Study Of ZnO Effects On Optical And Electrical Properties Of Ho³⁺ And Yb³⁺ Co-doped BNT-based Ceramics

As an indispensable part of the development of functional devices,piezoelectric ferroelectric materials have been successfully applied to different fields such as transducers,sensors and ferroelectric memories.Lead-free materials have become a development trend due to their green-friendly type.BNT-based ceramics has been widely studied as one of the most promising lead-free piezoelectric ferroelectrics,among which 0.94Bi_0.5Na_0.5TiO₃-0.06BaTiO₃?BNT-6BT?is located near the morphotropic phase boundary of the system,and its electrical performance is optimized.The excellent piezoelectric and ferroelectric properties of BNT-6BT ceramics are used as the matrix material to study the optical properties of rare earth ions.By adding ZnO,the electrical properties and optical functions are maximized.Therefore,rare earth doped BNT-6BT ceramics integrate the electrical properties of ferroelectrics and the luminescence properties of rare earth ions,which can realize the electro-mechano-optical conversions.In this paper,ZnO and Ho³⁺,Yb³⁺co-doped BNT-6BT ceramics were prepared by traditional sintering process.The optimum sintering temperature was determined by XRD and SEM techniques.The crystal structure and surface morphology of the samples were characterized.The pure BNT-6BT ceramic is a perovskite phase structure.ZnO will exist in the form of the second phase in the ceramic to form a 0-3composite structure.It can be seen from the SEM image that the addition of ZnO has a positive effect on the change of crystal grains,and promotes the secondary growth of crystal grains.The crystal grains are more compact.the porosity is significantly reduced,and the density of ceramic samples is increased.According to the P-E curve,the addition of ZnO produces oxygen vacancies,which causes a slight decrease in ferroelectric properties.It is determined by dielectric temperature spectroscopy that the addition of ZnO delays the depolarization temperature T_d of the BNT-6BT sample and verified by the temperature dependence of the remaining d33.As the research focus of this thesis,we conducted optical test of rare earth ions doped ceramic samples.The experimental results show the relationship between the upconversion and downconversion luminescence intensity as a function of ZnO content.It was found that the addition of ZnO increased the luminescence intensity.The enhancement range is up to 2 times.The dependence of the luminescence intensity on the pump power is used to give the upconversion luminescence mechanism of rare earth ions,which explains the ZnO enhanced luminescence.ZnO is used as the medium for energy transfer.980 nm radiation light to provide suitable energy for ZnO crystal lattice,then part of the absorbed energy is transferred to Ho³⁺by the phonon mediating process to enhance fluorescence.In-situ tuning luminescence as a challenging topic has been a hot topic of research.In this experiment,the influence of in-situ electrical polarization on luminescence intensity was explored,and the change rule was found to be luminous with the increase of electric field.The intensity first increased slowly and then increased sharply and finally tended to be flat,with a maximum increase of 18.3%.We interpret the phenomenon by the P-E characteristic curve of ferroelectrics.The change caused by the electric field comes from the enhancement of lattice asymmetry,which leads to the increase of the probability of electric dipole transition in the 4f configuration of rare earth ions and the enhancement of luminescence.The research results of this thesis experimentally realize the integration of opto-mechanical functions of rare earth doped ferroelectric materials.The positive influence of ZnO on the electrical properties of ferroelectric materials and the luminescence intensity of rare earth ions has provided a new and unique direction for enhancing the multifunction of materials.