The effect of annealing and photoactivation on the optical transitions of band-band and surface trap states of colloidal quantum dots in PMMA

For optoelectronic applications, colloidal CdSe quantum dots (QDs) have been integrated into solid devices by using optically transparent polymer matrices that embedded the colloidal QDs. We systematically studied the effect of annealing and photoactivation on the band-band (BB) and surface trap state (STS) transitions of colloidal CdSe QDs embedded in polymethylmethacrylate (QDs-PMMA). The QDs-PMMA composites demonstrate enhancement of the STS emissions while their annealing leads to an intensity quench of both BB and STS emissions. The annealing process also causes the red shift of the BB emission. By contrast, photoactivation of QDs-PMMA composites results in the remarkable recovery of luminescence intensity accompanied by blue shift of the emissions. Furthermore, it is found in the photoactivation process that the STS emission can be saturated earlier than the BB emission, which renders it possible to tune the light color of the emissions. The combination of annealing and photoactivation could undoubtedly provide an effective way to precisely tune the colors of light-emitting devices that use colloidal CdSe QDs.