Flame aerosol deposition of Y2O3:Eu nanophosphor screens and their photoluminescent performance.

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.

Bottom-up Fabrication of Multilayer Stacks of 3D Photonic Crystals from Titanium Dioxide.

A strategy for stacking multiple ceramic 3D photonic crystals is developed. Periodically structured porous films are produced by vertical convective self-assembly of polystyrene (PS) microspheres. After infiltration of the opaline templates by atomic layer deposition (ALD) of titania and thermal decomposition of the polystyrene matrix, a ceramic 3D photonic crystal is formed. Further layers with different sizes of pores are deposited subsequently by repetition of the process. The influence of process parameters on morphology and photonic properties of double and triple stacks is systematically studied. Prolonged contact of amorphous titania films with warm water during self-assembly of the successive templates is found to result in exaggerated roughness of the surfaces re-exposed to ALD. Random scattering on rough internal surfaces disrupts ballistic transport of incident photons into deeper layers of the multistacks. Substantially smoother interfaces are obtained by calcination of the structure after each infiltration, which converts amorphous titania into the crystalline anatase before resuming the ALD infiltration. High quality triple stacks consisting of anatase inverse opals with different pore sizes are demonstrated for the first time. The elaborated fabrication method shows promise for various applications demanding broadband dielectric reflectors or titania photonic crystals with a long mean free path of photons.

Facile deposition of YSZ-inverse photonic glass films.

An alternative all-colloidal and single-step deposition method of yttrium-stabilized zirconia (YSZ)-infiltrated polymeric photonic glass films is presented. Heterocoagulation of oppositely charged polystyrene (PS) microspheres and YSZ nanocrystals in aqueous dispersions created PS/YSZ core-shell spheres. These composite particles were deposited on glass substrates by a simple drop-coating process. Heterocoagulation impaired self-assembly of the particles, resulting in a disordered structure. Burn-out of the polymer yielded a random array of YSZ shells. The effect of the filling fraction of YSZ between these shells was explored. YSZ-inverse photonic glass films with a thickness below 40 µm achieved 70% reflectance of the incident radiation over a broad wavelength range between 0.4 and 2.2 µm. The YSZ structures demonstrated structural stability up to 1000 °C and maintained high reflectance up to 1200 °C for several hours, thus enabling applications as broadband reflectors at elevated temperatures.

Vertical convective coassembly of refractory YSZ inverse opals from crystalline nanoparticles.

A facile deposition method of 3D photonic crystals made of yttrium-stabilized zirconia (YSZ) was developed. YSZ nanoparticles with primary particle size below 10 nm and cubic crystalline phase were synthesized by hydrothermal treatment of solutions of zirconyl nitrate, yttrium nitrate and acetylacetone. Before coassembly with polystyrene (PS) microspheres, a dispersant Dolapix CE64 was added to the dialyzed sol of YSZ nanoparticles to render their surface negatively charged. Vertical convective coassembly resulted in 3D ordered YSZ/PS hybrid films, which were inverted at 500 °C in air to produce inverse opals. The linear shrinkage of the coatings was in the range 15-20%, below previously reported values for YSZ. The obtained coatings demonstrated pronounced photonic properties and retained their ordered structure after annealing at 1000 °C for 2 h. Increasing the filling fraction of crystalline nanoparticles in the templates should enable production of fully functional 3D photonic crystals for applications in high-temperature photonics.