Abstract
Most analyses of phase transformations detected by rare earth ions are based on the luminescence spectrum, while in this study we focus on the luminescence decay processes. We prepared Eu3+-doped (Na, K)0.5Bi0.5TiO3 ceramics and studied their phase structure before and after poling by luminescence spectra, decay curves, and X-ray diffraction (XRD). Luminescence spectra indicated that electric fields induced a transformation in (Na0.8, K0.2)0.5Bi0.497Eu0.003TiO3 (NKBET20) ceramic from tetragonal to rhombohedral phase (R phase). Based on the decay kinetics and the Judd–Ofelt theory, decay curves were shown to identify the fraction of the transformation quantitatively. The data from decay curves suggest that with electric fields increasing from 0 to 50 kV/cm, the R phase fraction increases from about 23 to 89% and the tetragonal phase (T phase) fraction decreases from about 77 to 11%. XRD Rietveld analyses further confirmed the results. In this work, the analyses of the phase fractions are simplified by the monoexponential decay of the pure phases and the biexponential decay of the mixed phase, showing an easy and inexpensive way of studying the phase structures of the materials.
Highlights
Investigations on rare-earth (RE) ions-doped ferroelectric ceramics have attracted significant interest because of the interactions of electrical and luminescence properties [1,2,3]
On the other hand, when RE ions are doped in dilute concentration, they can be utilized as spectroscopic probes to detect phase structures of the hosts [9,10]
The luminescence spectra of NKBET20 ceramics poled under various electric fields are shown in
Summary
Investigations on rare-earth (RE) ions-doped ferroelectric ceramics have attracted significant interest because of the interactions of electrical and luminescence properties [1,2,3]. RE ions doped in ferroelectric materials show efficient emissions, while the excellent electrical properties of the ferroelectric materials could be retained or some improved [4,5]. The phase symmetry of the hosts has important influences on the luminescence properties of doped RE ions, such as crystal-field splitting, luminescence lifetime, and emission efficiency. We focus on the analyses of the luminescence decay curves of Eu3+ ions and use them as tools to probe the phase structure. The optimal electrical performance of ferroelectric ceramics could be realized with multi-phases coexistence like morphotropic phase boundary (MPB) [16,17]. Investigations by X-ray Rietveld analyses correlate well with the presented data from the decay curves analyses
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