photon statistics, that is, single- and multi-photon emission and the emission intensity from the single NQD, which is difficult to achieve in an NQD alone.