Research On The Photochromic Properties And Luminescence Modulation Of Er Ions Doped (Na_0.5Bi_0.5) TiO₃ Based Ceramics

Inorganic photochromic materials,which have superior mechanical strength,and thermal stability and chemical stability,are potential candidates in optical information storage,optical switches and optical anti-fake labels.In this thesis,Er doped Na_0.5Bi_0.5TiO₃（NBT）based ceramics are selected as the main research objects.A series of NBT based and its composites were synthesized by the solid-state reaction sintering method.The photochromic properties of NBT based ceramics were optimized by improving photochromic efficiency,sintering temperature,reaction time and irradiation wavelength.The mechanism of the enhanced photochromism and fluorescence modulation relationship of polarized ceramics were further explored.The Er-doped NBT inorganic photochromic ceramic materials and Er-doped（1-x）NBT-xKNN binary inorganic photochromic materials have been prepared.Furthermore,the ferroelectric,photochromism and luminescence modulation of the resultant ceramics were systematically investigated through analyzing their macroscopic performance and microstructure.1.A novel inorganic photochromic（PC）material was developed through introducing the Er into NBT ceramics.Its corresponding factors affecting photochromism were studied in detail,and the tunable luminescence in photochromic ceramic was studied by an electric field poling.Based on the achieved result,we found that the degree of photochromism is dependent on the sintering temperature,sintering time and irradiation wavelength of NBT:0.002Er ceramics.The coloring and decolorization of the NBT:0.002Er ceramics were examined after 10 cycles.It is found that there was no obvious decay for all the studied samples,indicating an excellent anti-fatigue property.In addition,it has been found that the polarized ceramics have excellent fluorescence modulation properties after irradiation.Ultimately,the enhanced luminescence modulation mechanism of the polarized NBT:0.002Er ceramics was further clarified by the structural transition,dielectric behavior and domain structure changes before and after polarization of the material.2.A binary solid solution of（1-x）NBT-xKNN:0.002Er（x=0.02,0.04,0.06,0.08,0.10 and0.12）ceramics have been developed.The evolution of ferroelectric,dielectric behavior and photochromic of ceramics with increasing KNN content was investigated.With the increasing KNN content,the degree of ergodicity is enhanced.For compositions of（1-x）NBT-xKNN:0.002Er ceramics with x=0.02,0.04 and 0.06 that exhibit strong nonergodicity,the PC reaction and luminescence contrast can be greatly enhanced via an electric field poling because of the forming of a long-ranged order ferroelectric state in them.Meanwhile,the compositions of（1-x）NBT-xKNN:0.002Er ceramics with x=0.08,0.10 and 0.12 have an opposite effect after electric poling.Such an opposite poling effect on the PC reaction and luminescence contrast is strongly related to the ergodicity of the ceramics.It was explained from the microdomain structure.The experimental results further reveal that polarization enhancement is closely related to unique the domain structure of NBT-based ceramics.