Towards high-powered remote WLED based on flexible white-luminescent polymer composite films containing S, N co-doped graphene quantum dots

In this article, a new application of using S, N co-doped graphene quantum dots (S, N-GQDs) as ideal color converters in solid-state white light-emitting diode (WLED) is reported. To this end, the S, N-GQDs with an average diameter of ∼4.46 nm are obtained by a hydrothermal approach using citric acid and thiourea as source materials. The PL spectra of S, N-GQDs show an excitation-independent behavior in the range of 300–380 nm. Under UV illumination, the S, N-GQDs display intense blue-light with the quantum yield of 51.2%. The PL mechanism is also investigated. Then, we fabricate freestanding luminescent composite films in a solution casting method by combining S, N-GQDs with YAG:Ce³⁺ phosphors based on a polyvinyl alcohol (PVA) matrix. The luminescent films have superior foldability and photostability and excellent heat resistance, and retain their optical performances in the solid-state. To realize their potential, a high-powered remote WLED has been demonstrated. The results indicate that S, N-GQDs and YAG:Ce³⁺ can be homogeneously dispersed in the PVA without aggregation so that uniform white-light emission can be obtained. These composite films containing S, N-GQDs are promising to be used in state-of-the-art UV-pumped remote WLED according to their wide wavelength emission and collapsible illumination device.