The Effect Of Phase Transition Of Barium Titanate Ferroelectric Ceramics On The Fluorescence Properties Of Doped Rare Earth Ions

Ferroelectric materials play an important role in the fields of medicine,acoustics,machinery,electronics and so on because of their adjustable spontaneous polarization of electric field and the ability of mutual conversion between mechanical energy and electrical energy.Phase transition involves spontaneous polarization,lattice structure,domain wall and so on.The structural phase transition of ferroelectric materials is generally characterized by the temperature dependence of relative dielectric constants.However,the research on the field induced phase transition of ferroelectric materials and the boundary effect of ferroelectric thin films has limitations.It is necessary to develop a fast,contactless,nondestructive,in-situ and spatially resolved method to detect the phase transition of ferroelectric materials.In this paper,Li⁺and Er³⁺were co-doped in BaTiO₃ ceramics and Ba CaTiO₃ ceramics,and Li⁺was introduced to improve the luminescence efficiency of Er³⁺,so as to realize the fine characterization of the phase transition process of ferroelectric materials by fluorescence method.Li⁺and Er³⁺co-doped BaTiO₃ ceramics were synthesized by sol-gel method.The effects of doping elements on the electrical and optical properties of BaTiO₃ based ceramics were systematically investigated.It is found that the introduction of Li⁺can greatly improve the luminous efficiency of Er³⁺in BaTiO₃ ceramics,and improve the ferroelectric and piezoelectric properties of BaTiO₃ ceramics.Through the spectra of²H_11/2,⁴S_3/2and ⁴I_13/2 energy levels of Er³⁺,the corresponding effects of fluorescence characteristics on BaTiO₃ phase transition are studied.It is found that the overall fluorescence intensity,single point luminescence intensity and fluorescence intensity ratio of different energy levels are abnormal near the phase transition temperature,and all changes occur at 126-130℃.The relative change rate of physical quantity(R_CR)was established to characterize the response intensity of different optical parameters to the phase transition of BaTiO₃ ceramics.It was found that the luminescence intensity at 527 nm had the strongest response to the phase transition.The phase transition of Li⁺and Er³⁺co-doped BaTiO₃ in multiple phase transition regions was characterized by the down conversion infrared fluorescence intensity of ⁴I_13/2 energy levels of Er³⁺.By measuring the fluorescence lifetime and excitation spectrum of ⁴I_13/2 and ⁴I_11/2 energy levels of Er³⁺,combined with the derivation of rare earth luminescence rate equation,it is proved that the change of spectral intensity during phase transition is caused by the change of radiation transition probability of ⁴I_13/2 level.It lays a solid foundation for further understanding the relationship between photoluminescence characteristics and phase structure of ferroelectric materials,and further expands the application potential of fluorescence methods in more fields.A method to quantitatively characterize the fine phase transition processes of Li⁺and Er³⁺co-doped BaTiO₃ by observing fluorescence wavelength shift was proposed.The down-conversion infrared fluorescence spectra of the ⁴I_13/2 energy level were measured as a function of temperature.The three structural phase transition processes,namely rhombohedral–orthorhombic,orthorhombic–tetragonal,and tetragonal–cubic transformations,determined by X-ray diffraction results are accompanied by corresponding changes in the position of the fluorescence peaks,having an exact consistency.This contactless,non-destructive and spatially-resolved fluorescence method provides a local quantitative analysis for the phase transition processes of Li⁺and Er³⁺co-doped BaTiO₃ ceramics.As this method is based on the fluorescence peak wavelength dependence on the crystal environment,it may potentially be used to characterize the phase transitions in other ferroelectric materials.Li⁺and Er³⁺co-doped Ba CaTiO₃ ceramics with in various proportions of Ba²⁺and Ca²⁺were synthesized by high temperature solid state reaction.The effects of the introduction ratio of Ca²⁺on the ferroelectric,dielectric and piezoelectric properties of Ba CaTiO₃ based ceramics were studied.It is found that the phase transition of bacatio3 based ceramics tends to be dispersed with the increase of Ca²⁺ratio.Through the up conversion fluorescence spectrum intensity of ⁴S_3/2 energy level of Er³⁺,the dispersed phase transition of Ba CaTiO₃ based ceramics was successfully detected,and the dispersion degree of phase transition can be characterized at the same time.The application of fluorescence method in detecting phase transition in ferroelectric materials is expanded.