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J. Eur. Opt. Society-Rapid Publ. 21, 6( 2025)
Figure 3. Transmittance curves of the 10 %, 12 %, 15 %, 20 % TiO 2-doped V 2 O 5 / FTO films at the wavelength of 700 nm.
related to the high annealing temperature during the preparation process. By comparison with Figure 4( a) and( b), it shows that the TiO 2 nano powder has been doped into the composite film successfully.
The X-ray diffraction( XRD) profile of the pure V 2 O 5 / FTO film is shown in Figure 5( a). Thediffractiveanglesof 26.36 °, 33.64 °, 37.64 °, 51.40 °, 61.48 °, 65.34 ° correspond to( 110),( 101),( 200),( 211),( 310) and( 301) crystalized planes, respectively being consistent with the SnO 2 standard card( JCPDS. NO. 46-1088). Figure 5( b) shows the XRD profile of the TiO 2-doped V 2 O 5 / FTO film. The diffractive angles of SnO 2 are almost consistent with the undoped film, and the diffractive angles of 20.12 °, 21.56 °, 31.02 °, 40.92 °, 42.38 °, 54.48 ° correspond to( 001),( 101),( 301),( 002),( 102) and( 220) crystalized planes, respectively, which are consistent with V 2 O 5 standard card( JCPDS. NO. 41-1426). The results indicate that the preparation of the TiO 2-doped V 2 O 5 / FTO film has no effect on the crystal structure of FTO, and the main components of the film is composed of V 2 O 5. The partial diffraction angle of( 001) crystalized plane is finely shifted from 20.18 ° to 20.12 ° by comparing with the undoped film, which may due to the changing of the crystal structure of V 2 O 5 after TiO 2-doping. The grain size along the preferred orientation of V 2 O 5 can be obtained according to the Scherrer formula:
D ¼ kk b cos h ð2Þ
Where D represents the grain size, k is the constant factor, k is the wavelength of the X-ray, b is the full width half maximum( FWHM), and h is the Bragg diffraction angle. After calculation, the undoped film has an average grain size of roughly 22.39 nm, while the doped film is about 27.51 nm.
The X-ray photoelectron spectroscopy( XPS) is performed to analyze the composition of the prepared films. Figure 6( a)–( c) show the general spectral line( 0 – 1350 eV),
O 1s and V 2p ofthepureV 2 O 5 / FTO film, and Figure 6( d)–( g) exhibit the general spectral line( 0 – 1350 eV), O 1s, V 2p and Ti 2p of the TiO 2-doped V 2 O 5 / FTO film, respectively. It can be seen in Figure 6( a) and( d) that the films does not contain other elements except O, V, Ti and C elements. In Figure 6( b) and( e), the peaks near 530 eV and 531.5 eV are associated with O 2�, while O � near 533 eV. The appearance of O � peak division indicates that a small part of O elements have defects, resulting in the change from 2 � ions to 1 � ions. It can be found in Figure 6( b) that the O � peak appears a large reduction in contrast of Figure 6( e). The formation of oxygen vacancies is mainly related to the doping of TiO 2 besides the residual HVO 4. The above test results prove the existence of the vacancy. Theory and experiments show that the generation of vacancies makes the film more prone to a crystalline phase transition [ 25 ] and may improve the conductivity of the film. In Figure 6( c) and( f), the peaks near 517.6 eV and 525 eV of two orbital levels are associated with V 5 +, while V 4 + near 515.8 eV and 523.8 eV. The less amount of V element presents 4 + state, which may be explained by the impurity of the V 2 O 5 powder. The V 5 + dominant peak and the V 4 + inferior peak are in line with expectations. In Figure 6( g), the Ti peaks of occurring near 458.6 eV and 464.2 eV were 4 + ions, indicating that the TiO 2 powder maintains its original morphology after incorporation.
Figure 7 displays the transmittance of the pure V 2 O 5 / FTO film and the TiO 2-doped V 2 O 5 / FTO film in the wavelength range of 400 – 1600 nm at different temperatures from 20 ° C to 360 ° C. To ensure the measurement stability during the experiment, the heating rate was kept at 2 ° C / min in measurement. Figure 7( a) shows the transmittance variations of the pure V 2 O 5 / FTO film in 400 – 1600 nm band. The film achieves a maximum transmittance of 62.084 % at the wavelength of 700 nm at 150 ° C. Figure 7( b) shows the transmittance variations in the 400 – 1600 nm band of the TiO 2-doped V 2 O 5 / FTO film. The film achieves a maximum transmittance of 75.807 % at the same conditions. As can be seen from the figure, the incorporation of TiO 2 obviously improves the transmittance of the film at different temperatures. In the temperature range of 20 – 150 ° C, the transmittance of both films gradually increases, speculating that the increasing trend is mainly due to the hydrophilic of the film [ 26 ]. In the temperature range of 150 – 360 ° C, the transmittance of both films decreases, and it decreases most significantly from 250 ° C to 300 ° C, indicating that the phase transition has occurred in this range. The maximum optical modulation amplitude h( k) is used to visualize the regulation properties of the films and it can be obtained by the following formula: hðkÞ ¼ T max ðkÞ�T min ðkÞ ð3Þ
Where T max( k) andT min( k) are the maximum and minimum transmittance of a certain wavelength under the test conditions, respectively. As shown in Figure 7( c), the maximum optical modulation amplitude of the pure V 2 O 5 / FTO film is 8.619 % at 700 nm, and the average optical modulation amplitude in 400 – 1600 nm band is 4.450 %. The maximum optical modulation amplitude of