Selective UV Reflecting Mirrors Based on Nanoparticle Multilayers

Abstract

A new type of nanostructured selective ultraviolet (UV) reflecting mirror is presented. Periodic porous multilayers with photonic crystal properties are built by spin‐coating‐assisted layer‐by‐layer deposition of colloidal suspensions of nanoparticles of ZrO2 and SiO2 (electronic band gap at λ < 220 nm). These optical filters are designed to block well‐defined wavelength ranges of the UVA, UVB, and UVC regions of the electromagnetic spectrum while preserving transparency in the visible. The shielding against those spectral regions arises exclusively from optical interference phenomena and depends only on the number of stacked layers and the refractive index contrast between them. In addition, it is shown that the accessible pore network of the as‐deposited multilayer allows preparing thin, flexible, self‐standing, transferable, and adaptable selective UV filters by polymer infiltration, without significantly losing reflectance intensity, i.e., preserving the dielectric contrast. These films offer a degree of protection comparable to that of traditional ones, without any foreseeable unwanted secondary effects, such as photodegradation, increase of local temperature or, as is the case for organic absorbers, generation of free radicals, all of which are caused by light absorption.

Graphene Oxide Transparent Hybrid Film and Its Ultraviolet Shielding Property

“…Although the transmittance at 500 nm decreased as GO content increasing, when hybrid film containing 1.2 wt % GO, 97.5% of UV light can be shielded, 44.3% of visible light still can be transmitted, which illustrates good UV shielding and visible transparency. The UV-shielding performance of obtained films is much comparable to that using other inorganic UV-absorbers, 5,25 which indicates GO can be used as a good UV-absorber for predation of transparent UV shielding hybrid film.…”

Printing of Large‐Scale, Flexible, Long‐Term Stable Dielectric Mirrors with Suppressed Side Interferences

“…Through steady progress within the group of H. Míguez, they were able to reduce the annealing temperature of nanoparticle-based dielectric mirrors (three double layers of SiO 2 and TiO 2 , maximum reflectance of 70-80% at λ 0 ≈ 400-800 nm, or ten double layers of SiO 2 and ZrO 2 , maximum reflectance of 80% at λ 0 ≈ 230-320 nm) again down to room temperature in 2009/2010. [3,[16][17][18] The next step toward large-scale processing, homogeneous and, even flexible dielectric mirrors, was made by utilizing polymer-nanocomposite inks or polymers only. Such inks combine the advantages of organic polymers (flexibility, solubility, printability, and cheap) with the advantages of inorganic materials (high refractive indices, good chemical resistance).…”

“…Dielectric mirrors do not only serve as a light management tool for radiation shieldings, anti-reflection coatings, efficiency enhancement in semitransparent photovoltaics, light guiding in emitting devices, but also as sensors or encapsulants. [1][2][3][4][5][6] The discovery of dielectric mirrors started along with the theoretically description of interference effects at thin films in the early 20th century. Quickly realizing their great potential, the first anti-reflection coatings fabricated by physical vapor deposition of inorganic materials for rifle-scopes and binoculars had already been established during the Second World War.…”

Optical Design of Porous ZnO/TiO2 Films for Highly Transparent Glasses with Broadband Ultraviolet Protection

“…Unfortunately, as increases in UV absorptive materials, the extinction coefficients in UV region also decrease, causing reduced UV absorption. To compensate this degradation, different UV absorbers with high extinction coefficients in each UV region (i.e., UVA and UVB) are used in the form of nanocomposites or multilayer structures [19,20]. However, despite several studies of nanostructures for transparent UV protection, optical analysis and design have hardly been conducted to optimize UV absorbers for high visible-light transparency, and only studies adopting the reflection effect such as 1D photonic crystal or Bragg mirror have been conducted [21][22][23].…”