Modulating the size and photoluminescence of a copper nanocluster via metal-organic frameworks encapsulating strategy for fluorescence sensing

The photoluminescence modulation of metal nanoclusters has attracted great attention for further application. However, it is still challenging to pursue a simple and controllable strategy for tuning the emission. Herein, a new strategy is developed to modulate the emission of copper nanoclusters (CuNCs) via ZIF-8 encapsulating strategy. During the shell formation process, with increase in ZIF-8 amount, the red emission of CuNCs at 627 nm decreases and a new emission at 450 nm appears. The quantum yield of the optimized CuNCs/ZIF-8 nanocomposites is 17.07%, which is 2.2 times that of CuNCs. Meanwhile, the aggregated states of CuNCs encapsulated into ZIF-8 are gradually transformed to monodispersed states, accompanied by the size decrease from 4.4 nm to 1.0 nm. The mechanism for emission change is attributed to the Cu-centered energy state transformation from triplet state to singlet state, resulting in the blue shift of the CuNCs’ emission. In addition, the addition of Ag+ ions can induce the quenching of the emission of CuNCs/ZIF-8. Based on this, a facile fluorescence sensor is developed for sensitively detecting toxic Ag+ ions and applied to real samples. This strategy for tuning the photoluminescent property of CuNCs may provide a new opportunity for their applications.