| With the continuous growth of China's economy and increasing energy consumption,energy shortages and environmental pollution have become two major problems that constrain the further development of China's economy.The development of new clean energy and environmental pollution control has become the focus and hotspot of scientific research.Among many new clean energy sources,solar energy is a clean renewable energy source with potential applications.Photocatalytic technology,which can effectively use solar energy and convert solar energy into chemical energy,is one of the most potential solutions to future energy and environmental problems However,the current photocatalytic efficiency is still low,which has become the most important problem that restricts its development and practical application.The photocatalytic efficiency is mainly determined by two factors:the light absorption range of the photocatalytic material and the carrier separation efficiency.Therefore,further expanding the light absorption range of the photocatalytic material and improving the carrier separation efficiency are the key to further improve the photocatalytic efficiency and promote the development of photocatalytic technology and its applicationAt present,photocatalytic materials generally only absorb ultraviolet and visible light,and the utilization of infrared light,which accounts for 50%of the solar spectrum energy,is low.The up-conversion material can convert in frared light into higher-energy ultraviolet light and visible light,which can be absorbed by the semiconductor,and is one of the important means to expand photocatalysis using in frared light.However,the infrared photocatalytic efficiency of the upconverted photocatalytic materials is generally lower,which greatly limits the development of infrared photocatalytic materials.Therefore,it is of great significance to further improve the infrared photocatalytic activity of the upconverted photocatalytic material and design and prepare a novel high-efficiency upconversion photocatalytic materialIn this thesis,we start from the up-conversion luminescent materials,further improve the up-conversion luminescence efficiency by studying the up-conversion luminescence process and mechanism,and combine the design theory of semiconductor photocatalytic materials with the microstructure control method to explore and prepare several high-efficiency Bi-based upconversion photocatalytic functional composites simultaneously achieve up-conversion and photocatalytic functional recombination in the same material,which not only further enhances its infrared photocatalytic activity,but also further expands upconversion photocatalysis in biomarkers and photodynamics.The application of the aspect provides a new preparation method and material system.In the first chapter,this paper introduces and analyzes the basic principles and research progress of rare earth upconversion luminescence,the basic principles and research objectives of semiconductors,and the design and research status of upconversion photocatalysis.On the basis of early research,we put forward our own ideas.The work of this thesis is divided into the following five parts:In the second chapter,the wide-bandgap semiconductor LaNbO4 was used as the matrix doping sensitizer Yb3+ ion and activator Er3+/Ho3+/Tm3+ ions,and the up-conversion luminescence properties of different activator ions were explored in detail.Under the excitation laser at 980 nm,the main luminescence peaks of LaNbO4:Yb3+and Er3+ are at 525,550,660 nm,respectively,corresponding to two green lights and one red light.The main luminescence peaks of LaNbO4:Yb3+ and Ho3+ are respectively at 550,650,750 nm.The positions correspond to a green light and two red lights respectively;the main luminescence peaks of LaNbO4:Yb3+ and Tm3+ are respectively at positions of 475 and 650 nm,corresponding to a blue light and a red light,respectively.This lays the foundation for the next step of selecting suitable narrow-bandgap semiconductors and doped rare earth elements.In the third chapter,NaYF4:Yb3+,Tm3+@NaYF4:Yb3+,Nd3+@TiO2(ie Tm@Nd@TiO2)core@shell nanoparticles were prepared by solvothermal method and their infrared photocatalytic activity was studied in detail.Due to the presence of the core@shell nanostructure,the quenching of the upconverting luminescence is reduced,so that the upconversion luminescence intensity is increased by 35 times under 980 nm irradiation.The absorption range of visible and infrared light of the material is greatly extended,and the up-conversion luminescence is further improved.The improvement of up-conversion luminescence based on the core-shell structure and Nd3+ ions further enhances and enhances the UV-Vis-NIR photocatalytic activity.This result can promote the further development