Structural investigation of the A-site vacancy in scheelites and the luminescence behavior of two continuous solid solutions A_1–1.5xEu_x□_0.5xWO₄ and A_0.64–0.5yEu_0.24Li_y□_0.12–0.5yWO₄ (A = Ca, Sr; □ = vacancy)

Abstract

Scheelite compounds with Eu(3+) substitution are well-known red-phosphors. We prepared and performed a detailed structural characterization of A(1-1.5x)Eu(x)□(0.5x)WO4 and A(0.64-0.5y)Eu(0.24)Li(y)□(0.12-0.5y)WO4 (A = Ca, Sr; □ = vacancy) to confirm the A-site vacancy mechanism for charge balance when bivalent A cations were substituted by Eu(3+). All compounds crystallize in I4₁/a with a disordered arrangement of A(2+), Eu(3+), □ at the A-site. The title compounds are all good red phosphors with a high R/O ratio (∼10), indicating that Eu(3+) is located at a significantly distorted cavity. A(1-1.5x)Eu(x)□(0.5x)WO4 shows a saturation phenomenon at a high doping level, x = 0.20. With the incorporation of Li(+), the emission intensity was generally enhanced compared to the Li(+)-free samples, moreover, an increase of the Li(+) content reduces the content of vacancies, resulting in further increase of the luminescence intensity.

Morphology control of uniform CaMoO4microarchitectures and development of white light emitting phosphors by Ln doping (Ln = Dy3+, Eu3+)

“…The unit cell parameters estimated form this XRD pattern were slightly higher than those corresponding to the undoped sample ( when compared with Ca 2+ (1.120 Å). To explain this apparently anomalous behavior, it has to be kept in mind that the heteromorphic substitution of Ca 2+ by Eu 3+ requires charge compensation either by the introduction of Na + (present in the reaction medium coming from the molybdate precursor), 24 by the generation of cationic vacancies 38 or by the introduction of interstitial oxygen. 38 Obviously, all these mechanisms should also influence the unit cell volume, which has been shown to increase in scheelite-type compounds only if cationic vacancies are present.…”

“…To explain this apparently anomalous behavior, it has to be kept in mind that the heteromorphic substitution of Ca 2+ by Eu 3+ requires charge compensation either by the introduction of Na + (present in the reaction medium coming from the molybdate precursor), 24 by the generation of cationic vacancies 38 or by the introduction of interstitial oxygen. 38 Obviously, all these mechanisms should also influence the unit cell volume, which has been shown to increase in scheelite-type compounds only if cationic vacancies are present. 38 Nevertheless, the elucidation of the substitution mechanism operating in our case needs a deeper structural study which will be the subject of a forthcoming paper.…”

“…38 Obviously, all these mechanisms should also influence the unit cell volume, which has been shown to increase in scheelite-type compounds only if cationic vacancies are present. 38 Nevertheless, the elucidation of the substitution mechanism operating in our case needs a deeper structural study which will be the subject of a forthcoming paper.…”

Sheelite-related strontium molybdates: synthesis and characterization

“…The regula-tion of the desired properties of sheelite-related materials can be provided by varying the quantity of the dopant, its nature, the ratios between dopants and the presence of additional vacancies or interstitial positions in the structure. For example, a substitution of A-site ions with Me +3 in ABO 4 complex oxide can be described in two ways: (1) a formation of A 1-x [10][11][12].…”

Host‐Sensitized Photoluminescence and Coordination Environment Evolution in Ba6(Bi1–xTbx)9B79O138 (0 ≤ x ≤ 1)

“…For Eu 3+ ‐doped samples, the intensity ratio of red to orange, (R/O) = I ( 5 D 0 → 7 F 2 )/ I ( 5 D 0 → 7 F 1 ), is usually used as a probe of site symmetry for Eu 3+ 41–45. Generally, a lower symmetry of the crystal field around Eu 3+ leads to a larger R/O ratio 26,32.…”