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Abstract We demonstrate shear‐printed layered photonic films with vivid structural coloration from bio‐derived cellulose nanocrystals and highly aligned Ti3C2TxMXene nanoflakes. These ultrathin films (700–1500 nm) show high light transmittance above 40% in the visible range. In reflectance mode, however, the films appear vividly colored and iridescent due to the multiple distinct photonic bandgaps in the visible and near‐infrared ranges, which are rarely observed in CNC composites. The structural coloration is controlled by the stacking of MXene nanoscale‐thin layers separated by the thicker cellulose nanocrystals matrix, as confirmed by photonic simulations. The unique combination of distinctly different optical appearances in transmittance and reflectance modes occurs in films printed with just a few layers. This is because of the molecularly smooth interfaces and the high refractive contrast between bio‐based and inorganic phases, which result in a concurrence of constructive and destructive interference. These lamellar biophotonic films open the possibilities for advanced radiative cooling, camouflaging, multifunctional capacitors, and optical filtration applications, while the cellulose nanocrystals matrix strengthens their flexibility, robustness, and facilitates sustainability.
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Multilayer dielectric reflector using low-index nanolattices
Dielectric mirrors based on Bragg reflection and photonic crystals have broad application in controlling light reflection with low optical losses. One key parameter in the design of these optical multilayers is the refractive index contrast, which controls the reflector performance. This work reports the demonstration of a high-reflectivity multilayer photonic reflector that consists of alternating layers of TiO2films and nanolattices with low refractive index. The use of nanolattices enables high-index contrast between the high- and low-index layers, allowing high reflectivity with fewer layers. The broadband reflectance of the nanolattice reflectors with one to three layers has been characterized with peak reflectance of 91.9% at 527 nm and agrees well with theoretical optical models. The high-index contrast induced by the nanolattice layer enables a normalize reflectance band of Δλ/λoof 43.6%, the broadest demonstrated to date. The proposed nanolattice reflectors can find applications in nanophotonics, radiative cooling, and thermal insulation.
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- Award ID(s):
- 2314268
- PAR ID:
- 10490985
- Publisher / Repository:
- Optical Society of America
- Date Published:
- Journal Name:
- Optics Letters
- Volume:
- 49
- Issue:
- 4
- ISSN:
- 0146-9592; OPLEDP
- Format(s):
- Medium: X Size: Article No. 1093
- Size(s):
- Article No. 1093
- Sponsoring Org:
- National Science Foundation
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