Fig. 2: Preparation and optical properties of NIR transparent film.

a Schematic representation of the preparation of the PMMA films of PMI-CBN/DBU. b, c UV–vis–NIR absorption and transmittance spectra of the PMMA films of PMI-CBN and PMI-CBN/DBU. d Photographs of the two films as prepared. e Transmittance spectra of the PMI-CBN/DBU/PMMA films with varying doping ratios of PMI-CBN absorber. f Plots of the transmittances recorded at 480 and 1200 nm versus PMI-CBN absorber doping ratios. g Photographs of the PMI-CBN/DBU/PMMA films with doping contents varied from 0 to 18.2 wt%.