White light-emission based on superstructure ZIF-8⊃CdSe/ZnS quantum dots composite film

In this paper, a white light-emission scheme based on the superstructure ZIF-8⊃quantum dots composite film is proposed. In this scheme, CdSe/ZnS quantum dots (QDs) are encapsulated in-situ within the rhombic dodecahedral ZIF-8 crystals, which are self-assembled to form the superstructure composite film having photonic crystal-like properties. When a blue light is launched to this superstructure composite film, part of the incident light is reflected due to the photonic bandgap of the composite film. The other part of the incident light enters into the composite film, due to either the skin effect of photonic crystals or the incomplete reflection of the photonic bandgap, and excite the QDs within the composite film to emit a yellow fluorescence. Then, the complementary reflected light and emitted fluorescence can be combined as a white light. In this work, the superstructure ZIF-8⊃CdSe/ZnS composite film with an orderly particle arrangement is fabricated, where the adhesion between the film and the substrate and the solvent evaporation temperature are optimized to improve the quality and stability of the superstructure composite film. The morphology, structure and optical properties such as UV-VIS absorption, reflection and photoluminescence spectra of the composite films are characterized. The results show that the particle size of ZIF-8 crystals can be adjusted by controlling the concentration of cetyltrimethylammonium bromide (CTAB) surfactant solution. Among them, for the particle size around 144.9 nm and under excitation with a 470 nm light, the good white light is obtained, where its CIE coordinates are (0.3347, 0.3324). In fact, because of the adjustability of the particle size of ZIF-8 crystals, the selection of incident light and emitted fluorescence has a great degree of freedom, which makes our proposed scheme more flexible.