Study On Structure Modification And Optical-electrical Properties Of Rare Earth Doped KNN Based Transparent Ferroelectric Ceramics

With the development of science and technology,more and more multifunctional devices are needed,and the research and exploration of multifunctional materials are more intense.Potassium sodium niobate?KNN?based lead-free ferroelectric ceramics not only have good piezoelectric,ferroelectric and other electrical properties,but also have optical transmittance by forming solid solution with tetragonal phase ABO₃ component.KNN transparent ceramics will play an important role for new lead-free ferroelectric materials in the future.In this paper,the KNN-Sr(Yb_0.5Nb_0.5)O₃ ferroelectric ceramics with light transmittance are obtained,and rare earth elements Ho and Er doped,ceramics have up-conversion luminescence property.Finally multifunctional ceramics with ferroelectric,transparent and luminous properties are obtained.In addition,0.94K_0.5Na_0.5Nb O₃-0.06Sr(Zn_1/3Nb_2/3)O₃ ceramics with high transmittance and energy storage density doped with Er obtain up-conversion luminescence characteristic.The main contents and conclusions are as follows:?1?The structure,light transmittance,electricity and energy storage properties of?1-x?K_0.5Na_0.5Nb O₃-x Sr(Yb_0.5Nb_0.5)O₃??1-x?KNN-x SYb N?ceramic were studied.XRD and Raman spectra show that the ceramics are pseudo-cubic structure.When x=0.175,the near-infrared transmittance of the ceramic is 20.9%,and the optical band gap Eg is 2.86 e V.After introducing Sr(Yb_0.5Nb_0.5)O₃,the grains of the ceramics are small and compact cubes.Heavy doping?x?0.20?will reduce the dense strcture and melt the surface grains.The ceramics are shown as relaxor ferroelectrics with good insulation.When x=0.175,the comprehensive energy storage performance is the best.At this time,the energy storage density Wrec and energy storage efficiency?are 0.21 J/cm³ and 78.2%,respectively.?2?The effects of rare earth Ho on the structure,luminescent and electrical properties of 0.825KNN-0.175SYb N ceramics were studied.After introducing rare earth Ho,XRD shows that the phase of ceramics changed from pseudo-cubic phase to orthorhombic-tetragonal phase.At this time,the light transmittance decreases,and large grains grow on the surface and its density also decreases.When x=0.20,the maximum Wrec reaches 0.26J/cm³,and the?reaches 87.1%.Under the excitation of 980 nm laser,the ceramics have up-conversion luminescence characteristic.The emission wavelengths are 550 nm and 670nm,and the ceramics have the best up-conversion luminescence performance when the Ho content is x=0.1.With the increase of Ho content,the concentration dependent quenching resulted in the decrease of the up-conversion luminescent intensity due to the cross relaxation of excessive Ho in the ceramics.When x=0.1,the ceramic poled in 40 k V/cm for half an hour increase the oxygen vacancies in the ceramic,make the crystal cell shrink,reduce the symmetry of crystal structure,increase the possibility of the radiation transition of rare earth Ho³⁺ion level.At the same time,polarization reduces the Eg value of the ceramic,and enhance the luminous intensity of the ceramic.?3?The effects of Er on the structure,luminescent and electrical properties of0.825KNN-0.175SYb N ceramics were studied.XRD shows that when Er doping content is low,the ceramics are pseudo-cubic phase structure.When the doping content is higher than1.0%,the ceramics turn to orthorhombic-tetragonal phase,and many large grains grow on the surface of ceramics.When the Er doping content x=0.25,the Wrec reaches the maximum value of 0.31 J/cm³,and its?reaches the maximum value of 94.6%.Meanwhile,the maximum strain is 0.031%.The dielectric temperature spectrum shows that the Curie peak is not influenced by the rare earth Er,and the maximum dielectric constant?_?can be effectively increased by appropriate rare earth Er.When x=1.00,the maximum?_?reaches1871.The rare earth Er improves the up-conversion luminescence characteristics of the ceramics.The wavelength of emission light is mainly around 550 nm and 650 nm.With the increase of Er doping content,the luminescence intensity first increases,and reaches the maximum at x=0.75.After further excessive doping rare earth Er,the energy levels of Er³⁺ions in the ceramics are cross relaxation,which makes the luminescent properties decrease.?4?The effects of Er doping on the structure,energy storage and luminescent properties of 0.94K_0.5Na_0.5Nb O₃-0.06Sr(Zn_1/3Nb_2/3)O₃ ferroelectric ceramics with high transmittance and energy storage properties were studied.The XRD shows that the ceramics are still pseudo-cubic phase structure,and the rare earth Er does not change the phase structure.Large grains grow on the surface,and its transmission of light is significantly reduced.The ceramics have good?,the?is as high as 80.3%when x=1.0,and the largest Wrec value is 0.36 J/cm³ when x=2.0.And the ceramics also have strain,the strain value is 0.033%when x=2.0.The dielectric spectra shows that the ceramics are relaxor ferroelectrics,and the Curie temperature does not change after introducing Er.The rare earth Er improves up-conversion luminescence property.When the doping content is low?x=0.25?,the energy level transition is mainly broadband gap transition.At this time,the energy level transition mainly originate from ²H_11/2?⁴I_15/2 and ⁴S_3/2?⁴I_15/2.With the increase of the Er³⁺doping content,the luminescence intensity also increases.When x?0.50,the energy level transition is mainly ⁴F_9/2?⁴I_15/2,and the luminescence intensity reaches the maximum when x=1.00.With the increase of the Er content,the luminescent intensity is quenched in a concentration-dependent manner.