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.
Highlights
The extinction behavior of Nax WO3 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 dopant M cation can contribute a number of electrons to reduce part of the hexavalent tungsten to pentavalent, which makes tungsten bronzes have special physical and chemical properties such as superconductivity [1], photochromism [2], electrochromism [3], photothermal conversion [4] and transparent heat-shielding properties [5], etc
The transparent heat-shielding properties have been studied extensively in recent years because the tungsten bronze exhibits low absorption of visible light and high absorption of near-infrared light (NIR), which meets the demand of smart windows with high visible transmittance and heat-shielding performance
Summary
Tungsten bronze is a kind of solid solution formed by other cations filling in the lattice structure of WO3. The dopant M cation can contribute a number of electrons to reduce part of the hexavalent tungsten to pentavalent, which makes tungsten bronzes have special physical and chemical properties such as superconductivity [1], photochromism [2], electrochromism [3], photothermal conversion [4] and transparent heat-shielding properties [5], etc. The size of dopant cation M determines the content and position of M in the structure of tungsten bronze. As the x increases from 0 to 1, the color of Nax WO3 gradually changes from lime green to dark blue, violet, pink, orange and yellow [10] This change in color can be attributed to increase of bulk plasma frequency (ω p ) [6]. In order to more systematically study the optical properties of nanocrystalline Nax WO3 , the discrete dipole approximation (DDA) method was used to investigate the influence of different x, particle size and particle shape on its optical properties
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