of near-infrared light-responsive photocatalysts and can promote practical applications in other fields.In the fourth chapter,the doping of the sensitizer Yb3+ ion and the activator Tm3+ion by using the narrow band gap oxide BiVO4 as a substrate produces strong single red light emission and infrared photocatalytic effects under near-infrared light.This design combines the photocatalytic performance of the BiVO4 semiconductor with the upconversion luminescence position of the activator Tm3+ ion,since the absorption range of the semiconductor BiVO4 just contains the strong blue light emission of the Tm3+ ion.In addition,the Bi3+(1.08 A)ionic radius is similar to the ionic radii of Tm3+(0.869 A)and Yb3+(0.858 A),making it easy to dope a lot of rare earth ions.In the sample BiVO4:Yb3+,Tm3+,although BiVO4 itself cannot respond to infrared light,the blue and other higher energy emission emitted by the activator Tm3+ in BiVO4:Yb3+,Tm3+ is absorbed by the matrix BiVO4,and the high-energy emitted light absorbed by the matrix Electron-hole pairs are generated in the matrix,so that BiVO4:Yb3+.Tm3+has a photocatalytic action under near-infrared light.Studies have shown that the use of semiconductor oxides as a matrix of sensitizers and activator ions enables single-wavelength upconversion luminescence and photocatalytic activity in near-infrared illumination.This conclusion has led to the development of novel single-red upconversion luminescence and infrared.Photocatalytic materials have important guiding significanceIn the fifth chapter,the narrow bandgap oxide semiconductor Bi20TiO32 is used as a matrix of Yb3+ aId Er3+ ions to produce strong single red light emission and high photocatalytic activity under near-infrared light irradiation.Because the main upconversion luminescence peak of Er3+ ion is located at 540 and 660 nm,and the upconversion strong green luminescence of activator Er3+ at 540 nm matches the narrow band gap of Bi20TiO32,it can be effectively absorbed by Bi20TiO32 and produce strong single red emission.The absorbed green upconversion luminescence enables the Bi20TiO32 matrix to generate electron-hole pairs,which exhibits good photocatalytic activity under near-infrared light.At the same time,the doping of Yb3+ and Er3+ ions can double the specific surface area and provide more active sites to promote the improvement of photocatalytic efficiency.Studies have shown that narrow bandgap semiconductor oxides doped with Yb3+ and Er3+ can be used as effective UV-Vis-NIR response photocatalysts and achieve strong single red emission in near-infrared light.In the sixth chapter,the high temperature ? phase of Bi2O3 can be stabilized by doping rare earth elements,and the Yb3+,Er3+ or Tm3+ ions are doped into the Bi2O3 lattice.The doping concentration can be increased to induce Bi2O3 from a phase to ?phase.Continuous phase transition to the ? phase.Based on this,three pure phases of?-,?-and ?-Bi2O3 and two heterophase junctions of ?-/?-Bi2O3 and ?-/?-Bi2O3 were synthesized.At the same time,the incorporated Yb3+,Er3+ and Tm3+ can achieve up-conversion luminescence.Under the excitation of infrared light,the sensitizer Yb3+can absorb near-infrared light and transfer energy to the activator Er3+ or Tm3+ to generate ultraviolet-visible upconversion luminescence,which is absorbed by the narrow band gap Bi2O3.Based on this,the prepared Yb3+,Er3+ and Tm3+ co-doped ?/?-Bi2O3 and ?-/?-Bi2O3 are out of phase,and at the same time,strong single red light emission,efficient carrier separation and passage are realized.Up-conversion extends the absorption spectrum from light to infrared light,ultimately achieving efficient UV-Vis-NIR photocatalytic activity.In the seventh chapter,we have made a comprehensive summary of the research content of this thesis,and proposed and analyzed the shortcomings in the current work,and prospected the future research work.In summary,the exploration of high-efficiency upconversion photocatalytic materials with infrared light response is of great significance to further improve solar energy utilization efficiency and promote the development and application of photocatalysis technology.In this paper,we further improve the upconversion photocatalytic efficiency by studying the upconversion luminescence mechanism and matrix materials,and explore several Bi-based photocatalytic materials that can be used as up-conversion luminescence mechanisms to further improve upconversion photocatalysis.At the same time of activity,the functional combination of up-conversion and photocatalysis is realized,which is of great significance for promoting the development of up-converting photocatalytic materials,and has important value in the practical application of up-conversion biomarkers and photodynamic therapy. |
PDF Full Text Request