Photonic crystals constructed by isostructural metal-organic framework films

Metal-organic framework (MOF)-on-MOF structure allows stacking various types of MOFs with different lattice constants for molecule sieving or filtering. However, the multilayered MOFs-based optical devices have incoherent interference due to the lattice-mismatch at the interface and refractive index (RI) indifference. This paper reports isostructural MOFs-based photonic crystals (PCs) designed by stacking Bragg bilayers of lattice-matched MOFs thin films through a layer-by-layer assembly method. Colloidal nanoparticles (NPs) were homogenously encapsulated in some layers of the MOFs (HKUST-1@NPs) to tune their intrinsic RI during the spraying coating process. The isostructural MOFs-based PCs were constructed on a large scale by sequentially spraying coating the low RI layer of HKUST-1 and high RI layer of HKUST-1@NPs to form the desired number of Bragg bilayers. X-ray photoelectron spectroscopy (XPS) depth profiling proved the Bragg bilayers and the homogenous encapsulation of nanomaterials in certain layers of MOFs. Bandwidth of the PCs was tailored by the thickness and RI of the Bragg bilayers, which had a great consistent with finite difference time domain (FDTD) simulation. Importantly, reflectivity of the isostructural MOFs-based PCs was up to 96%. We demonstrated high detection sensitivity for chemical sensing on the PCs, which could be advanced by encapsulating different types of nanomaterials and designing wide-band isostructural MOFs-based PCs. [Figure not available: see fulltext.]