Adjustment Of Crystal Types And Luminescence Of Rare-earth Ions Doped Polymorph Hosts

Rare earth luminescent materials composed of luminescent matrix and rare earth luminescent center are widely used in lighting,display fields.As the host of luminescent center,the local crystal field environment of different crystal type host will have a great impact on the energy level transition of doped rare earth ions.Therefore,the host with a same stoichemietric chemical composition but with different crystal tructure will exhibit some distinct luminescent properties by some means to control the crystal types of the luminescent host.In this thesis,several hosts of Al₂O₃,Y2Si2O7(YPS),and Na₃V₂(PO₄)₃ with polymophism features were investigated through doping Eu²⁺/Ce³⁺into the hosts by fine-tuning the crystal types.The luminescent properties and differences of rare earth ions in polymophism hosts were investigated.The main achievements are as follows:1.The Al₂O₃ with the aboundant polymorphism feature was selected as the luminescent host.By controlling the reaction temperature,Eu²⁺ion-doped?-,?-,?-and?-different crystal phosphors were prepared respectively.The experimental results show that Eu²⁺ions have different emission peak positions for?-,?-,?-Al₂O₃ at 410nm,450 nm and 480 nm,respectively.But for Eu²⁺-doped?-Al₂O₃ phosphors,with the increase of doping concentration,the emission peak position is red-shifted from 410nm to 500 nm,more like due to high concentration effect of doped Eu²⁺ions in?-Al₂O₃.Segregation of boundaries for Eu²⁺ions resulted from the occupation at different lattice sites in the host.By carefully looking insight into the details,the correlation between alumina crystal structure and luminescence properties was established.2.The YPS homogeneous polycrystal is selected as the luminescent host.Ce³⁺-doped?-,?-and?-YPS phosphor materials were prepared through the solid solution of La³⁺ions and the control of the reaction temperature.It is found that the profiles of the excitation spectra corresponding to different crystal forms are quite different.For?-YPS,there are two excitation peaks in the excitation spectrum,while for the other two crystal forms,there are three peaks in the excitation spectrum.For the emission spectra,there are four possible sites for Y³⁺in the?-YPS crystal structure.The spectra for coordination of Y(1),Y(2)and Y(4)are similar to exhibit in a double-triangular prism,and the fourth Y³⁺ion is located in a twisted octahedron with six-fold coordination.However,there is only one possible site for?-YPS and?-YPS,the emission spectrum of?-YPS sample exhibits peak position broadening compared to other crystal types.3.Na₃V₂(PO₄)₃ polycrystals with different Eu²⁺ion concentrations were prepared?-Na₃V₂(PO₄)₃phosphor material,the optimized doping concentration of Eu²⁺was obtianed,and the negative thermal quenching phenomenon was investigated.Meawhile,the replacement of Zr⁴⁺for V³⁺resulted in an increase of the luminous intensity of the phosphor and the emission peak is red shifted slightly by doping Al³⁺.