Structural Properties, Photoluminescence, and Judd-Ofelt Parameters of Eu3+- Doped CoNb2O6 Phosphor

Abstract

Trivalent Eu-activated CoNb2O6 phosphors were fabricated using the molten salt method, which provides enhanced homogeneity and low sintering temperature. The ceramic samples were examined by spectral and structural analyses. In X-ray diffractions, the single phase of orthorhombic columbite type CoNb2O6 structure was obtained for 0.5-10 mol% Eu3+ doping concentrations, while a two theta peak shift towards the smaller angles occurred. SEM examinations show an irregular morphology and sub-micron grain sizes. In photoluminescence (PL) spectra, the phosphors showed typical Eu3+ emissions with the 5F0 → 7FJ (J=0, 1, 2, 3, 4) transitions, and high emission peaks were observed at the 5D0 → 7F2 transition. The photoluminescence of CoNb2O6:Eu3+ decreased over 5 mol% because of the concentration quenching. The energy transfer mechanism and critical distance of the phosphor are the dipole-dipole (d–d) interaction, and 15.70 Å, respectively. The spectral features of the phosphors were assessed by calculating the Judd-Ofelt intensity parameters (Ω2, Ω4) from the PL emission spectrum. The low Ω2 parameter values or/and the Ω4>Ω2 trend for CoNb2O6:Eu3+ phosphors were related to the less covalent or more ionic character of the Eu3+–O2˗ bond and the high local symmetry of the Eu3+ sites, while the high Ω4 parameter values may be ascribed to the decrease in the electron density in the ligands.

Structural and dielectric properties of Eu3+,B3+ co-doped CoNb2O6 ceramic

“…Also, as seen in SEM micrographs in Figure 4(a-e), increasing Eu 3+ concentration promotes the formation of collapses and holes in the grains. Moreover, it has been previously reported that the grain sizes of powder samples produced by the molten salt method at 800 °C are in the range of 0.05-2 m (20). However, in this study, boron was subsequently added and the temperature was increased to 900 °C after pelletization.…”

“…The MNb2O6 structure has a significant advantage in that it can host guest ions with ionic sizes comparable to the Nb and divalent M 2+ ions found in the structure. As MNb2O6 structure, cobalt niobate (CoNb2O6) has been studied due to its magnetic (13)(14)(15)(16), neutron scattering (17), luminescence (18)(19)(20)(21), dielectric (22,23) gas sensing (24,25) and magnetic-thermodynamic (26,27) properties. Singh et al (22) reported the dielectric and ferroelectric properties of Ti 4+ doped CoNb2O6…”