EFFECT OF HOLMIUM DOPING ON STRUCTURAL AND LUMINESCENCE PROPERTIES OF BaBi2Nb2O9 FERROELECTRIC CERAMICS

Abstract

This study presents a comparative investigation of BaBi₂₋yNb₂HoyO₉ ceramics doped with varying concentrations of holmium (y = 0.00 to 0.08). The materials were developed via solid state synthesis route. This study investigates the structural, optical, electrical, and luminescent properties of pure and Ho³⁺-doped BaBi₂Nb₂O₉ ceramics. X-ray diffraction (XRD), photoluminescence (PL), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible (UV-Vis) spectroscopy, and ferroelectric (PE loop) measurements were used for comprehensive characterization. The XRD pattern indicated the presence of a single-phase orthorhombic structure and no other secondary phase was found. SEM micrographs revealed a plate-like, randomly oriented microstructure with non-uniform grain distribution. PL spectra under 455 nm excitation exhibited enhanced emission intensity in Ho-doped samples, confirming the effective luminescence contribution of Ho³⁺ ions. FTIR spectra showed distinct vibrational bands near 422, 614, and 828 cm⁻¹ corresponding to metal-oxygen bond stretching and bending modes, indicating the presence of NbO₆ octahedra and Bi–O linkages. Shifts in these peaks with increasing Ho content suggest successful incorporation of Ho³⁺ into the lattice and induced structural distortions. UV-Vis reflectance spectra revealed a reduction in reflectance with Ho doping and a redshift in the absorption edge, implying a slight decrease in optical band gap energy, possibly due to the introduction of intermediate energy states by Ho³⁺ ions. The PE loop measurements displayed unsaturated and slim hysteresis loops for all samples, with maximum polarization observed at y = 0.04, indicating improved ferroelectric response at this doping level. The vii degradation of ferroelectric behavior at higher doping concentrations (y = 0.06 and 0.08) can be attributed to increased defect density and structural disorder. These findings demonstrate that Ho³⁺ doping induces significant modifications in structural, optical, and electrical behaviour, making these ceramics promising candidates for multifunctional applications in optoelectronics and memory devices.