Fluorescent polyvinyl alcohol films based on nitrogen and sulfur co-doped carbon dots towards white light-emitting devices

摘要

Nitrogen and sulfur co-doped carbon dots (NS-CDs) were synthesized via a facile hydrothermal process using citric acid monohydrate as the carbon source and L-cysteine as the additive. The morphology, surface structure and fluorescence properties of as-obtained sample were elaborated in detail. The results show that the size of NS-CDs is about 2.9 nm without any obvious aggregation. Oxygen-, nitrogen-and sulfur-containing functional groups exist on the surface of NS-CDs. As the as-prepared NS-CDs possess promising optical properties, such as high quantum yield (67.41%), strong absorption in UV region and excitation-dependent feature, fluorescent films of the NS-CDs in polyvinyl alcohol (PVA) matrix were prepared. These films exhibit a broad emission covering the entire visible region as with NS-CDs aqueous solution, and a drastically elevated blue-to-red spectral composition (61.30%) compared with NS-CDs aqueous solution (31.60%). Beyond that, white light-emitting diodes, which were produced by dispersing NS-CDs in PVA matrix with a 365 nm UV-LED chip, emit warm white light with a color coordinate of (0.40, 0.38), a correlated color temperature of 3980 K and luminance of 3629 cd m(-2).