Three-layer multifunctional vanadium dioxide-fluorescent brightener-organic polymer composite films

Vanadium dioxide (VO₂) is a typical thermochromic material that can be used for smart windows, which can effectively reduce the building energy consumption. However, the issues of the yellow brown color and instabi-lity of VO₂ based smart glass restrict its wide application. Herein, a series of VO₂ based three-layer fluorescent composite films has been reported. The composite films consist of VO₂@SiO₂ based thermochromic layer, fluorescent brightener layer and organic polymer layer. The VO₂@SiO₂ layer can control the sunlight intake with the change of external temperature, regulating the indoor temperature, with the core-shell structure improving the stability of the film. The fluorescent brightener layer absorbs ultraviolet irradiation and emit blue fluorescence, thus improving the color of VO₂ coating. As the top layer, the organic polymer layer can effectively protect the lower layers and increase the stability of the whole composite film. Compared with the pure VO₂ films, these composite films not only maintain high visible light transmittance and solar modulation ability, but also reversibly change color from yellow-brown to blue under sunlight. Meanwhile, the stability and the UV blocking property are also significantly improved. The properties of this type of composite films are beneficial to the promotion and application of VO₂-based smart windows.