λ/4-λ/2 Double-layer Broadband Antireflective Coatings with Superhydrophilicity and Photocatalysis

doi:10.15541/jim20180116

Abstract

Abstract:

Antireflective (AR) coatings, which can suppress the undesired interfacial Fresnel reflections, are widely used in optical devices and energy-related instruments. Conventional single-layer quarter-wave AR coatings, which only work at a single wavelength, have been seriously limited in some practical applications because of this inherent property. In this work, broadband AR coatings were designed and prepared based on the concept of λ/4-λ/2 double-layer interference film by Sol-Gel dip-coating method. Substrates (K9 glasses) coated with the double-layer films attained consistent high transmittances at 500-700 nm with an average transmittance of 99.4%, and the average transmittance at visible region was 99.0%. The λ/4-λ/2 broadband antireflective coatings were achieved without low-refractive- index materials. So high-refractive-index TiO₂ could be introduced into the double-layer films to endow the films with self-cleaning property. The double-layer films exhibited outstanding superhydrophilicity with water contact angle of 2.2° in 0.5 s, and the superhydrophilicity lasted for 20 d in the absence of UV illumination. The double-layer coatings also showed a good ability to decompose organic substances under UV irradiation. The broadband of AR coatings with photocatalysis and durable superhydrophilicity may be applied in the fields of opto- and microelectronics.

Key words: broadband antireflective coatings, superhydrophilicity, photocatalytic activity, SiO₂, TiO₂

CLC Number:

LI Yuan-Yang, JIANG Bo. λ/4-λ/2 Double-layer Broadband Antireflective Coatings with Superhydrophilicity and Photocatalysis[J]. Journal of Inorganic Materials, 2019, 34(2): 159-163.

Figures/Tables 8

Fig. 1 Simulated transmittance spectra of modeled double- layer coatings with the refractive index of bottom layer of 1.6

Fig. 2 Transmission spectra of simulated and experimental double-layer AR coatings compared with that of bare K9 glass

Fig. 3 Time-dependent variations of (a) 0.5 s spreading and (b) static water contact angle of TiO2, TiO2-SiO2 and double- layer films Insets: water contact angle images of the double-layer film for 0, 30 d and 60 d

Fig. 4 FT-IR spectra of SiO2 film, TiO2 film and double-layer film

Fig. 5 AFM surface topographies of (a) TiO2 film, (b) TiO2- SiO2 composite film (20wt% TiO2), and (c) double-layer film

Fig. 6 Evolution of FT-IR spectra of stearic acid coated double- layer film with UV illumination

Fig. S1 (a) Changes of refractive indexes of composite films as a function of TiO2 content, (b) Changes in refractive index of 20wt% TiO2 containing composite films as a function of F127 content in sols

Fig. S2 XRD pattern of the TiO2 powder heat-treated at 400 ℃

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