WO₃·nH₂O Crystals with Controllable Morphology/Phase and Their Optical Absorption Properties

Abstract

In this work, a one-step hydrothermal route is developed to prepare WO3·nH2O crystals with various morphology/phases, for which any surfactants, templates, or structure-directing agents are not used. Five types of WO3·nH2O crystals, including o-WO3·H2O nanoplates, rectangular m-WO3 nanosheets, o-WO3·0.33H2O microspheres, h-WO3 nanorods, and bundle-like h-WO3 hierarchical structures, are successfully obtained by adjusting the amount of H2SO4 and reaction temperature. According to the experimental results, the formation mechanism for various WO3·nH2O species is proposed. In addition, the optical absorption properties of these WO3·nH2O crystals are also investigated by UV–vis absorption spectra.

Effects of Size and Morphology on the Excited-State Properties of Nanoscale WO3 Materials from First-Principles Calculations: Implications for Optoelectronic Devices

“…In spite of this, the calculated absorption edge energies for these NP families (cubic and rectangular) were in fair agreement with the ones reported for hydrated WO 3 nanoplates (550 nm). , For the spherical NPs, these systems showed a similar evolution of the spectra with the size as the cubic family, with the n = 19 and n = 32, n = 80, n = 147, and n = 281 reproducing the experimental absorption features for the small, medium, and large QDs, respectively. However, in this case, the absorption thresholds achieved by larger nanostructures converged with respect to their size to an energy of 455 nm, thus showing a good match with the experimental values with a small over- and underestimation (0.1 eV) of the bulk and microsphere NP gaps, respectively. More importantly, our calculations fairly reproduced the band gap expansion of about 0.4 eV observed experimentally when moving from cubic-like to spherical large NPs .…”

“…However, in this case, the absorption thresholds achieved by larger nanostructures converged with respect to their size to an energy of 455 nm, thus showing a good match with the experimental values with a small over- and underestimation (0.1 eV) of the bulk and microsphere NP gaps, respectively. More importantly, our calculations fairly reproduced the band gap expansion of about 0.4 eV observed experimentally when moving from cubic-like to spherical large NPs . In a similar way, the GW /BSE simulated spectrum of the monoclinic bulk phase showed an absorption threshold around 400 nm (see Figure S4 in the Supporting Information), which yielded to an overestimation of the experimental optical gap by 0.5 eV.…”

“…More importantly, our calculations fairly reproduced the band gap expansion of about 0.4 eV observed experimentally when moving from cubic-like to spherical large NPs. 27 In a similar way, the GW/BSE simulated spectrum of the monoclinic bulk phase showed an absorption threshold around 400 nm (see Figure S4 in the Supporting Information), which yielded to an overestimation of the experimental optical gap by 0.5 eV. A similar overestimation of the electronic gaps computed at the GW level has been reported previously for the bulk phase.…”

“…27,61 For the spherical NPs, these systems showed a similar evolution of the spectra with the size as the cubic family, with the n = 19 and n = 32, n = 80, n = 147, and n = 281 reproducing the experimental absorption features for the small, medium, and large QDs, respectively. However, in this case, the absorption thresholds achieved by larger nanostructures converged with respect to their size to an energy of 455 nm, thus showing a good match with the experimental values with a small overand underestimation (0.1 eV) of the bulk 17 and microsphere NP 27 gaps, respectively. More importantly, our calculations fairly reproduced the band gap expansion of about 0.4 eV observed experimentally when moving from cubic-like to spherical large NPs.…”

“…An additional factor affecting the optical absorption features of WO 3 nanomaterials is the morphology, as it was evidenced by Liao et al, demonstrating that the absorption edge of these materials can be finely tuned in a range of 2.3−2.9 eV by modifying the shape of the NP (nanoplates, rectangular nanosheet, microspheres, or hexagonal nanowires and bundles). 27 We can thus conclude that the rationalization of the role played by quantum confinement and morphological effects in the absorption and emission properties of WO 3 nanostructures will definitively help toward their technological exploitation.…”