CHARACTERISTICS AND OPTICAL PROPERTIES OF Fe 3 + DOPED SiO 2 / TiO 2 THIN FILMS PREPARED BY THE SOL-GEL DIP-COATING METHOD

In this study, we have successfully synthesized Fe doped SiO2/TiO2 thin films on glass substrates using the sol-gel dip-coating method. After synthesizing, the samples were annealed at 500C in the air for 1 hour. The characteristics and optical properties of Fe doped SiO2/TiO2 films were then investigated by X-ray diffraction (XRD), ultraviolet-visible spectroscopy (UV-vis) and Fourier transform infrared spectroscopy (FT-IR). An antifogging ability of the glass substrates coated with the fabricated film is investigated and explained by a water contact angle under visible-light. The analyzed results also show that the crystalline phase of TiO2 thin films comprised only the anatase TiO2, but the crystalline size decreased from 8.8 to 5.9 nm. We also observed that the absorption edge of Fedoped SiO2/TiO2 thin films shifted towards longer wavelengths (i.e. red shifted) from 371.7nm to 409.2 nm when the Fe-doped concentration increased from 0 to 1 % mol.


INTRODUCTION
Titanium dioxide (TiO 2 ) is a nontoxic material and has been applied in environmental treatments such as water and air purification, water disinfection and sterilization because of Its unique properties such as strong photocatalytic activity and chemical stability [1].However, the major limitations of TiO 2 are the absorption region in the UV light (about 4% -5% of solar energy) and fast recombination of hole-electron pairs within nanoseconds.To propose using TiO 2 to the coating on the ceramic tiles and glass to make intelligent materials was being able selfcleaning and antibacterial.In our previous papers [2,3]

EXPERIMENTAL
The  The volume of H 2 O containing 1 wt% HCl can be determined by the formula: (1) In this report, we synthesized the Fe 3+doped SiO 2 /TiO 2 coating solution with various Fe/(SiO 2 +TiO 2 ) molar ratios: from 0 to 1%.
The Fe 3+ -doped SiO 2 /TiO 2 thin films were deposited on glass substrates by a dip coating process at room temperature.Glass slides with dimensions of (26x76) mm 2 were used as substrates.Before the deposition, the substrates were ultrasonically cleaned in dilute HCl, acetone and absolute ethanol for 30 min, respectively.Finally, they were thoroughly rinsed with DI water.
The substrates were immersed into asprepared Fe-doped SiO 2 /TiO 2 sol for 30 seconds.The substrates were then withdrawn from the sol with velocity 5 mm/s.If coating two times or more, each layer would be dried between two successive coatings at 230 0 C for 5 min before the next coating was implemented.
Afterward, the substrates were annealed at

X-ray diffraction Measurements
XRD patterns for undoped and various )Nitrate Fe(NO 3 ) 3 .9H 2 O (Merck), DI water.The synthesis process of the Fe-doped SiO 2 /TiO 2 solution is shown in Figure 1.

Figure 1 .
Figure 1.The synthesis process of the Fe 3+ -doped SiO 2 /TiO 2 solution prepared soil-gel method Bruker) in the range 400-4000 cm − 1 by the KBr pellet technique.

Figure 2 .
Figure 2. The UV-vis spectra of SiO 2 /TiO 2 thin films with different Fe-doped concentrations in the wavelength range of 300-800 nm.The ultraviolet-visible (UV-Vis) spectra of SiO 2 /TiO 2 thin films with different Fe 3+doped concentrations in the wavelength range of 300-800 nm are illustrated in Figure 2. It reveals that the transmittance of SiO 2 /TiO 2 thin film without Fe 3+ doping has an abrupt decrease when wavelengths are below 350 nm.This indicates the absorption edge near 350 nm

FeFigure 4 .
Figure 4 also reveals that the intensity of diffraction peaks decreases with an increasing Fe 3+ -doped concentration.This phenomenon caused by the Fe 3+ -doped can inhibit the crystallization of anatase TiO 2 [11].

Figure 5 .Figure 6 .
Figure 5.Effect of Fe 3+ -doped concentrated on the crystalline size of TiO 2 thin films.It reveals that the size of TiO 2 powder decreases from 8.8 to 5.59 nm when the Fe 3+doped concentration increases from 0 to 0.8 mol%.The Fe 3+ -doped has an effect on the crystallization of TiO 2[9].The larger the amount of Fe 3+ -doping, the wider the width of the diffraction peaks, the worse the crystallization, and the smaller the grain size of TiO 2 powders.

Figure 6 Figure 7 .Figure 8 .
Figure6shows the Raman spectra of different samples.Raman peak at about 144 cm −1 is observed for all the samples, which is attributed to the main E g anatase vibration mode.Moreover, vibration peaks at 395 cm −1 , 518 cm −1 and 639 cm −1 are presented in the spectra for all samples, which indicate that anatase TiO 2 crystalline are the predominant species.Furthermore, there is no peak attributed to the iron oxide observed, which is consistent with the results of XRD patterns.

Figure 8
Figure 8 shows that the dependence of photo-induced changesin the water contact angle of Fe 3+ -doped SiO 2 /TiO 2 thin film with Fe 3+ 0.8 mol % coated on glass, which were irradiated under visible-light after 2 hours and then kept 1 day in a dark environment.The hydrophilic ability of the sample may be explained by the contact angle of water on the surface.The super-hydrophilic property of the surface allows water to spread completely across the surface rather than remaining as droplets.The observed result means that Fe 3+doped SiO 2 /TiO 2 film coated glass is a good material for antifogging and self-cleaning purposes.

PHAÙ T TRIEÅ N KH&CN, TAÄ P 16, SOÁ K1-2013 Trang 93 into
we have reported the influence of the crystal lattice of TiO 2 .Furthermore, Fe 3+ ions can play a role as e -/h + pair traps because the energy level of Fe 2+ /Fe 3+ lies close to that of Ti 3+ /Ti 4+ , favoring the separation of -/h + pair recombination rate[6,10].

Table 2 .
From the value of E g (eV) and λ ht