Unusual Fluorescent Properties of Stilbene Units and CdZnS/ZnS Quantum Dots Nanocomposites: White-Light Emission in Solution versus Light-Harvesting in Films

Nanocomposites with organic-inorganic properties represent a new field of basic research and offer prospects for many novel applications in extremely diverse fields, due to their remarkable emerging new properties and multifunctional nature. However, controllable manipulation of their fluorescent properties in different phases is still challenging, which seriously limits the related applications of nanocomposites. In this work, a convenient protocol to fabricate organic-inorganic nanocomposites composed of stilbene chromophores and CdZnS/ZnS quantum dots (QDs) pairs, with controllable fluorescent properties is presented. It is found that stable white-light emission can be achieved only in solution phase, with negligible energy transfer or reabsorption between chromophores and QDs pairs. By contrast, when the nanocomposites are deposited as blended films, they cannot give rise to white-light emission, no matter what donor/acceptor volume ratios are used. However, the blended films can exhibit near-unity efficiency (94%) of Forster resonance energy transfer from QDs to chromophores. The underlying physical mechanisms are revealed through comprehensive steady-state and time-resolved spectroscopic analysis. This work suggests that the CdZnS/ZnS QDs/stilbene nanocomposites can be directly used for fluorescence sensors and probes in biological system as well as fundamental investigation of light-harvesting, and also sheds light on developing other new materials for artificial photosynthesis and optoelectronics.