Investigation Of Upconversion Luminescence Property Of Bi_3-x RE_xTiNbO₉ Ceramic

Bismuth layer-strutured ferroelectrics(BLSF), also known as Aurivillius phase, usually possessing high Curie temperature and good anti-fatigue properties. BLSF are being investigated because of their interesting ferroelectric and piezoelectric, optical and dielectric behaviors and so on. These compounds play an important role in the integrated ferroelectrics industry. Recently upconversion (UC) in rare-earth (RE) ion-doped this kind of materials has been intensively studied. Bismuth titanate niobate (Bi₃TiNbO₉), an interesting member of BLSF family. There are two (BiTiNbO₇)^2-layers between two Bi₂O₃ layers. Bi₃TiNbO₉ is one of the promising candidates for high temperature piezoelectric applications because of its very high Tc (940℃), a large number of researchers have conducted in-depth research. But optical spectroscopy of Er-Yb ions co-doped Bi₃TiNbO₉ and the connection between the polarization and luminescent behavior are less studied. This article will mainly discuss this problem.In this paper, the Er-Yb co-doped Bi₃TiNbO₉ ceramics (Bi_2.93Er_0.02Yb_0.05TiNbO₉) is prepared by a conventional solid-state reaction technique with different of sintering temperature and bismuth content. We have been studied the effects of sintering temperature and bismuth content on upconversion luminescence properties. And the upconversion process of Er-Yb co-doped Bi₃TiNbO₉ ceramics is two-photon process by fitting the energy dependence of photoluminescence. We have been characterized the electrical properties of ceramic samples and found that the remanent polarization (2Pr) values has increased by 70% after polarized. The photoluminescence (PL) of the Er-Yb co-doped Bi₃TiNbO₉ ceramics was studied in detail with the samples poled or unpoled, in order to study the poling effect on the luminescent properties of Er-Yb ions in the ferroelectric ceramics. Comparing with the unpoled sample, photoluminescence intensity of the poled ceramic obviously increace. The mechanism of polarization affecting the upconversion luminescence properties of ceramic is mainly the polarization changes the environment of rare earth ions, and a local electric field around the rare earth ions has produced, and finally the crystal field in luminescence center of the rare earth ion has changed; crystal field has mixed the crystal symmetry group which belongs to the same irreducible representation but different total angular momentum (J) has weaken the selection rules and the transition probability increases, so that upconversion luminescence emission enhances. With the increasing of polarization voltage, the environmental changes around the rare earth ions increased. And then the upconversion luminescence intensity of ceramic samples enhanced.As the upconversion luminesrsion intensity can be adjusted by the polarization. We hope that the upconversion luminescence can be used to characterize the polarization state of ferroelectrics and detect the polarity.