Stable ammonium tungsten bronze (ATB, (NH4)_xWO3) nanoplatelets with high crystallinity were synthesized via a one-step hydrothermal method without using any organic solvent, in which thiourea was employed as reducing agent and sodium tungstale was used as the starting material. The microstructure, phase and optical properties were controlled by varying hydrothermal conditions. The as-prepared samples exhibit a platclet-like morphology with a width range of 30-150 nm and length of 0.3-3 μm. The patterns of X-ray photoelectron spectroscopy (XPS) confirmed the presence of mixed valence states of tungsten. To check the optical properties, (NH4)_xWO3-based films were obtained by uniformly casting its dispersion onto fused silica glass substrates. The films exhibited excellent near-infrared light (NIR) absorption abilities by selectively cut-off NIR region by 66.6% (transmiltancc decreased from 93% of a bare substrate to 26.4% of the films), while maintaining a high visible transmittance of 64.5%, promising its high potential for applications like solar light control filters.
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