Nanoparticles (NPs) of WO3-x Compounds by Polyol Route with Enhanced Photochromic Properties

Abstract

Tungsten trioxide (WO3) is well-known as one of the most promising chromogenic compounds. It has a drastic change of coloration induced from different external stimuli and so its applications are developed as gas sensors, electrochromic panels or photochromic sensors. This paper focuses on the photochromic properties of nanoWO3, with tunable composition (with tunable oxygen sub-stoichiometry). Three reference samples with yellow, blue and black colors were prepared from polyol synthesis followed by post annealing under air, none post-annealing treatment, or a post-annealing under argon atmosphere. These three samples differ in terms of crystallographic structure (cubic system versus monoclinic system), oxygen vacancy concentration, electronic band diagram with occurrence of free or trapped electrons and their photochromic behavior. Constituting one main finding, it is shown that the photochromic behavior is highly dependent on the compound’s composition/color. Rapid and important change of coloration under UV (ultraviolet) irradiation was evidenced especially on the blue compound, i.e., the photochromic coloring efficiency of this compound in terms of contrast between bleached and colored phase, as the kinetic aspect is high. The photochromism is reversible in a few hours. This hence opens a new window for the use of tungsten oxide as smart photochromic compounds.

Effect of the Ammonium Tungsten Precursor Solution with the Modification of Glycerol on Wide Band Gap WO3 Thin Film and Its Electrochromic Properties

“…10 of 13 Q = I dt (4) In the formula, ∆OD is the optical density of the change between two optical states at 680 nm wavelength; T b and T c were defined above; the injecting and extracting charge density (Q) were calculated by integrating the current of a cycle of the electrochromic test; A is the electrochromic total area. The coloration efficiency (CE) value of sample was calculated to be 46.3 cm 2 •C −1 for WO 3 thin films annealed at 400 • C in this work, as shown in Figure 8b.…”

“…It is worth mentioning that it is the transition metal oxides that are the fascinating semiconducting materials which possess a variety of properties, applications and functions [2]. Tungsten trioxide (WO 3 ), the most widely studied and used electrochromic material, has been studied for many years since having been found by Deb in the 1960s, thanks to its attractive characteristics of high coloring efficiency, good optical modulation ability and decent chemical stability in the field of electrochromism [3][4][5][6]. It is remarkable that WO 3 with various crystalline structures by different synthesis methods is extensively appropriate for diverse device applications [7][8][9], such as the electrochromic smart window [10,11], rear-view automatic-dimming rearview mirror [12], gas sensor device [13][14][15], and military camouflage [16], etc.…”

WO3 Inversce Opal Photonic Crystals: Unique Property, Synthetic Methods and Extensive Application

“…Especially, the unit‐cell parameters can vary as 7.32 Å, 7.56 Å and 7.73 Å, with the different angle along crystallographic axes. [ 25 ] And WO 3 IOPCs owns an ordered porous structure, which is formed by periodically arranged electromagnetic mediums of WO 3 and voids. [ 26 ] This unique morphological structure can endow WO 3 IOPCs with great optical and electrical property.…”

Improvement of the photochromism taking place on ZnO/MoO3 combined material interfaces

“…For illustration, changing the synthesis route induces a modification of the morphology for the home-made metal oxide in such a way that the contact areas between the two compounds can be greatly tuned. The surface chemistry can be impacted, the polyol route leading to the reductive behaviour of the polyol solvent to oxygen-deficient surfaces for metal oxides [38][39][40] . In turn, the defect surfaces act like intrinsic n-type defects and are associated with the occurrence ARTICLE Journal Name…”