A first blue fluorescence composite film based on graphitic carbon nitride nanosheets/polyoxometalate for application in reversible electroluminescence switching

In this work, for the first time we constructed a multifunctional blue-fluorescence composite film based on photoluminescent protonated graphitic carbon nitride nanosheets (g-C3N4NS) and reversible electrochromic silicomolybdotungstate K8(SiMoW10O39)·13H2O (SiMoW) by the layer-by-layer (LBL) assembly method. Firstly, SiMoW and g-C3N4NS were synthesized, and their structure, morphology and properties were verified by FTIR (Fourier Transform Infrared Spectroscopy), SEM (Scanning Electron Microscopy), CV (Cyclic Voltammetry) and fluorescence spectroscopy. Then, the composite films containing SiMoW and g-C3N4NS were assembled, and their assembly process, morphology, composition and properties were characterized by means of UV-vis absorption spectroscopy, CV, amperometry and fluorescence spectroscopy, XPS (X-ray Photoelectron Spectroscopy) and AFM (Atomic Force Microscopy). Finally, the reversible electrofluorochromic properties of the composite film [(PEI/SiMoW)25/(g-C3N4NS/SiMoW)3/(PEI/SiMoW)2] (PEI: poly(ethyleneimine)) were investigated by in situ spectroelectrochemical systems based on the fluorescence resonance energy transfer mechanism. The results show good blue-fluorescence switching performance, stability and reversibility of this composite film. This is the first demonstration of POM control of blue luminescence switching.