Sol-Gel Derived Single Layer Zeolite-MgF2 Composite Antireflective Coatings with Improved Mechanical Properties on Polycarbonate

Single layer antireflective coatings with good optical and mechanical properties are difficult to be obtained on temperature sensitive substrates like plastics. This challenge has been taken up in the present study. Single layer MgF2 and for the first time, zeolite 4Å… and zeolite 4Å… - MgF2 composite antireflective coatings were generated by a wet chemical route on flat polycarbonate sheets and characterized for their reflectance, surface roughness, thickness, porosity, surface morphology and scratch hardness by haze measurement. Autoclaving and boiling water treatment under microwave irradiation were used in case of MgF2 sols and zeolite/zeolite-MgF2 coatings respectively. Pure MgF2 coatings deposited after autoclaving of the MgF2 sol yielded a low refractive index of 1.28 and an average reflectance of 1.9% vis-Å -vis 9.7% reflectance for an uncoated polycarbonate substrate over the wavelength range of 400-1100 nm. Single layer zeolite coatings after a brief treatment in boiling water under microwave irradiation yielded a reflectance of 5.1%. A composite zeolite-MgF2 coating exhibited a reflectance of 2.8% and the percentage change in haze after crockmeter testing in case of the composite coating was lower than that of a pure MgF2 coating. This implied that the composite layer had improved mechanical properties combined with good optical properties and could be suitable for practical applications

Nanocontainers for Self-Healing Coatings on Mild Steel

Mild steel is an important material in construction, automobile, and other engineering applications. Long exposure to a corrosive environment causes damage to the material and makes it less efficient for usage. Various methodologies such as barrier coatings and self-healing coatings are employed to prevent corrosion to occur. To increase the performance of the coatings, modifications are carried out by the addition of corrosion inhibitors into the coating matrix. Direct addition leads to unwanted reactions with the coating matrix and loss of corrosion inhibitor itself. In order to prevent this problem, nanocontainers are used to encapsulate the self-healing agent/corrosion inhibitor. Therefore, recent corrosion prevention methods involve the fabrication of multifunctional coatings using different nanocontainers such as halloysite nanotubes, polymeric microcapsules, layered double hydroxide, etc. loaded with corrosion inhibitors. The release of corrosion inhibitors works on trigger mechanism arising due to change in external stimuli and thus increasing the durability of the coatings

Sol–gel derived Ba/SrTiO3–MgF2 solar control coating stack on glass for architectural and automobile applications

Fully dielectric solar control coatings based on alternating layers of Ba (or Sr) TiO3 and MgF2 were deposited on soda lime glass substrates. Three-layered stacks BaTiO3/MgF2/BaTiO3 and SrTiO3/MgF2/SrTiO3 were generated using BaTiO3, SrTiO3 and MgF2 sols deposited on glass using dip coating technique. The multi-layered coating stack was fired at 450oC with different heating rates using a conventional muffle furnace and a conveyorized belt furnace, by which two methods of heat treatment were investigated. Heat treatment after deposition of each layer and a consolidated firing of the three-layered stack with intermediate drying between the layers were carried out and optical properties of the coatings compared. The heat treated coatings were characterized for their UV–Vis–NIR transmittance, microstructure, phase purity, thickness and refractive indices. The coating stack based on BaTiO3 as the high refractive index material in conjunction with MgF2 exhibited better solar control properties than SrTiO3 as the high refractive index material. Moreover, a fast firing of the BaTiO3/MgF2/BaTiO3 stack in a conveyorized belt furnace yielded good NIR blocking and solar control properties, whereas slow firing in a muffle furnace exhibited ~ 80% visible light transmittance with an NIR transmittance of ~ 75%

Оптические свойства многослойных пленочных структур BaTiO3/SiO2,сформированных золь–гель-методом

