Mixed Electrical Conduction of Calcium Aluminates Synthesized by Polymeric Precursors (original) (raw)
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The ionic conductivity of a nanocomposite electrolyte based on calcium-doped ceria/ternary carbonate
2017
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Phase pure monoclinic CaAl 2 O 4 (CA2), CaAl 4 O 7 (CA4) and hexagonal CaAl 12 O 19 (CA12) doped with 1 mol% Ce 3+ phosphor were prepared by combustion method at 500°C in a few minutes. Synthesized phosphor has been well characterized by X-ray diffraction. In the present paper, we discussed the comparative luminescence properties of the phosphors with respect to their crystal structures and the various sites of Ca 2+. This paper provides evidence for different coordinated sites of Ca 2+ ion in the host used. Comparison between calculated and experimental value of position of energy in the lower d-band edge for Ce 3+ ion is discussed. Ce 3+ ions were doped in order to study the emission characteristics in the prepared sample with respect to their crystal symmetry. Different emission spectrum is observed despite of their same crystal structure. The photoluminescence emission spectra of the CaAl 2 O 4 : Ce, CaAl 4 O 7 :Ce, and CaAl 12 O 19 :Ce phosphors show strong Ce 3+ emission at around 370, 330, and 320 nm for the excitation at 300, 273, and 264 nm wavelengths respectively. The emission characteristics are credited to 5d→4f (2 F 5/2 and 2 F 7/2) type transitions in Ce 3+ .
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Eu 2þ doped calcium aluminates, CaAl 2 O 4 :Eu 2þ , were prepared by the Pechini and combustion methods. Very pure monoclinic CaAl 2 O 4 :Eu 2þ was obtained by Pechini method when annealed at 1250°C. The reaction time was shortened but the annealing temperature was the same as that of the conventional solid state method. By using the combustion method, an additional annealing at 900-1100°C was needed to crystallize the initially amorphous material. An unusual hexagonal polymorph was then obtained. The luminescence band of the Pechini prepared CaAl 2 O 4 :Eu 2þ peaking at 440 nm corresponded to that of the solid state prepared material. Persistent luminescence spectrum was the same as that of the UV excited one. The thermoluminescence glow curve position, i.e. the nature of lattice defects was not observed to depend significantly on the preparation method.