title: Cluster coordination and photoluminescence properties of α-Ag2WO4 microcrystals.
abstract: In this paper, we report our initial research to obtain hexagonal rod-like elongated silver tungstate (α-Ag(2)WO(4)) microcrystals by different methods [sonochemistry (SC), coprecipitation (CP), and conventional hydrothermal (CH)] and to study their cluster coordination and optical properties. These microcrystals were structurally characterized by X-ray diffraction (XRD), Rietveld refinements, Fourier transform infrared (FT-IR), X-ray absorption near-edge structure (XANES), and extended X-ray absorption fine structure (EXAFS) spectroscopies. The shape and average size of these α-Ag(2)WO(4) microcrystals were observed by field-emission scanning electron microscopy (FE-SEM). The optical properties of these microcrystals were investigated by ultraviolet-visible (UV-vis) spectroscopy and photoluminescence (PL) measurements. XRD patterns and Rietveld refinement data confirmed that α-Ag(2)WO(4) microcrystals have an orthorhombic structure. FT-IR spectra exhibited four IR-active modes in a range from 250 to 1000 cm(-1). XANES spectra at the W L(3)-edge showed distorted octahedral [WO(6)] clusters in the lattice, while EXAFS analyses confirmed that W atoms are coordinated by six O atoms. FE-SEM images suggest that the α-Ag(2)WO(4) microcrystals grow by aggregation and the Ostwald ripening process. PL properties of α-Ag(2)WO(4) microcrystals decrease with an increase in the optical band-gap values (3.19-3.23 eV). Finally, we observed that large hexagonal rod-like α-Ag(2)WO(4) microcrystals prepared by the SC method exhibited a major PL emission intensity relative to α-Ag(2)WO(4) microcrystals prepared by the CP and CH methods.
authors.affiliation: Universidade Estadual Paulista, P.O. Box 355, CEP, 14801-907 Araraquara, São Paulo, Brazil. laeciosc@bol.com.br
authors.forename: L S
authors.initials: LS
authors.lastname: Cavalcante
authors.forename: M A P
authors.initials: MA
authors.lastname: Almeida
authors.forename: W
authors.initials: W
authors.lastname: Avansi
authors.forename: R L
authors.initials: RL
authors.lastname: Tranquilin
authors.forename: E
authors.initials: E
authors.lastname: Longo
authors.forename: N C
authors.initials: NC
authors.lastname: Batista
authors.forename: V R
authors.initials: VR
authors.lastname: Mastelaro
authors.forename: M Siu
authors.initials: MS
authors.lastname: Li