Rare-Earth Ion Er/Yb Co-Doping To Optimize The Phase Structure And Optoelectronic Properties Of KNN-Based Fluorescent Transparent Ferroelectric Ceramics

Transparent ferroelectric ceramics are multifunctional optoelectronic ceramics with good optical and electrical properties,which are widely used in the field of transparent electronic components such as sensors,storage,and capacitors.Among them,lead zirconate titanate（PZT）-based ceramics predominate.However,these ceramics have high lead content and can cause irreversible harm to the environment and humans in industrial production and everyday applications.(K_0.5Na_0.5)Nb O₃（KNN）ceramics possessed high Curie temperature,piezoelectric coefficient,electromechanical coupling coefficient,and good ferroelectric properties which are considered as ideal candidates for PZT-based ceramics.In this paper,KNN-based transparent ferroelectric ceramics were synthesized based on environmentally friendly KNN ceramic materials by introducing a second group component to modulate its structure and properties.In addition,the KNN-based transparent ceramics are doped with rare earth ions Er and Yb to obtain excellent up-conversion luminescence properties.The modulation of the structure and properties of KNN-based ceramics by Er/Yb co-doping has been investigated in detail,and the effect of the rare earth ion content on the luminescence properties has been highlighted.（1）（1-x）(K_0.5Na_0.5)Nb O₃-x Ba(Bi_0.5Ta_0.5)O₃（KNN-x BBT）transparent ferroelectric ceramics were synthesized by conventional solid-phase sintering methods.At x=0.025,the ceramic achieves a large transmittance of 68%at 1100 nm,a large dielectric breakdown electric field of 200 k V/cm,and excellent energy storage and dielectric properties with energy storage density,energy storage efficiency,and dielectric constant of W_rec=1.41J/cm³,η=42%,andε_r=1380,respectively.The dispersion index indicates that KNN-x BBT ceramics are relaxed ferroelectrics.（2）Based on the study of the introduction with BBT in KNN ceramics,the chemical composition of the second group component is adjusted to the requirements of chemical valence and ionic radius.（1-x）(K_0.5Na_0.5)Nb O₃-x(Sr_0.5Ba_0.5)(Bi_0.5Nb_0.5)O₃（KNN-x SBBN）transparent ferroelectric ceramics were prepared by the conventional solid-phase sintering method.At x=0.06,the ceramic obtains a maximum transmittance of up to 81.24%at 1100nm,but its electrical properties are reduced,with energy storage density,energy storage efficiency,and dielectric constant of W_rec=1.02 J/cm³,η=27.76%,andε_r=1206,respectively.The P-E hysteresis line gradually become more elongated,indicating a tendency for the KNN-x SBBN ceramics to shift further towards relaxation ferroelectrics.（3）On the basis of KNN-0.06SBBN ceramics with the best light transmission,the up-conversion luminescence is achieved by doping with rare earth Er ions.The conventional solid-phase sintering method was used to synthesize 0.94KNN-0.06SBBN:xwt%Er³⁺(KNN-SBBN:xwt%Er³⁺)fluorescent transparent ferroelectric ceramics,and it is found that the introduction of Er³⁺still yields an excellent transmittance of 80.14%at 1100nm and excellent luminescence properties.At x=0.4,for the red emission peak exhibits an emission intensity as much as four times higher than that at x=0.3.Furthermore,the addition of Er³⁺effectively improves and enhances the electrical properties of the KNN-based ceramics with energy storage density,energy storage efficiency and dielectric constant of W_rec=1.25 J/cm³,η=58.56%,andε_r=857,respectively,and still maintains a large dielectric breakdown electric field of 220 k V/cm.The dispersion index indicates that KNN-SBBN:xwt%Er³⁺ceramics are relaxed ferroelectrics.（4）The 0.94KNN-0.06SBBN:0.2wt%Er³⁺/ywt%Yb³⁺(KNN-SBBN:Er³⁺/ywt%Yb³⁺)fluorescent transparent ferroelectric ceramics were prepared by conventional solid-phase sintering method,and it is found that the addition of Yb³⁺greatly improves and enhances the electrical properties of the KNN-based ceramics with energy storage density,energy storage efficiency and dielectric constant of W_rec=1.33 J/cm³,η=76.18%,andε_r=1082,respectively.At the same time,higher dielectric breakdown fields and transmittance are still obtained,250 k V/cm and 71.7%,respectively.In addition,the Er/Yb co-doping gives the KNN-SBBN:Er³⁺/ywt%Yb³⁺ceramics excellent luminescence,with green and red light intensity enhanced by a factor of about 27 and 77 compared to the KNN-SBBN:0.2wt%Er³⁺ceramics.The progressively broader dielectric peaks exhibit frequency dispersion behavior and the T_m peak moves towards lower temperatures,indicating a tendency for the ceramics to transition into relaxed ferroelectrics.