Photochromism、Temperature Sensing And Photocatalytic Properties Of Er/Yb Co-doped Bismuth Layered Materials

With the progress of technology and the advent of the information age,all kinds of optical components are gradually developing towards miniaturization and multifunction,which puts forward higher requirements for the performance of materials.Bismuth layered materials often have efficient luminescence properties by introducing rare earth ions.At the same time,these materials often have obvious photochromic reaction under the irradiation of specific wavelength light.The combination of these two properties makes bismuth layered materials widely studied and applied in the field of multi-dimensional optical anti-counterfeiting and optical information storage.Moreover,due to the narrow band gap,bismuth layered materials are very excellent semiconductor catalyst.With the increasingly serious pollution of industrial wastewater,the research on photocatalytic degradation of organic pollutants in water using this material has also entered a new active period.However,most of the current reports on bismuth layered materials only focus its individual properties,but do not systematically study its various optical properties.Based on this,we prepared a series of bismuth layered materials by rare earth doping,and explored the impact of structural changes on its optical properties,and systematically analysed the relationship between upconversion luminescence,photochromism and photocatalysis.Finally,it was found that the rare earth doped bismuth layered materials have potential applications in optical information storage、contactless temperature measurement、organic pollutant degradation and other fields.Er³⁺/Yb³⁺co-doped bismuth titanate(Bi_3.96Ti₃O₁₂),sodium bismuth titanate(Na_0.5Bi_4.46Ti₄O₁₅)and their intergrowth structure samples(Na_0.5Bi_8.46Ti₇O₂₇)were prepared by traditional solid-state sintering method.The effects of intergrowth structure on the upconversion luminescence,photochromism,and temperature sensing properties of the samples were investigated respectively.The luminescence modulation ratio（ΔR_t）for the sample(Na_0.5Bi_4.46Ti₄O₁₅)with intergrowth structure reached 77.25%,and the temperature sensing sensitivity S_a and S_r were 0.00518K^-1 and 1.23%K^-1 respectively.Compared with other two samples(Bi_3.96Ti₃O₁₂,Na_0.5Bi_4.46Ti₄O₁₅),the sample with intergrowth structure has better optical information storage and temperature sensing characteristics,which provides a new idea and direction for the application of bismuth layered ferroelectric materials with intergrowth structure in the optical field.Pure Na_0.5Bi_4.5Ti₄O₁₅ and Na_0.5Bi_4.49-xTi₄O₁₅:0.01Er/x Yb（0.005<x<00.2）ceramic samples and powder were prepared and studied from three aspects:photochromic effect,temperature sensing and photocatalysis.The related mechanisms of photochromism-modulated upconversion luminescence and photocatalysis were explained.Firstly,after405nm laser irradiation,the sample has a photochromic reaction.Due to the energy transfer between the luminous center and the color center,the upconversion luminescence shows a strongly dependence on the photochromic reaction,and its maximum luminescence modulation ratio reaches 78.02%（x=0.05）at 520nm.Secondly,the temperature sensing characteristics of the samples were tested in the range of 298K-688K.The maximum relative sensitivity S_r reached 1.41%K^-1（x=0.01）,which was at a high level among the different matrix materials co-doped with erbium and ytterbium reported in recent years.Finally,in the photocatalytic experiment,the catalytic performance of the sample irradiated by simulated sunlight was significantly improved,and the maximum degradation rate D value of pure Na_0.5Bi_4.5Ti₄O₁₅ reached 75.06%.This is coming from the internal electric field generated by photochromic reaction,which inhibits the recombination of photogenerated carriers,thus improving the efficiency of photocatalytic reaction.