Tunable Transparency and NIR-Shielding Properties of Nanocrystalline Sodium Tungsten Bronzes

Abstract

The NaxWO3 nanoparticles with different x were synthesized by a solvothermal method and the absorption behavior in visible and near-infrared light (NIR) region was studied. Well-crystallized nanoparticles with sizes of several tens of nanometers were confirmed by XRD, SEM and TEM methods. The absorption valley in visible region shifted from 555 nm to 514 nm and the corresponding absorption peak in NIR region shifted from 1733 nm to 1498 nm with the increasing x. In addition, the extinction behavior of NaxWO3 nanoparticles with higher x values were simulated by discrete dipole approximation method and results showed that the changing behavior of optical properties was in good agreement with the experimental results. The experimental and theoretical data indicate that the transparency and NIR-shielding properties of NaxWO3 nanoparticles in the visible and NIR region can be continuously adjusted by x value in the whole range of 0 < x < 1. These tunable optical properties of nanocrystalline NaxWO3 will expand its application in the fields of transparent heat-shielding materials or optical filters.

Extrinsic Oxygen Vacancies Formation during Crystallization of Al2W3O12 by Calcination in Air

“…As shown in Figure , W 4f spectra were acquired for the (a) amorphous precursor powder, (b) A620, and (c) all calcined powders. All Al 2 W 3 O 12 powders exhibited two peaks centered at around 35.9 and 38.0 eV, which were attributed, respectively, to the W 4f7/2 and W 4f5/2 spin–orbit doublets with a separation distance of 2.1 eV. , In addition, it is known that a material can present two types of charge compensation, ionic and electronic. − The first type of charge compensation mechanism, known as ionic, causes the formation of W 5+ or W 4+ species, − which were not found in the studied powders. XPS spectra indicate that only W 6+ is present for both amorphous and A620 powders, as well as in all remaining calcined samples (Figure c), suggesting that the charge compensation is predominantly electronic.…”