Structural, Optical, Luminescence, and Electrical Properties of Eu/Li- and Eu/Na-Codoped Magnesium Bismuth Niobate Pyrochlores

Abstract

Eu-doped bismuth-based Bi1.5 M 0.4Mg0.5Nb1.5O7−δ (M = Li and Na) pyrochlores were synthesized by the organic–inorganic precursor combustion technique. The study examined the effect of rare earth element Eu3+ doping on the structural, dielectric, optical, and luminescence properties of synthesized materials. The analysis showed that the substitution of Bi3+ cations with Eu3+ leads to dielectric permittivity decreasing due to the structural distortion for the Eu-concentrated compositions and low polarizability of Eu3+. The band gap values predicted by electronic band structure calculation using DFT-HSE03 are in line with the experimental ones and tended to increase with the decrease in the unit cell parameters with Eu concentration changing. By the optical and luminescence measurements, the specific roles of Li- and Na-containing host types, additional phases, and dopant concentration in bismuth niobate pyrochlores are shown concerning the dielectric, structural, and Eu3+ emission properties. All Eu-doped bismuth-based pyrochlore ceramics behave as high-frequency dielectrics up to 200 °C and have mixed conductivity (electronic, proton, and oxygen) at T > 200 °C. The obtained dielectric parameters make them suitable for high-frequency ceramic capacitors.

Color-tunable emissions realized by Tb3+ to Eu3+ energy transfer in ZnGdB5O10 under near-UV excitation

“…When monitoring the emission at 612 nm ( 5 D 0 → 7 F 2 transition of Eu 3+ ), the PLE spectra showed a strong broad band, which was due to the charge-transfer (CT) transition between O 2− and Eu 3+ , and a high level of line absorption in the range of 280–470 nm, which was apparently due to the 4f–4f transitions of Eu 3+ . 29,30 Detailed assignments are highlighted in Fig. 4a, where the ground state is 7 F 0 and the excited states includes 5 K 5 (284 nm), 5 F 4 (297 nm), 5 H 6 (316 nm), 5 D 4 (360 nm), 5 L 7 (378 nm), 5 L 6 (393 nm), 5 D 3 (412 nm) and 5 D 2 (463 nm), respectively.…”

Magnocolumbites Mg1–xMxNb2O6−δ (x = 0, 0.1, and 0.2; M = Li and Cu) as New Oxygen Ion Conductors: Theoretical Assessment and Experiment

“…The calculated activation energy E a,σ on the Arrhenius plots of dc conductivity is 0.86–0.88 eV (Table S4 and Figure S7). The n <1 value indicates the translation motion of charge carriers with sudden hopping. , …”

“…The n <1 value indicates the translation motion of charge carriers with sudden hopping. 43,44 In order to explore the electrical transport phenomena in ceramics, frequency dependences of the electrical modulus were analyzed. Starting from 320 °C, the single M″ peak exists on the M″ = f(ν) dependence with a half maximum of 1.14, which indicates that the system is electrically homogeneous (Figure S8).…”