Long-Persistent And Near-Infrared Phosphors Based On Spinels: Controlled Synthesis And Luminescence Mechanism

In this dissertation,long-persistent and near-infared phorsphors of ZnGa2O4:Cr3+,Yb3+/Er3+,Zn3Ga2Ge2O10:Cr3+ and Zn3Ga2Ge2O10:Cr3+,Li+based on spinels have been obtained by hydrothermal and sol-gel processing with emphasis on the tunable composition and morphology.The luminescent properties and afterglow emission mechanism were defined,and the spinel phosphors were successfully applied in cell imaging and bioimaging.Detailed characterizations of the samples were achieved by combined techniques of XRD,FE-SEM,HR-TEM,STEM,SAED and PLE/PL long-persistent decay curve analysis,and the main achievements are listed as follows.Monodispersed spheres of ZnGa2O4:xCr3+,Yb3+/Er3+(x=0.001-0.010)and Zn3Ga2Ge2O10:Cr3+ with a diameter of?200 nm have been hydrothermally synthesized followed by calcinations,which are polycrystalline and maintain the original morphology after calcined at 800?.The partical size is singnificantly affected by metal ion concentration,hydrothermal temperature,hydrothermal time and pH value,and it increased with a higher concentration of citrate anions(Cit3+).The optimized processing condition of was defined as follows:synthesizing at 180? for 18 h with pH=5 and Cit3+/M molar ratio of 1(M=total cations).Under the ultraviolet radiation excitation,the spinel spheres exhibit classical near-infrared emission centered at 695 nm,whose fluorescence intensity is still extremely strong after stoping UV irradiation on account of the existence of the antisite defects.Meanwhile,under the 980 nm infrared excitation,Yb3+/Er3+-doped sample exhibits red emission centered at 661 nm(visible light),and it exhibits near-infared emission centered at 695 nm after stoping UV irradiation for half an hour,which has been successfully applied in imaging of cancer cells.The excited state energy level could be selectively influenced by the Zn element content of the host.The energy level of 4T2 is not distinctly impacted by the Zn content,while higher Zn content induced the come up of conduction band bottom and the move down of energy level 4T1.The single-crystalline particles of Zn3Ga2Ge2O10:xCr3+,yLi+with a diameter of 100-200 nm have been obtained by calcining the precursors at 1000?.Particle morphology,crystal structure,lattice structure are not obviously influenced by Cr3+ and Li+ doping,which is homogeneous solid solution.Under the 273 nm excitation,the phosphor exhibits typical near-infrared emission centered at 697 nm,and the enhanced fluorescence intensity was observed with increasing the calcination temperature.The fluorescence intensity of phosphors is not visibly influenced whether Li+-doped or not,while the afterglow decay has been slowed down and then the afterglow time was extended,mainly due to that the electron located at the deeper traps would be released slowly after thermal disturbance owing to the increasing of the charge compensation defects content along with more Li+-doping.Among that,the sample with the longest afterglow decay time has been obtained as the y value of 0.01.