Probing defects and electronic structure of Eu doped t-Mg2B2O5 nanocrystals using X-ray absorption near edge spectroscopy and luminescence techniques. (October 2020)

• Record Type: Journal Article
• Authors: Kumar, Jitender; Sharma, Aditya; Won, Sung Ok; Kumar, Ravi; Chae, Keun Hwa; Kumar, Shalendra; Vij, Ankush
• Is Part Of: Vacuum. Volume 180(2020)
• Publication Date: 2020-10
• Subjects: Mg2B2O5 nanocrystals -- Defects -- X-ray absorption near edge spectroscopy -- Thermoluminescence -- Photoluminescence; Vacuum -- Periodicals; 621.55
• DOI: 10.1016/j.vacuum.2020.109602
• Languages: English
• ISSNs: 0042-207X

Abstract

Abstract: We report here the defects and electronic structure study of Eu (1%, 3%, 5%) doped t- Mg2 B2 O5 nanocrystals synthesized using low temperature combustion method, and probed using x-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray absorption near edge spectra (XANES), photoluminescence (PL) and thermoluminescence (TL). The XRD analysis of all samples shows single phase triclinic crystal structure and average crystallite size decreases with Eu doping in Mg2 B2 O5 . The experimental XANES spectra of each sample acquired at Eu M5, 4 -edges were compared with simulated absorption edges using atomic-multiplet calculations, which clearly shows the presence of Eu 3+ in Mg2 B2 O5 . The O K-edge spectra of Eu doped Mg2 B2 O5 predicts the formation of O and Mg defects upon increasing Eu concentrations. The photoluminescence of Mg2-x Eux B2 O5 nanocrystals at an excitation of 325 nm comprises of a group of sharp peaks owing to intra-4f transitions in Eu 3+ and confirms the lowering of local symmetry with Eu concentration in Mg2 B2 O5 . The effect of Eu doping on the trapping states was probed using TL after irradiating Mg2 B2 O5 with ultra-violet radiations (365 nm), which shows the presence of shallow and deep level trapping states. The corresponding activation energies of trapping states were determined using glow curve deconvolution method based on Kitti's general order equation. Highlights: We synthesized single phase triclinic Eu doped t -Mg2 B2 O5 nanocrystals, for the first time, using combustion method relatively at a much lower temperature than other techniques. HRTEM confirms the nanoparticles formation. The vacancies related defects were investigated using XANES spectra collected at O K edge, while valence state of Eu in Mg2 B2 O5 was probed using XANES at Eu M5, 4 edges which were compared with simulated absorption edges suing atomic multiplet calculations. Thermoluminescence of UV (365 nm) irradiated Eu doped t -Mg2 B2 O5 nanocrystals shows the presence of multiple shallow and deep level trapping sites, whose activation energies were calculated using Kitti's general order equation. The PL emission spectra of samples majorly comprised of sharp peaks corresponding to intra 4f transitions in Eu 3+ levels. The increasing asymmetry ratio confirms the lowering of local symmetry with Eu concentration in Mg2 B2 O5 .