Enhancing luminescence of AF2: Ln3+ (A = Ca, Sr; Ln = Eu, Tb) by the use of carbon dots

Lanthanide ions-doped fluoride nanocrystals have excellent application prospect. However, low photoluminescence quantum yield (PLQY) is usually along with lanthanide ions-doped fluoride nanocrystals owing to their low molar absorptivity and narrow absorption band. In order to increase the absorption cross section of Ln3+ in fluoride nanocrystals, a facile synthesis strategy to enhance luminescence of AF2: Ln3+ (A = Ca, Sr; Ln = Eu, Tb) by the use of carbon dots (CDs) has been developed in this work. A series of characterizations including TEM, XRD, FTIR and XPS demonstrated that the CDs have been successfully combined with the surface of AF2: Ln3+ nanocrystals. The combination of CDs has little influence on the microstructure and phase structure of AF2: Ln3+, and CDs@AF2: Ln3+ nanocrystals have uniform and regular shape with cubic phase. CDs are used as a broadband sensitizer and lead to the broadband excitation of Ln3+, resulting in the enhancement around 10-fold of Ln3+ luminescence emission in AF2: Ln3+ nanocrystals after CDs combination. The corresponding PLQY increases almost three times, and the luminescence enhancement mechanism by combining CDs is proposed. In addition, the CDs@AF2: Ln3+ nanocrystals are used to prepare CDs@AF2: Ln3+/PVA films, which exhibits excellent luminescence properties under the excitation of UV light. This work provides a superior method for enhancing the luminescence properties of lanthanide ions-doped nanocomposites and demonstrates practical potential as promising candidates for light-converting thin films.