Effect Of Polarization And Phase-transitions On The Photoluminescence Properties Of Pr³⁺-doped (Ba_0.77Ca_0.23)TiO₃ Ceramics

Recently,oxide-based phosphors are known to be as the potential choice for flat panel display due to the advantage of high chemical stability comparing with the sulfide phosphors when impacted by electrons.Among them,Pr-doped ATiO₃(A=Ca,Sr,Ba)has attracted interests as one kind of the promising oxide-based phosphors for low-voltage field emission display.It is well-known that BaTiO₃,CaTiO₃ and SrTiO₃ are three typical dielectric and ferroelectric materials.Their solid solutions have been and continue to be of interest for investigation,not only because of their various applications,but also for their interesting dielectric and ferroelectric behaviors.However,the research of the probing for the phase transitions and the connection between the polarization and luminescent behavior in some Pr-doped(Ba,Ca,Sr)TiO₃ solid solutions are lack in the open literature.In this study,the photoluminescence of the Pr doped(Ba_0.77Ca_0.23)TiO₃ ceramics was studied in detail under different temperatures with the samples poled or unpoled,in an attempt to probe the phase transitions and to study the poling effect on the dielectric, ferroelectric and luminescent properties of Pr³⁺ions in the ferroelectric ceramics.Firstly, we investigated the temperature dependence of the PL spectra of Pr³⁺doped (Ba_0.77Ca_0.23)TiO₃ ceramics where Pr³⁺ions occupied the Ca²⁺site.Specifically,the PL spectra of the unpoled and poled samples were compared in order to explore the effect of polarization on the luminescence.Comparing with the unpoled sample,all the red emission under the different temperatures of 50 to 300 K increased about 30%for the poled 0.1 mol%Pr³⁺doped ceramic.The polarization leads to the change in peak intensity as well as in spectral shape for the Pr³⁺red emission,while leaves the blue emission unchanged. Secondly,the relationship of the phase transitions and the PL spectra of Pr³⁺doped (Ba_0.77Ca_0.23)TiO₃ ceramics have been studied.The PL spectra are also sensitive to the phase transitions of the ceramic.Obvious peaks for red and blue emission were found around 100 K,corresponding to the tetragonal-orthorhombic transition of the ceramic,and a step decrease in the red emission intensity occurs around the tetragonal-cubic transition. Both the polarization and phase transition effects on the Pr³⁺PL were ascribed to the local environmental changes of Pr³⁺ions in(Ba_0.77Ca_0.23)TiO₃ ceramic.On one hand,the polarization arising from the ferroelectricity of the ceramic can tune the red emission of Pr³⁺ions up to 30%at or below the room temperature.On the other hand,the emission from the Pr³⁺ions can used to be an effective structural probe for testing the phase transitions of the ceramic.