Correlation between Raman spectra and color of tungsten trioxide (WO3) thermally evaporated from a tungsten filament

Abstract

The color exhibited by tungsten trioxide (WO3) can be associated with both its stoichiometry and crystallinity. Correlation between the color exhibited by WO3 powders and their purity and crystalline properties is reported in this paper. The WO3 powders were deposited by evaporation of tungsten trioxide from the surface of a tungsten filament. The WO3 powders exhibited three different shades of blue: navy, royal, and sky. The color of the WO3 powders changed to white after thermal treatment at 500 °C for 30 min in an ambient atmosphere. Raman analyses showed that transition from amorphous to crystalline WO3 started when the powders exhibited navy-blue color and ended when WO3 powders exhibited a white color. Scanning electron microscopy analysis showed particle agglomeration characteristics in all WO3 powders, even after they were thermally treated. The mechanism of deposition of WO3 from the tungsten filament was suggested to be governed by thermal evaporation of tungsten trioxide from the surface of the oxidized tungsten filament.

Surface-Ligand-Controlled Enhancement of Carrier Density in Plasmonic Tungsten Oxide Nanocrystals: Spectroscopic Observation of Trap-State Passivation via Multidentate Metal Phosphonate Bonding

“…56−60 The Raman stretch at 318 cm −1 can also be attributed to a monoclinic bending mode. 56 The Raman vibrations appear to be broader and shifted to lower wavenumbers as compared to the tungsten oxide films and larger structures. 58,61 This is due to the distortion in the overall crystal lattice resulting from oxygen vacancies that reduces the crystallinity compared to larger bulk-like structures.…”

“…The Raman spectrum of as-synthesized NPLs includes distinct monoclinic tungsten oxide vibrational modes (Figure B, black line). These peaks are assigned as the crystal lattice vibration of (W 2 O 2 ) n chains at 71 cm –1 , W–O stretch at 123 cm –1 , bending vibration of (O–W–O) at 252 cm –1 , and (O–W–O) stretches of the WO 6 octahedra at 692 and 797 cm –1 . − The Raman stretch at 318 cm –1 can also be attributed to a monoclinic bending mode . The Raman vibrations appear to be broader and shifted to lower wavenumbers as compared to the tungsten oxide films and larger structures. , This is due to the distortion in the overall crystal lattice resulting from oxygen vacancies that reduces the crystallinity compared to larger bulk-like structures .…”

“…Moreover, local assembly of the sample may also influence the Raman response by the presence of TDPA due to differences in the organic ligand attachment onto the solid inorganic surface . Finally, increases in oxygen vacancy and the presence of a high density of free carriers could shift the Raman vibrational modes to lower wavenumbers, , particularly the appearance of Raman stretches at 252 and 692 cm –1 that resemble in highly oxygen deficient W 18 O 49 nanomaterials . Nevertheless, the above-mentioned XRD and spectroscopic characterizations invalidate the possibility of alteration in the crystal structure of WO 3– x NPLs upon TDPA treatment and rather support the concept of the variation in N e values.…”

Inorganic–Organic Interfacial Electronic Effects in Ligand-Passivated WO3–x Nanoplatelets Induce Tunable Plasmonic Properties for Smart Windows

“…Structural analysis by Raman provides similar results indicating no change in ligand treatment (Figure C). All ligand-treated samples contain characteristic oxygen-deficient crystal lattice vibration-related peaks, marked by dashed lines at 803, 668, and 233 cm –1 . − Raman spectroscopy is known to be sensitive to subtle surface binding changes and the position of Raman vibrational stretches could vary depending on the sampling deposition technique. As illustrated in Figure C, depending on the type of ligand used to passivate the surface of WO 3– x NPLs, we observe a slight shift in the peak position in Raman spectra, which can be attributed to the changes in the film morphology, as well as electronic interactions between ligands and NPLs. , As described above, we showed that phosphonate and carboxylate binding head groups form different bonding interactions with WO 3– x NPLs.…”

Nano-Structuration of WO3 Nanoleaves by Localized Hydrolysis of an Organometallic Zn Precursor: Application to Photocatalytic NO2 Abatement

“…of Zn(Cy) 2 to the yellow suspension of WO 3 •2H 2 O in toluene, it quickly turns green, indicating the reaction of the zinc precursor with the NLs. The color change is ascribed to the formation of W n+ (n < 6) species associated with the presence of oxygen vacancies [35,36]. This suggests that the oxophilicity of Zn 2+ ions of the precursor is strong enough to remove oxygen atoms from the WO 3 lattice and yield the first surface germs of ZnO.…”