Influence Of Rare Earth Substitution On Structure,photoluminescese And Electrical Properties Of Tungsten Bronze Oxides

Recently,up-conversion luminescence（UCL）based on rare earch（RE）doped ferroelectric（FE）hosts has received much interest.In contrast to previous extensively investigated FE hosts,this thesis mainly focuses on the novel tungsten bronze（TB）materials.We show that RE ions substitution can significantly modulates the crystal structure and performance of TB materials.This thesis is organized as following:（1）A series of Ba₄La_0.95-xGdx Er_0.05TiNb₉O₃₀ samples have been synthesized.It is found that enhanced UCL emission,obvious relaxor-like FE state and paramagnetic features have been simultaneously realized in this system with the incorporation of Gd3+.（2）The crystal structure of Sr_xBa_5.91-x Er_0.06Ti₂Nb₈O₃₀ has been investigated simultaneously by Rietveld structural refinement and UCL spectra.It is believed that UCL spectra can be explored as a structure probe for TB system.（3）A new series of plumbum-free Ba_3.75La_0.833-x Er_xNb₁₀O₃₀ oxides have been prepared.The crystal structure is determined as single phase unfilled tetragonal TB structure.It is indicated that the phase transitions and ferroelectric states are sensitive to x.in addition,the maximum temperature sensing sensitivity is found to be 0.0025K-1.（4）A series of K₂Bi_0.98-x Er_0.02YbxNb₅O₁₅（KBN-x）up-conversion nanoparticles（UCNPs）with different particle sizes have been prepared.It is found that synthesis temperature acts an important factor to determine the particle size.Furthermore,we show that particle size has an important influence on the sensitivity.（5）New unfilled TTB oxides Ba5-5x Sm5xTi5xNb10-5xO30 have been prepared.Dielectric and ferroelectric results indicate that phase transitions and ferroelectric states are sensitive to x.It is believed that c/a is a more appropricate parameter to illustrate the variation of FE properties for unfilled TB system.