Effect of oxygen and polymer matrix on photo-induced changes in CdSe quantum dots

Abstract

When quantum dots (QDs) are irradiated with light, they are subject to photoinduced phenomena, such as photooxidation, photoluminescence (PL) blue-shift, photodarkening (PD) and photobrightening (PB). Some applications of QDs require their dispersion in a polymer matrix. In the present work, the type of polymeric matrix and surrounding gas were investigated as interdependent factors that induce blue shift, PD, and PB of CdSe QDs. CdSe QDs were dispersed in films of polystyrene (PS) and poly (methylmethacrylate) (PMMA). The films were purged with Ar and O2 gases for 8 h and then continuously irradiated with a 0.115 W visible laser while collecting PL spectra at time intervals. PD was obvious in PS, while in PMMA, significant PB was observed with no sign of PD. Irradiation under O2 led to a pronounced blue shift, but this was not observed under Ar. In summary, these polymers either protected against or contributed to photochemical alteration of the QDs in very different ways. PS/O2 is a suitable combination for illumination-based applications/studies that require conservation of PL intensity, but not wavelength. On the other hand, PMMA/Ar is suitable for those that require high PL intensity and conservation of PL wavelength. The changes are explained on the basis of the tendencies of molecular oxygen and the PMMA ester group to oxidize or passivate the QDs, while PS and Ar act as spectators.