Impact of photo-irradiation on the optical and spin properties of chiral CdS quantum dot films

Chiral quantum dots (QDs) are expected to play a significant role in chiral molecular recognition, spin-selective filtering for charge transport, and various other fields. Photo-irradiation can enhance the photoluminescence (PL) of chiral CdSe QD films, which serves as a convenient method to modulate the optical properties. However, the effects of photo-irradiation on the absorption and spin properties of chiral QDs remain unclear. In this study, we investigate the influence of photo-irradiation on the PL, absorption, and spin properties of chiral L/D-cysteine-capped CdS QD films. Under the irradiation of the 458 nm continuous wave laser, the PL intensity of chiral CdS QD films can be significantly enhanced by over 50 times and the absorption peak exhibits a blue shift of approximately 3 nm. The transient transmission dynamics before and after irradiation indicate that the bleach recovery lifetime became longer after irradiation, which can be attributed to the increase in radiative recombination. Furthermore, the strength of the electron spin is diminished due to a decrease in the number of charge-separated electrons. The significant enhancement in PL intensity, coupled with the increased radiative recombination and the reduction in spin signals, strongly suggests that surface defects are effectively passivated. The influence of photo-irradiation on the optical properties of chiral QDs provides valuable insights for the design of chiral nanomaterials and their applications.