Tunable Bragg stacks from sol-gel derived Ta₂O₅and MEL zeolite films

Lithium Tin Sulfide—a High‐Refractive‐Index 2D Material for Humidity‐Responsive Photonic Crystals

“…Although a high RI contrast and good optical device quality were achieved, the sensitivity toward vapors is severely reduced due to the limited textural porosity of the titania layer. Another approach to increase the RI contrast is to identify new porous materials with a similar or even higher RI compared to TiO 2 , although current alternatives such as WO 3 sol ( n = 2.03), ZrO 2 nanoparticles ( n = 1.70), Ta 2 O 5 nanoparticles ( n = 1.80), undoped or antimony‐doped SnO 2 films ( n (undoped) = 1.83, n (3% Sb‐doped) = 2.34) all feature lower RIs compared to dense titania or suffer from low transparency in the visible range. Thus, the highest RI contrast BSs reported so far combine highly porous silica layers stacked with dense titania layers, exhibiting an RI contrast of Δ n = 0.83, Δ n = 0.84, and Δ n = 0.89 .…”

Vapor Responsive One-Dimensional Photonic Crystals from Zeolite Nanoparticles and Metal Oxide Films for Optical Sensing

“…, 500 nm in the current case. In order to achieve the correct thicknesses of the films, the concentrations of the zeolite suspension and Nb sol were optimized by addition of appropriate amount of solvent-ethanol [10,14]. An annealing of the films at 320 °C for 30 min was applied after deposition of the MEL nanozeolite.…”

“…Reflection spectra (R) of zeolite films were measured in the spectral range 320–900 nm using a UV-VIS-NIR spectrophotometer (Cary 5E, Varian, Australia) at normal and oblique incidence of unpolarized and p- and s-polarized light. Refractive index ( n ), extinction coefficient ( k ), and thickness ( d ) of the films were determined simultaneously from the reflection measurements using non-linear curve fitting method described in details elsewhere [10,14]. The experimental errors for the three parameters, n , k and d are 0.005, 0.003 and 2 nm, respectively.…”

“…In this way, responsive one-dimensional structures for optical sensing applications can be prepared. This concept has already been demonstrated for multilayered structures comprising mesoporous TiO 2 and SiO 2 [ 4 ], TiO 2 and synthetic Laponite [ 5 , 6 ], TiO 2 and SiO 2 nanoparticles [ 7 , 8 ], SiO 2 and SnO 2 , SiO 2 and Sb-doped SnO 2 [ 9 ], zeolite nanoparticles and TiO 2 and ZnO particles [ 6 ] or Ta 2 O 5 films [ 10 ], polymeric hydrophobic and hydrophilic layers [ 11 ]. The main disadvantage of these Bragg stacks is the dependence of their reflectance bands on the direction of incident light, resulting in structural color changes at different viewing angles.…”

“…The change of thickness and/or refractive index of the films (layers) based on zeolite nanocrystals are due to sorption, ion-exchange and capillary condensation of molecules adsorbed in their pores [ 17 , 18 ]. The particular choice of MEL zeolite was made considering their hydrophobicity and high sensitivity towards acetone [ 10 ]. The MEL type zeolite is a pure silica material with three-dimensional channels with a pore opening of 0.53 × 0.54 nm.…”