Browsing by Author "Sullivan, E"

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    Aliovalent M site substitutions of [PO4]3− and [HfO4]4− for [AlO4]5− and [GaO4]5− in the Sr3MO4F-type anti-perovskite oxyfluoride
    (IOP Publishing, 2019-01-17) Keil, ST; Chhoeun, J; Avdeev, M; Sullivan, E
    Rare earth-free phosphor materials have been synthesized via aliovalent doping of [PO4]3− and [HfO4]4− for [AlO4]5− and [GaO4]5− in the Sr3MO4F host lattice (space group I4/mcm). High temperature synthesis was used to synthesize the novel products Sr2.5-xBa0.5Al1-xPxO4F (0.05 ≤ x ≤ 0.15), Sr2.5-xBa0.5Ga1-xPxO4F (0.05 ≤ x ≤ 0.15) and (0.025 ≤ x ≤ 0.075). The structures of these oxyfluorides were analyzed via powder X-ray diffraction (PXRD) and neutron powder diffraction (NPD), and their photoluminescent properties were analyzed through spectrofluorimetry before and after being treated under reducing conditions. Optimal doping was found at a concentration of x = 0.10 for Sr2.5-xBa0.5Al1-xPxO4F (a = 6.8762(4) Å; c = 11.1273(6) Å) resulting in a maximum emission at 454 nm when excited at 214 nm and x = 0.05 for the Ga analog (a = 6.87591(7) Å; c = 11.3722(2) Å) corresponding to an emission centered around 529 nm from excitation with 227 nm. When doping with Hf4+ the optimal concentration for was x = 0.025 (a = 6.8607(1) Å; c = 11.1682(3) Å), resulting in a broad emission between 410–600 nm when excited at 251 nm. © 2019 The Electrochemical Society
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    Designing novel tunable Mn-based inorganic oxyfluoride pigments
    (Elsevier, 2024-06) Lehr, B; Zurowski, G; Chhoeun, J; Kumar, K; Nolis, G; Shanahan, J; Kilpatrick, K; Rojas, K; Cabana, J; Kissel, D; Avdeev, M; Sullivan, E
    A high tunability of green-blue colors in the manganese-doped oxyfluoride Sr2.5A0.5Mn0.1MO4F (A = Ca, Sr, Ba; M = Al, Ga) and anion-deficient Sr2.5A0.5Mn0.1MO4-αF1-δ (A = Ca, Sr, Ba; M = Al, Ga) is reported, and the chromophores responsible for this intense pigmentation are investigated. The hues exhibited by these materials are quantified via diffuse reflectance UV/Vis spectroscopy and measurement of their direct band gaps via Tauc plot. It is shown that choice of A cation (A = Ca, Sr, Ba) and M cation (M = Al, Ga) for as-synthesized phases Sr2.5A0.5Mn0.1MO4F yield a wide range of green colors (band gap range 2.70–2.96 eV). Treatment of these phases under reducing conditions according to Sr2.5A0.5Mn0.1MO4-αF1-δ (A = Ca, Sr, Ba; M = Al, Ga) induces anion non-stoichiometry, shifting the observed colors to a wide range of blue/blue-purple hues (band gaps from 3.31 to 3.66 eV), showing potential as tunable inorganic blue pigments. Density field theory (DFT) calculations support the preferential occupation of the smaller 8-coordinate Sr(2) site by the substituted Mn2+ cation. X-ray absorption near-edge structure (XANES) data reveal more subtle nuances in the interplay between formal manganese oxidation state, crystallographic site and observed hue. In general, for as synthesized (green) Sr2.5A0.5Mn0.1MO4F (A = Ca, Sr, Ba; M = Al, Ga), the edge position in Mn K-edge XANES is consistent with mixed Mn3+-Mn4+ oxidation state whilst a clear pre-edge structure suggesting that Mn is present on a tetrahedral site. This would suggest that during the reduction step, Mn3+/Mn4+ is reduced to entirely Mn2+ and migrates from the tetrahedral to the Sr(2) lattice site. © 2024 Elsevier Ltd. All rights reserved.
