Oxidation-induced quenching mechanism of ultrabright red carbon dots and application in antioxidant RCDs/PVA film

Red emissive carbon dots (RCDs) dominated by surface state emission mechanism were prepared by one-step hydrothermal method, the photoluminescence quantum yield (QY) of RCDs reaches to 78.3% in N,N-Dimethylformamide (DMF). RCDs mainly absorb UV and yellowish green light and emit red light in the region from 550 to 800 nm, which perfectly matches the light needed by plant for photosynthesis. Besides, the fluorescence quenching of RCDs is ascribed to oxidation on the surface of RCDs by oxygen. Further evidences about that are obtained from the changes in fluorescence, singlet oxygen (1O2) signal of RCDs and the amount of O elements between the RCDs and quenched RCDs (QCDs). Antioxidant RCDs/PVA film, served as an agricultural sunlight conversion film, consisting of RCDs, polyvinyl alcohol-1799 (PVA-1799) and ascorbic acid, not only converts yellowish green light (500–610 nm) to red light (610–800 nm) from RCDs with tough, environment-friendly, waterproof properties from PVA-1799, but also gain antioxidant ability on account of ascorbic acid preventing the antioxidant RCDs/PVA film from fluorescence quenching. When antioxidant RCDs/PVA film was applied to the practical agricultural planting, the fresh weight, dry weight and the chlorophyll a content of the mung bean sprouts increased by 10.4% and 13.9%, and 7.1%, respectively. The application of the antioxidant RCDs/PVA film improve the utilization rate of solar energy in agricultural field.