Designing multifunctional silica coatings for enhanced broadband antireflection and microfiber contamination sensing

Multifunctional silica coatings find diverse applications in solar energy conversion and pollution monitoring sensors due to their suitability for mass manufacturing. However, the challenge lies in producing robust silica coatings on a large scale with tunable refractive index. This work presents a two-step acid/base catalyzed sol–gel process for synthesizing multifunctional silica coatings with adjustable refractive index. The coatings' porous microstructure allows them to be used as double-layer broadband antireflective coatings and enhances the sensitivity of contamination sensors. The optimized double-layer coatings, designed using computer-aided techniques, demonstrate excellent broadband antireflective performance in the visible regions and high environmental durability. They achieve a maximum transmittance of 99.87% at 591 nm, with an average transmittance of 99.40% in the visible region (400–800 nm) and 98.63% from 400 nm to 1100 nm. Additionally, the coatings exhibit robust abrasion resistance and enhanced surface hydrophobicity with a water contact angle increased from 30° to 126° through HMDS treatment. This work investigated the particle growth mechanism and the relationship between silica nanoparticle microstructure and antireflective coating properties. Furthermore, the coatings' presence of abundant micropores allows successful application onto microfiber contamination sensors, the additional loss increases from 26.40 dB to 37.69 dB over 140 min and decreases to 31.55 dB within one minute, demonstrating rapid adsorption and desorption rates. The work successfully achieves a wide range of adjustable refractive index while maintaining excellent mechanical and optical properties, addressing the traditional trade-off between high porosity and poor mechanical stability. These rationally designed multifunctional silica coatings hold great potential for high-quality broadband antireflection and high sensitivity in microfiber contamination sensing.