Vertical convective coassembly of refractory YSZ inverse opals from crystalline nanoparticles

Optoelectrical Regulation of CuBi2O4 Photocathode via Photonic Crystal Structure for Solar-Fuel Conversion

Metal oxide semiconductors have been regarded as ideal candidates for photoelectrochemical (PEC) CO₂ reduction if the contradiction between photon harvesting and photocarrier collection can be resolved. The novel three-dimensional structure provides an available approach to balancing the above-mentioned contradiction. In this work, CuBi₂O₄ photonic crystal photocathodes with different feature sizes were developed to realize the regulation of optoelectrical properties. The resulted photocathode displays promoted PEC activity as the enhanced photocurrent and CO₂ reduction activity. Such an excellent performance was attributed to the improved efficiency of charge carrier generation and collection through extending the optical path and shortening the carrier transport distance inside films. COMSOL simulations and PEC spectroscopy analysis confirmed the promoted photon harvesting capacity and carrier dynamics. This work demonstrates a feasible strategy for developing novel photocathodes with modulated microstructures in solar-fuel conversion.

Gold Nanoparticles in Photonic Crystals Applications: A Review

This review concerns the recently emerged class of composite colloidal photonic crystals (PCs), in which gold nanoparticles (AuNPs) are included in the photonic structure. The use of composites allows achieving a strong modification of the optical properties of photonic crystals by involving the light scattering with electronic excitations of the gold component (surface plasmon resonance, SPR) realizing a combination of absorption bands with the diffraction resonances occurring in the body of the photonic crystals. Considering different preparations of composite plasmonic-photonic crystals, based on 3D-PCs in presence of AuNPs, different resonance phenomena determine the optical response of hybrid crystals leading to a broadly tunable functionality of these crystals. Several chemical methods for fabrication of opals and inverse opals are presented together with preparations of composites plasmonic-photonic crystals: the influence of SPR on the optical properties of PCs is also discussed. Main applications of this new class of composite materials are illustrated with the aim to offer the reader an overview of the recent advances in this field.

Determination of the packing fraction in photonic glass using synchrotron radiation nanotomography

Photonic glass is a material class that can be used as photonic broadband reflectors, for example in the infrared regime as thermal barrier coating films. Photonic properties such as the reflectivity depend on the ordering and material packing fraction over the complete film thickness of up to 100 µm. Nanotomography allows acquiring these key parameters throughout the sample volume at the required resolution in a non-destructive way. By performing a nanotomography measurement at the PETRA III beamline P05 on a photonic glass film, the packing fraction throughout the complete sample thickness was analyzed. The results showed a packing fraction significantly smaller than the expected random close packing giving important information for improving the fabrication and processing methods of photonic glass material in the future.

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.

Green Color Purification in Tb(3+) Ions through Silica Inverse Opal Heterostructure

The ordered SiO2:Tb(3+) inverse opal heterostructure films are fabricated through polystyrene spheres hetero-opal template using the convective self-assembly method to examine their potential for color purification. Their optical properties and photoluminescence have been investigated and compared with individual single inverse opals and reference (SiO2:Tb(3+) powder). The heterostructures are shown to possess two broad photonic stop bands separated by an effective pass band, causing suppression of blue, orange, and red emission bands corresponding to (5)D4 → (7)F(j); j = 6, 4, 3 transitions, respectively and an enhancement of green emission (i.e., (5)D4 → (7)F5). Although the suppression of various emission occurs because of its overlap with the photonic band gaps (PSBs), the enhancement of green radiation is observed because of its location matching with the pass band region. The Commission International de l'Eclairage (CIE) chromaticity coordinates of the emission spectrum of the heterostructure based on polystyrene sphere of 390 and 500 nm diameter are x = 0.2936, y = 0.6512 and lie closest to those of standard green color (wavelength 545 nm). In addition, a significant increase observed in luminescence lifetime for (5)D4 level of terbium in inverse opal heterostructures vis-à-vis reference (SiO2:Tb(3+) powder) is attributed to the change in the effective refractive index.

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.