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Electronic structure and luminescence assets in white-light emitting Ca₂V₂O₇, Sr₂V₂O₇ and Ba₂V₂O₇ pyro-vanadates: X-ray absorption spectroscopy investigations

Author:
Sharma, Aditya, Varshney, Mayora, Chae, Keun-Hwa, Won, Sung Ok
Source:
RSC advances 2018 v.8 no.46 pp. 26423-26431
ISSN:
2046-2069
Subject:
Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray absorption spectroscopy, X-ray diffraction, absorption, annealing, assets, barium, calcium, chemical precipitation, crystal structure, energy, geometry, metal ions, optical properties, photoluminescence, rare earth elements, scanning electron microscopy, strontium, white light
Abstract:
Ca₂V₂O₇, Sr₂V₂O₇, and Ba₂V₂O₇ pyro-vanadates were synthesized using a modified chemical precipitation method and annealing. Detailed crystal structure, morphology, electronic structure and optical properties were investigated by XRD, UV-visible absorption, FTIR, Raman, FE-SEM, XANES, and photoluminescence spectroscopy. Rietveld refinement on the XRD patterns of Ca₂V₂O₇, Sr₂V₂O₇, and Ba₂V₂O₇ has confirmed the triclinic structure (space group; P1̄(2)) of the pyro-vanadates. The band gap energy of Ca₂V₂O₇, Sr₂V₂O₇, and Ba₂V₂O₇ is estimated to be ∼2.67 eV, ∼2.97 eV and ∼3.09 eV, respectively. XANES spectra at the Ca L-edge, Sr K-edge and Ba L-edge have confirmed the Ca²⁺, Sr²⁺ and Ba²⁺ ions in the Ca₂V₂O₇, Sr₂V₂O₇ and Ba₂V₂O₇ compounds, respectively. V K-edge XANES spectra have strengthened the presence of sub-pentavalent V ions in all of the pyro-vanadates. O K-edge XANES spectra of Ca₂V₂O₇, Sr₂V₂O₇ and Ba₂V₂O₇ have shown dominating tetrahedral symmetry of the V ions which is also corroborated with the V K-edge XANES. Broad-band emission spectra, ranging from 400 nm to 700 nm, have been observed from the charge-transfer transitions of VO₄ tetrahedra. ³T₁ → ¹A₁ and ³T₂ → ¹A₁ transitions, from the VO₄ tetrahedra, have provided two distinct emission peaks from the compounds which exhibit a red-shift with the decreasing ionic-radii of alkali-earth metal ions. The mixed compounds, with equal weight proportions, have shown remarkable emission characteristics towards the realization of rare-earth element free white-light-emitting devices.
Agid:
6185947