Photostability of CdSe Quantum Dots Under Visible Light Irradiation: Effects of Surface Ligands, Solvents, and BHT Antioxidant

Abstract

Photostability is a key parameter determining the long-term stability of quantum dots (QDs), thus rendering it imperative to investigate the intrinsic structural and extrinsic environmental factors that affect their photostability. Herein, we systematically investigated the stability of CdSe QDs capped with stearic acid (SA) and tributylphosphane (TBP) in n-hexane and toluene, as well as that of CdSe QDs capped with 3-mercaptopropionic acid (MPA) in water and ethanol, under Xe lamp irradiation. CdSe QDs capped with different ligands exhibited similar particle sizes (ca. 3.3 nm), maximum absorption wavelengths (560–568 nm), and emission wavelengths (570–576 nm). CdSe-SA QDs exhibited the highest photostability, followed by CdSe-TBP QDs, while CdSe-MPA QDs showed the poorest stability. Regarding solvent effects, oil-soluble CdSe-SA QDs and CdSe-TBP QDs showed better stability in n-hexane than in toluene; water-soluble CdSe-MPA QDs were more stable in water than in ethanol. Moreover, the SA ligand was found to be more effective than TBP and MPA in enhancing the fluorescence quantum yield (FQY) and lifetime of CdSe QDs. Through electron paramagnetic resonance (EPR) spectroscopy and chemical probe experiments, it was revealed that photo-generated singlet oxygen (¹O₂) acts as the predominant reactive oxygen species (ROS) responsible for the photocorrosion of CdSe QDs, and its yield was well correlated with the corrosion rates of the QDs across the different ligand-solvent combinations. Additionally, the antioxidant 2,6-ditertbutyl-4-methylphenol (BHT) was found to effectively improve the photostability of CdSe QDs capped with the three types of ligands. This study reveals the synergistic roles of ligands, solvents, and additives in determining the photostability of CdSe QDs, providing key insights for the design of high-performance and long-lasting devices based on QDs.