Abstract
Angle independent non-absorbing spectral filters are required for many applications such as sunscreens, structural colors, photovoltaics, and radiative cooling. One of the promising and simple to manufacture structures is based on the disordered arrangement of monodisperse spherical particles by self-assembly, also called photonic glasses. So far, reported photonic glasses inherently show poor spectral selectivity with a smooth transition in reflection. No significant improvement is usually expected from particles optimization as the Mie resonances are broad for small dielectric particles with a moderate refractive index. Via Fourier space engineering, we show here that it is, nonetheless, possible to obtain sharp spectral transitions from the synergetic effect of a core-shell geometry of the particles with the short range order of the photonic glass. We apply the developed approach to demonstrate a high color saturation of a non-iridescent blue structural color employing a photonic glass with hollow sphere particles, which features a sharp spectral transition in reflection. The experimental results support the theoretical predictions from the first-order approximation.
Highlights
The length of ⃗kin is defined as nbω/c, where ω is the frequency, c is the speed of light in vacuum, and nb is the refractive index of the background material
We devised a completely new design scheme based on Fourier space engineering for realizing non-absorbing non-iridescent spectral filters with high spectral selectivity based on disordered photonic glass (PhG)
While the non-iridescence stems from the disordered arrangement of the PhG, the high spectral selectivity is obtained by the optimization of the particle geometry in relation to the particle arrangement
Summary
Angle independent (non-iridescent) non-absorbing spectral filters are required for many applications which can cover wavelength regions from ultraviolet (UV) to mid-infrared (MIR). To protect the human skin from sunburn by the UV radiation, sunscreens need to effectively block UV radiation, while being able to transmit visible light in order to avoid the unwanted whitening effect on the skin. it would be beneficial to have nonabsorbing sunscreens, which would reflect UV rather than absorbing the radiation since this could lead to unwanted photocatalytic effects in the skin. In addition, such selective reflecting structures could be bigger in size than the titania nanoparticles used today, which reduces the risk of nanoparticle uptake into the organism. At visible wavelengths, angle independent spectral filters can be used to obtain non-iridescent structural colors by moving the reflection transition into the visible range. Since conventional pigments derive their colors from selective light absorption which is connected to their chemical structure, a saturated color based on non-toxic materials of high UV and chemical stability has been difficult to achieve. The promising alternative is non-iridescent structural colors based on spectrally selective light scattering from nanostructures, which depends only on the refractive index distribution and can be produced from non-absorbing and environmentally friendly materials of high light-fastness. Angle independent (non-iridescent) non-absorbing spectral filters are required for many applications which can cover wavelength regions from ultraviolet (UV) to mid-infrared (MIR).. It would be beneficial to have nonabsorbing sunscreens, which would reflect UV rather than absorbing the radiation since this could lead to unwanted photocatalytic effects in the skin.. It would be beneficial to have nonabsorbing sunscreens, which would reflect UV rather than absorbing the radiation since this could lead to unwanted photocatalytic effects in the skin.1 Such selective reflecting structures could be bigger in size than the titania nanoparticles used today, which reduces the risk of nanoparticle uptake into the organism.. Angle independent spectral filters can be used to obtain non-iridescent structural colors by moving the reflection transition into the visible range.. When the reflection edge is shifted to the infrared region, this concept can be further applied to avoid thermal cooling of an incandescent lamp, strongly improving its efficiency or to reflect visible and near infrared radiation and transmit MIR thermal emission for day time radiative cooling.
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