Photoluminescence (PL) quantum efficiencies and lifetimes of CdSe quantum dots (QDs) were investigated under photoactivation in different chemical environments including polymer solutions and solvent systems. We observed considerable enhancement of the PL quantum efficiency of the QDs when photoactivated above the band gap in the presence of polymers such as poly(dimethyl siloxane) (PDMS), poly(vinyl pyrrolidone) (PVP), and poly(butadiene) (PBD). Furthermore, the PL spectra and the enhanced PL quantum efficiencies of the QDs were considerably stabilized under continuous photoactivation in the presence of dissolved polymers. Under photoactivation, the PL quantum efficiency was increased from 8% to 26−37% depending on the polymer environment. An increase of the PL quantum efficiency was also observed in solvents such as CHCl3 and n-butanol. However, photoactivation of the QDs in solvents with small dipole moments such as n-hexane and toluene resulted in substantial decreases of the PL quantum efficiency (from 8% to <1%). The photoactivated PL intensity of the QDs was stable in the presence of polymers as a result of static passivation of QDs' surface. In general, the increase of the PL quantum efficiency of the QDs under photoactivation was associated with an increase of the average PL lifetime values (from ∼7 to ∼12 ns). On the other hand, the increase of the PL quantum efficiency (from 8% to 37%) of QDs in the presence of PVP was associated with a decrease of the average PL lifetime value (from 7.16 to 3.51 ns). From the PL variations of the CdSe QDs under continuous photoactivation in the presence of different polymers and solvents, we determined that static passivation of the surface defects by molecules in the environment plays an important role in the surface-related emission and stability of the photophysical properties of the QDs. The variations of the PL lifetimes and quantum efficiencies under different chemical environments were helpful not only in understanding the involvement of surface states in the deactivation processes of photoexcited QDs but also in identifying ideal polymers and solvents for photoinduced surface passivation of QDs.

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 energytransfer 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 contribution of a slow component to the PL decays of ensemble-and single-QDs in the presence of Ag NPs. On the basis of ensemble averaged PL intensity and lifetime and single-QD lifetime and intensity trajectory analyses, we propose that the energytransfer process from photoexcited QDs to Ag NPs result a redistribution of relaxation processes and provide fluctuating trajectories with nonzero intensities to single-QDs. Apart from the observations of modified blinking and narrow lifetime distribution of QDs, the current work partially supports a model proposed by Markus and co-workers that blinking is related to localization of charge carriers in defects.