Sol-gel derived near-UV and visible antireflection coatings from hybridized hollow silica nanospheres

This paper reports a facile means to gradually tailor refractive index from an ultra-low-n of 1.10-1.45 based on hollow silica nanospheres hybridized with acid-catalyzed silica. The influences of the hybridization on refractive index, thin-film uniformity, and roughness were systematically investigated. The single-layered antireflection (AR) coatings and the three-layered AR coatings were prepared using the hybridized thin films as building blocks. The former showed the near-perfect transmittance and reflectance, 99.16 and 0.42 %, respectively, at a single wavelength of 600 nm, while the average transmittance (T (ave)) and reflectance (R (ave)) from the near ultraviolet (UV) to the visible region (300-800 nm) were moderate; the latter demonstrated an excellent AR capability in broadband that T (ave) reaches 97.29 %, much higher than that of the single-layered AR coating, 95.86 %. More interestingly, the three-layered AR coating showed an average transmittance of 97.94 % in the near-UV wavelength range from 345 to 400 nm and it was 6.77 % higher than that of bare glass. Moreover, the three-layered AR coatings had the less degradation in transmission and surface morphology after the highly-accelerated temperature and humidity stress tests, and the wet abrasion scrub tests. The findings imply that both good optical performance and durability are likely to be achieved using the sol-gel derived multilayered AR coatings.