Photoinduced photoluminescence variations of CdSe quantum dots in polymer solutions

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 similar to 7 to similar 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.