The composition content and structure of the tungsten bronze can be analyzed and measured by UV-visible spectrum. Figure 1 is the UV diffuse reflectance spectra of Ta_xWO₃ sample, the figure shows the main absorption peak of Ta_xWO₃ crystals is between 450 ~ 500nm, with significant ultraviolet light absorption, a clear absorption edge, the absorption band edge is determined to inflection point of the absorption band edge. With the increase of the amount of tantalum doping, there is red shift at the absorption peak position, the absorption intensity increased, probably because the tungsten oxide crystal structure introduced low tantalum ions and left oxygen vacancies within the material, and with tantalum doping increasing, the ratio of oxygen vacancies increased, resulting in different light absorbing characteristics of the tantalum doped tungsten oxide.

 

Different values of the absorption edge because tungsten oxide prepared with different amount of tantalum doped, according to the relational expression (1) of the light absorption threshold λg of a semiconductor and bandgap energy Eg, the tantalum doped tungsten oxide bandgap can be calculated. Figure 2 shows changing relationship between the doped tantalum tungsten oxide bandgap and the amount of the doping of tantalum. The figure shows that with the increasing of the amount of tantalum doping, bandgap decreases from undoped tungsten oxide band gap of 3.17keV gradually to 2.74keV. There is red shift at Ta_xWO₃ absorption wavelength mainly due to Ta ion doping effect, since the Ta ions formed a new impurity level between the conduction band and valence band, which reduced the electron transition energy gap.