Screens of Y(2)O(3):Eu(3+)-nanophosphor (d(BET) = 24 nm) with coating densities in the range 0.23-3.8 mg cm(-2) were obtained by flame aerosol deposition (FAD) from nitrate-based precursors. The average deposition rate was 0.22 mg cm(-2) min(-1). Porosity of the obtained deposits was 0.973 +/- 0.004. Light scattering of the coatings in the visible range showed a Rayleigh-like dependence on wavelength and, in comparison to the screens made of the commercial micrometer-sized phosphor powder (d(SEM) = 4 microm), was reduced by up to two orders of magnitude. As a result, the nanophosphor coatings maintained nearly constant brightness in a very wide range of coating densities. Furthermore, it should be expected that a substantially improved screen resolution can be achieved with such screens. For excitation at a wavelength of 254 nm, the maximum brightness of the FAD-deposited (Y(0.92)Eu(0.08))(2)O(3) phosphor screens in the transmission mode was nearly one third of that of the screens made of the commercial phosphor. It was demonstrated that light reflection from the supporting substrate and porosity of the coating significantly influence its photoluminescent performance.
The feasibility of stacking of thin ceramic inverse opals with incommensurable periodicity constants was investigated. Inverse opals with photonic stopgaps in the infrared range were prepared by the vertical convective self-assembly from aqueous suspensions of monodisperse polystyrene (PS) particles with the sizes of 476, 608, and 756 nm. The opal templates were infiltrated with TiO 2 by a low-temperature atomic layer deposition process using titanium isopropoxide and water as precursors. The second PS template could be deposited on top of the infiltrated opal layer after exposing the latter to the UV-light, which rendered its surface hydrophilic. Finally, the sacrificial PS templates were removed by calcination at 500°C. It is shown that smoothness of the surface of the inverse opals is crucial for the photonic performance of the heterostructures. Two well-defined stopgaps could be observed in the spectra of reflectance of the stacked inverse opals with improved surface morphology.
The infrared (IR) transmission and reflection properties of the ceramic thermal barrier coatings have great implications on the overall performance of a component operated at high temperatures, where a significant amount of heat from external IR radiation will propagate through the coating toward the underlying substrate. A hightemperature photonic structure can be used to limit this radiation transport while operating at temperatures above 1000°C. Herein, we present the concept of a broadband and angle-insensitive IR reflector, based on 3D photonic crystals (PhCs) that consists of a ceramic material with high thermal stability and low thermal conductivity. We numerically demonstrate that the multistack ceramic 3D PhCs can provide >80% of bi-hemispherical reflectance in the wavelength region of 1-5 μm.
Inverse opals are most widely used as photonic crystals for ultraviolet, optical, and infrared applications. [1] These highly interconnected porous structures are also attractive for applications such as sensors, fuel cells, filters, and catalysts. [2] At the same time, engineers are aiming for lightweight structures with optimized mechanical strength, often inspired by nature's cellular materials with foam-like structures such as sponges, [3] trabecular bone, [4] or plant parenchyma. [5] The resultant optimized strut-based structures have shown high stiffness-and compressive strength-to-weight ratios, [6][7][8][9] but can suffer from strut buckling and a lack of mass production techniques. Here, we show that mechanical metamaterials based on ceramic inverse opaline structures with densities in the range of 330-910 kg m À3 are not only suitable as photonic crystals but also show better stiffness-and compressive strength-to-weight ratios compared to microfabricated optimized strut-based structures, [6][7][8][9] but lower than carbon nanoframes fabricated by interference lithography. [10] Pure silica inverse opal structures and silica inverse opals whose pores have been internally coated by a thin TiO 2 layer have been fabricated and their structural and mechanical behavior was investigated. Our experimental results, supported by numerical simulations, show that these arch-shaped porous structures outperform both strut-based and honeycomb structures due to their nearly isotropic mechanical response.The silica inverse opal films presented here are fabricated by vertical co-assembly based on the procedure described by Hatton et al. [11] Monodisperse colloidal polystyrene (PS) spheres were mixed in a water-based suspension containing tetraethylorthosilicate (TEOS) solution and vertically assembled on soda-lime silica glass. The resulting FCC opaline structure was calcined at 500°C for 30 min to burn out the PS template leaving an inverse-FCC opaline structure of nanoporous amorphous silica in which the adjacent pores are interconnected by %170 nm diameter holes (Figure 1a). Some samples were subsequently coated with an amorphous layer of TiO 2 by atomic layer deposition (ALD). After full crystallization to anatase, the layer thickness was %28 nm (Figure 1b). The specular reflection in Figure 1c shows the characteristic reflection peaks, which can be tuned by both the pore diameter and/or the TiO 2 coating.The effective density of the silica inverse opals was estimated by four independent methods: gravimetric, pycnometric, and two opticals. All four methods yield a comparable density of 330 kg m À3 AE 10%. The effective density of the TiO 2 ALD-coated silica inverse opals was estimated gravimetrically and optically to be 910 kg m À3 AE 10%. Detailed information can be found in the Supporting Information.Some examples of mechanical properties of opaline structures can be found in the literature. These works investigated polymer, [12,13] metal, [14] and ceramic-based [14][15][16] opals. Toivola et al. [15] investigated s...
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