Photochromism in transition-metal oxides

Abstract

Transition-metal oxides -including tungsten oxide, molybdenum oxide, titanium dioxide, vanadium pentoxide, niobium pentoxide and zinc oxide -exhibit photochromism upon bandgap excitation. These oxides constitute an important group of inorganic chromogenic materials, which is of great significance in the perspective of science and technology. During the past several decades, great progresses have been made in the microstructure, photochromic behavior and mechanism of these oxides, specifically of tungsten oxide. These studies underscore the opportunity of using these materials in photonic applications. The details will be presented in this review.

Characterization of the reversible photoinduced optical changes in Sb-based glasses

“…Electrochromic and photochromic materials containing tungsten compounds have been studied in amorphous and crystalline thin films [14,15]. The photochromic changes in such films were promoted by the incidence of pulsed or CW lasers in the UV region of the spectra.…”

“…Considering that during the preparation of the glasses, defects can be formed due to the quenching process, oxygen vacancies can be expected to be present inside the glassy structure. Therefore, the same mechanism proposed elsewhere [15] could only be assumed, replacing hydrogen or lithium by antimony, as follows:…”

“…Extensive attention also has been paid to photosensitive thin films based mainly in both amorphous and crystalline WO 3 and MoO 3 [4][5][6][7]. These materials can exhibit changes of color after exposure to UV laser light.…”

“…These materials can exhibit changes of color after exposure to UV laser light. One of the hypotheses for this behavior is that upon bandgap irradiation, electron-hole pairs may be generated [5]. In the case of tungsten oxide-based materials, the photon-generated free electrons and holes take part in the formation of substoichiometric WO 3 (containing both W +6 and W +5 oxidation states) leading to color changes.…”

“…In the case of tungsten oxide-based materials, the photon-generated free electrons and holes take part in the formation of substoichiometric WO 3 (containing both W +6 and W +5 oxidation states) leading to color changes. The bandgap of W-based films ranges from 480 to 365 nm [5] depending on the preparation conditions. As discussed above, electron-hole pairs need to be present for the observation of color changes, and their formation is typically achieved by, for example, exposing the films to a 308 nm XeCl excimer pulsed laser (with an energy density of about 3.9 · 10 6 W cm À2 ) [4] or to a pulsed 355-nm Nd-YAG laser [6].…”