Photoluminescence Quenching and Intensity Fluctuations of CdSe−ZnS Quantum Dots on an Ag Nanoparticle Film

Abstract

Intermittent “on” and “off” (blinking) photoluminescence (PL) of single-CdSe/ZnS quantum dots (QDs) is modified when placed on an Ag nanoparticle (NP) film into stochastic fluctuations with nonzero intensity “off” (pseudo off) periods. Also, the PL quantum efficiency (from 0.42 to 0.22) and lifetime (from 5.2 to 1.5 ns) of QDs are considerably decreased at ensemble level in the presence of Ag NPs, and a histogram of the PL lifetime of single-QDs is shifted (from 4.2 to 1.7 ns) and tapered (full width at half-maximum from 3.3 to 1.1 ns) when placed on an Ag NP film. The quenching of the PL quantum efficiency and decrease of the PL lifetime are attributed to ultrafast energy transfer from photoexcited QDs to Ag NPs. The energy-transfer process competes with exciton relaxations and influences carrier trapping in surface defect-states (band gap defects) and Auger relaxation, which are considered to be the origins of blinking. The contribution of surface-states on the modified PL was identified from decreased ...