Золь–гель-методом с последовательной термообработкой синтезированы многослойные пленочные структуры BaTiO3/SiO2 толщиной _ 1 μm, содержащие до 14 пар слоев. Показано, что синтезированные структуры являются рентгеноаморфными. Продемонстрировано формирование в спектрах пропускания и отражения полос, обусловленных интерференционными эффектами. Для более регулярной структуры показано наличие фотонной запрещенной зоны (полосы непрозрачности) в видимом диапазоне с основным минимумом 636 nm с соответствием экстремумов в спектрах пропускания и отражения. Исследованы дисперсионные характеристики пленок титаната бария, различающихся концентрацией исходных золей и продемонстрировано увеличение показателя преломления с увеличением концентрации золя. Для золя с концентрацией 60mg/ml значение показателя преломления составляет 1.88−1.81 в спектральном диапазоне 390−1600 nm. Обсуждаются перспективы золь–гель-технологии формирования структур BaTiO3/SiO2 для нанофотоники и конверторов солнечного излучения

Optical properties of multilayer BaTiO3/SiO2 film structures formed by the sol–gel method

Multi-layer film structures BaTiO3/SiO2 with a thickness of ~1 μm containing up to 14 pairs of layers were synthesized by the sol–gel method with sequential heat treatment. It is shown that the synthesized structures are X-ray amorphous. The formation of bands in the transmission and reflection spectra caused by interference effects is demonstrated. A more regular structure exhibits a photon band gap (opacity band) in the visible range with main minimum at 636 nm and corresponding maximum in the reflection spectra. Dispersion characteristics of barium titanate films with different concentrations of initial sols were studied and an increase in the refractive index with an increase in the concentration of sol was demonstrated. For a sol with a concentration of 60 mg/ml, the refractive index in the spectral range of 390–1600 nm is 1.88–1.81. The prospects of sol–gel technology for the formation of BaTiO3/SiO2 structures for nanophotonics and solar radiation converters are discussed

Upconversion emission from erbium doped sol-gel derived ВаТiOз powders and coatings

Upconversion is a process where light can be emitted with photon energies higher than those of the light generating the excitation (www.rp-photonics.com/upconversion). Diverse inorganic matrices doped with trivalent lanthanides - erbium and holmium exhibit upconversion, transferring infrared light into visible. Thus the effect attracts attention for detection and visualization of infrared radiation. Recently we reported that sol-gel derived barium titanate possessing refractive index about 1.9 in amorphous state can be used as component of optical interference filter in combination with low refractive index films as silica or magnesium fluoride. At the same time room-temperature luminescence of lanthanides in sol-gel derived barium titanate makes the material and method promising for light conversion. In this work we investigate erbium upconversion emission from sol-gel derived BaTiO3 films and powders

Photoactive Properties of Transport Sol-Gel Layers Based on Strontium Titanate for Perovskite Solar Cells

In this work, we have investigated the photocurrent and spectral sensitivity of the silicon/SrTiO3:xNb/perovskite structures. The sol–gel method carried out the deposition of undoped SrTiO3 layers as well as niobium-doped (SrTiO3:Nb) layers at atomic concentrations of 3 and 6% Nb. The perovskite layer, CH3NH3PbI3_xClx, has been deposited by the vacuum co-evaporation technique. The layers have been characterized by scanning electron microscopy and X-ray diffraction measurements. The volt–ampere characteristics and spectral sensitivity of the fabricated samples have been measured under illumination with selective wavelengths of 405, 450, 520, 660, 780, 808, 905, 980, and 1064 nm of laser diodes. We have shown that for different configurations of applied voltage between silicon, SrTiO3:xNb, and CH3NH3PbI3_xClx, the structures are photosensitive ones with a variation of photocurrent from microamperes to milliamperes depending on Nb concentration in SrTiO3, and the highest photocurrent and spectral sensitivity values are observed when a SrTiO3:Nb layer with 3 at.% of Nb is used. A possible application of the proposed structure with a SrTiO3:Nb layer for perovskite solar cells and photodetectors is being discussed