Synthesis And Photo-thermal Property Of Reduced Graphene Oxide/NaGdF₄:Yb,Er Nanocomposites

Nanocomposites composed of graphene oxide（GO）and inorganic functional nanocrystals have attracted considerable attention not only because of fundamental scientific interest but also for immense potential of overcoming the problems in the fields of life science,energy,and the environment.The hexagonal phase NaGdF₄ upconversion nanoparticles（UPNS）are considered to have great potential application in photothermal therapy and bimodal imaging,i.e.optical bioimaging and magnetic resonance imaging.However,a few works reported are focusing on the nanocomposites composed of GO and Yb,Er codoped NaGdF₄.Recently,several efforts have been made in the fabrication methods of GO based UP nanocomposites.Those preparation methods are involved a multistep surface modification of GO and UPNS.Toxic,expensive raw materials are required in those methods.The luminescence from UPNS is completely quenched by GO.It is urgent to develop a facile route for the synthesis of GO based nanocomposites with visible UC luminescence and explore the relationship between the structures and properties of nanocomposite.Fristly,in this thesis,NaGdF₄:Yb,Er/reduced GO（NaGdF₄/rGO）composites are synthesized by a two-step method.In this method,graphene oxide/GdF3:Yb,Er（GdF3/GO）composites are obtained by a simple hydrothermal route.And then,as-prepared GdF3/GO is annealed at different temperature in N2 atmosphere.The structure change from GdF3/GO to NaGdF₄:Yb,Er/reduced GO（NaGdF₄/rGO）composites is confirmed.The relationship between structure change and the improved UC luminescence of composites is also given in detail based on the analysis of photo induced electron transfer from the UPNS to the energy receptor in GO substrate.Secondly,a facile microwave reaction is used to prepare NaGdF₄/rGO composites.Microwave time influences the structure change from cubic NaGdF₄ to hexagonal NaGdF₄ and the luminescence intensity of composite.However,the fewer adding quantity of GO is,the better luminescence intensity of composite is.Finally,we design a near-infrared photothermal tester.It is used to investigate the photothermal efficiency of NaGdF₄/rGO water solution.The photothermal efficiency of composites obtained by two-step method is 55%,which is lower than composites obtained by microwave route,70.1%.