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Basic Construction of Safety Helmets and Eye and Face Protectors
Published in Katarzyna Majchrzycka, Head, Eye, and Face Personal Protective Equipment, 2020
The most known effect that allows for protective filter optical density changes is a photochromic effect. It is induced by optical radiation of ultraviolet range (UV). As a result of ultraviolet radiation falling on the photochromic material, it darkens; thus its optical density increases. The level of visible radiation transmission passing through a photochromic filter is regulated by ultraviolet radiation (UV) intensity changes occurring in the environments where the filters are used. Photochromic effect is commonly used in the design of spectacles lenses dedicated for ophthalmic optics and in sunglasses filters. It is present for a wide range of the ultraviolet spectrum. Photochromic materials used in ophthalmic optics darken under the influence of ultraviolet radiation of UV-B (280–315 nm) and UV-A (315–400 nm) range existing in the atmosphere. The darkening may also be a result of ultraviolet radiation artificial sources that emit radiation of UV-C range (100–280 mn). An example of a solution where a photochromic effect is used also for ultraviolet radiation range emitted from artificial sources (UV-C) is a design of photochromic automatic welding filter [Pościk 2006].
Organic Field-Effect Transistors for Flexible Electronics Application
Published in Run-Wei Li, Gang Liu, Flexible and Stretchable Electronics, 2019
Jung-Yao Chen, Cheng-Liang Liu
Organic photosensitive material is essential in realizing a flexible photosensitive device. Therefore, the organic photovoltaic material is an appropriate candidate for the charge-transporting material in organic phototransistors. A bulk heterojunction composed of a donor-acceptor system not only provides an effective charge-carrier pathway but also strengthens the photosensitivity through exciton (electron–hole) separation between the junction of donor and acceptor compared to a single component. Photochromic material is a compound that can undergo reversible structural transformations under the influence of light stimuli; this induces a color change, as well as changes in their physical and chemical properties [44]. Through the introduction of photochromic material in the active layer or dielectric layer in an organic phototransistor, the electrical properties can be further verified under light illumination. Besides, the monomer that shows reversible photon-induced polymerization also serves as the photosensitive material in organic phototransistors.
Detectors and Recording Materials
Published in Rajpal S. Sirohi, Optical Methods of Measurement, 2018
Materials that undergo a reversible color change on exposure are called photochromic materials. Photochroism occurs in a variety of materials, both organic and inorganic. Organic photochromics have a limited life and are prone to fatigue. However, organic films of spiropyran derivatives have been used for hologram recording in darkening mode at 633 nm. Inorganic photochromics are either crystals or glasses doped with selected impurities: photochroism is due to a reversible charge transfer between two species of electron traps. Recording in silver halide photochromic glasses has been done in darkening mode at 488 nm and in bleaching mode at 633 nm. Doped crystals of CaF2 and SrO2 have been used in bleaching mode at 633 nm. The sensitivity of photochromics is very low, because the reaction occurs at a molecular level. For the same reason, they are essentially grain-free and have resolution in excess of 3000 lines/mm. Inorganic photochromics have large thicknesses, and hence a number of holograms can be recorded in them. They do not require any processing, and can be reused almost indefinitely. In spite of all these advantages, these materials have limited applications, owing to their low diffraction efficiency (<0.02) and low sensitivity.
Intrinsic structural/morphological and photochromic responses of WO3 co-doped MoO3 nanocomposites based on varied drying methods
Published in Drying Technology, 2021
Onome Ejeromedoghene, Olayinka Oderinde, Fang Yao, Sheriff Adewuyi, Guodong Fu
Photochromic materials are materials with improved optical properties, possess a unique light absorption ability, and can undergo a reversible light-induced color transformation between two forms.[1] These classes of materials have been extensively studied due to their promising potentials in various applications such as ophthalmic lenses, smart windows, optical switches, and other multifunctional devices.[2–5] Although a wide group of photochromic materials have been fabricated from organic precursors, inorganic materials has received serious attention recently because they proffer some improved properties (like thermal stability, strength, chemical resistance, and macroscopic shape molding–thin films, coatings, monoliths, or other suitable forms) over the organic counterparts.[6,7] Besides, inorganic nanocomposite materials based on transition metal oxides (TMO) (e.g., MoO3, WO3, and V2O5) also possess improved photochromic,[8] electrochromic [9–11] and thermochromic [12,13] properties which are widely attributed to the chromogenic coloration as exhibited by these class of nanomaterial.[14,15]
Synthesis and properties of photochromic polymer contain spiro-oxazine induced by ultraviolet light
Published in Soft Materials, 2023
Cheng-Dong Su, Yi-Yuan Shi, Jun Gao
Photochromism,[1] as we know, means that compound A which occurs in a specific chemical reaction is isomerized to compound B under a certain wavelength of light, always accompanied by changes in color. According to the reaction mechanism, organic photochromic small molecules are divided into homolysis and heterolysis of bonds, pericyclic reaction, cis–trans isomerization, and so on. Spiro-oxazine has always been a concern due to its excellent photo-responsiveness. Without UV, SO is in a colorless closed-loop structure and the indole ring is orthogonal to the naphthalene ring, as shown in Scheme 1. Under UV, the bond of C-O in SO is broken. SO is isomerized into photo-merocyanine (PMC) and both the two ring systems are coplanar.
Study of chameleon nylon and polyester fabrics using photochromic ink
Published in The Journal of The Textile Institute, 2018
Subhas Ghosh, Jeanneare Hall, Vikas Joshi
When photochromic dye molecules are exposed to UV light, their molecular structure opens and displays a new color (Billah, Morgan, & Christie, 2008). When the exciting light is removed, the photochromic molecule returns to its original, colorless molecular state. The naphthoxazines are usually preferred compounds to create gray, brown, yellow, and blue colors. Naphthopyrans are benzo-fused chromenes that are used commercially as reversible photochromic compounds. Naphthopyrans undergo a photo-induced ring opening process to the corresponding colored species as illustrated by Kumar, Van Gemert, and Knowles(2000) in Figure 2.