Properties Of Rare-Earth Doped Bi₃TiNbO₉:Tb³⁺/Yb³⁺ Ceramics

In recent years, the family of bismuth layer-structured ferroelectrics (BLSFs) has attracted much attention for their potential use in high temperature piezoelectric devices and ferroelectric random access memories (FeRAMs), because of their relatively high Curie point and excellent fatigue endurance property, respectively. Bi₃TiNbO₉ (BTN) is one of the BLSF compounds, it have very high TC (940℃). Up to now, most of the studies about BTN have concentrated on the crystal structure, the properties of pure bulk ceramics and its intergrowth compounds. This article mainly concentrated on the ferroelectric, piezoelectric and upconversion luminescence properties of the rare-earth-ion Tb³⁺ and Yb³⁺ co-doped BTN ceramics.First, upconversion emissions were studied in order to expand the optical properties of ferroelectric ceramics. The luminescence properties and energy transfer mechanisms were found based on analyses of fluorescence spectroscopy and pump power dependence. Upconversion emissions were observed in Tb³⁺/Yb³⁺ co-doped BTN ceramics under diode laser excitation of 980nm. The spectra consist of ⁵D₄â†'⁷F₆, ⁵D₄â†'⁷F₅ and ⁵D₄â†'⁷F₂ transitions, which came from Tb³⁺ ion. Green upconversion emissions which are attributed to ⁵D₄â†'⁷F₅ transition were strongest. Pump power dependence investigations indicate that upconversion emissions arise from second-photon processes. Decay profiles investigations indicate that upcon-version emissions have lifetime withμs.Further, poling effect on the piezoelectric, ferroelectric and upconversion luminescence properties were studied. The piezoelectric coefficient d₃₃ and the electromechanical coupling coefficient of radial vibration kp were almost equal between rare-earth co-doped and pure ceramics. In addition, hysteresis loops investigations indicate that, with the polarization voltage increases, the remanent polarization and loop area decreased. Upconversion luminescence observations indicate that integral intensity of fluorescence changed when the polarization voltage changes, this phenomenon provide a experimental evidence to the one idea which hope that application of fluorescent probes to study the polarization state of ferroelectrics.