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    Structural characterization and photoluminescence in the rare earth-free oxy-fluoride anti-perovskites Sr3−xBi2x/3AlO4F and Sr3−xBi2x/3GaO4F
    (Royal Society of Chemistry, 2017-03-01) Quilty, CD; Avdeev, M; Driskell, JD; Sullivan, E
    The activator Bi3+ has been successfully incorporated into the anti-perovskite oxy-fluoride host lattice Sr3MO4F (M = Al, Ga) to form rare earth-free phosphors of the composition Sr3−xBi2x/3AlO4F, 0 ≤ x ≤ 0.1, and Sr3−xBi2x/3GaO4F, 0 ≤ x ≤ 0.048. These phases absorb in the UV region (λex = 240–326 nm) and exhibit broad emission in the blue region of the visible spectrum (λem = 446.5–455 nm). The optimum compositions for maximum photoluminescent intensity were determined to be Sr2.976Bi0.016AlO4F and Sr2.976Bi0.016GaO4F before concentration quenching occurs. Full structural characterization based upon PXRD and NPD data were performed with DFT calculations suggesting that Bi3+ ions are preferentially incorporated on the ten coordinate Sr(1) site. © The Royal Society of Chemistry 2017
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    Structural distortions in Sr3-xAxMO4F (A=Ca, Ba; M=Al, Ga, In) anti-perovskites and corresponding changes in photoluminescence
    (Elsevier, 2012-10-01) Sullivan, E; Avdeev, M; Vogt, T
    The ordered oxyfluoride family Sr3−xAxMO4F (A=Ca, Ba and M=Al, Ga) has formed the basis of several new inorganic phosphors, and shows great potential for use in phosphor-conversion LED lamp devices. This study examines the correlation between subtle structural changes and photoluminescent behaviour in some of these materials. In order to ascertain whether cation charge compensation has any influence on structure and subsequent photoluminescent behaviour, a comparison was carried out between phases with the nominal compositions Sr2.975Ce0.025AlO4F and Sr2.95Ce0.025Na0.025AlO4F using structural characterisation based upon high-resolution neutron powder diffraction (NPD) data. Additionally, NPD data has been used to elucidate the role of different M cations in these materials, using Sr2.25Ba0.6Eu0.1M0.95In0.05O4−αF1−δ (M=Al, Ga) to determine the effect M cation size has on structure and photoluminescent properties. © 2012, Elsevier Ltd.
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    Structure, stability, and photoluminescence in the anti-perovskites Na3W1−xMoxO4F (0≤x≤1)
    (Elsevier, 2015-10-01) Sullivan, E; Avdeev, M; Blom, DA; Gahrs, CJ; Green, RL; Hamaker, CG; Vogt, T
    Single-phase ordered oxyfluorides Na3WO4F, Na3MoO4F and their mixed members Na3W1−xMoxO4F can be prepared via facile solid state reaction of Na2MO4·2H2O (M=W, Mo) and NaF. Phases produced from incongruent melts are metastable, but lower temperatures allow for a facile one-step synthesis. In polycrystalline samples of Na3W1−xMoxO4F, the presence of Mo stabilizes the structure against decomposition to spinel phases. Photoluminescence studies show that upon excitation with λ=254 nm and λ=365 nm, Na3WO4F and Na3MoO4F exhibit broad emission maxima centered around 485 nm. These materials constitute new members of the family of self-activating ordered oxyfluoride phosphors with anti-perovskite structures which are amenable to doping with emitters such as Eu3+. © 2015 Elsevier Inc.
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    Synthesis and structural characterization of the vividly colored first row transition metal-containing oxyfluoride antiperovskites Sr3-xMnxMO4F and Sr3-xMnxMO4-αF1-δ (M = Al, Ga)
    (Elsevier, 2018-06-01) Quilty, CD; Avdeev, M; Sullivan, E
    Incorporation of dopant amounts of the divalent transition metal cation Mn2+ into the oxyfluoride material Sr3-xMnxMO4F (M  = Al, Ga; 0 ≤ x ≤ 0.1) yields green powders which vary in hue depending on the identity of M. Treatment of these phases with post-synthesis annealing under reducing conditions produces anion deficient phases according to Sr3-xMnxMO4-αF1-δ displaying vivid purple coloration. Intense colors are likely due to small amounts of Mn3+ on the tetrahedral M site. Full structural characterization based upon powder X-ray diffraction (PXRD), neutron powder diffraction (NPD), and thermogravimetric analysis (TGA) data are presented herein, demonstrating that the Sr3-xAxMO4F (A = Ca, Sr, Ba; M = Al, Ga) anti-perovskite structure can readily accommodate first row transition metals. © 2018 Elsevier Ltd.