Research On The Calcium Aluminate Long Afterglow Phosphorescent Material Fabricated From Combustion Synthesis

CaAl₂O₄-based long afterglow phosphors were studied in this thesis.The luminescent brightness and time of the phosphors can be improved greatly by adjusting the concentrations of the activators in the proper range and the compositions of the host. Other factors that affected the luminescent properties of the long afterglow phosphors were also studied. The luminescent mechanism of the long afterglow phosphors was elementarily discussed.The experiments revealed that the luminescent brightness of the CaAl₂O₄:Eu²⁺,Nd³⁺ long afterglow phosphors greatly depended on the concentration of Eu²⁺ and Nd³⁺. When the content of Eu²⁺ was 2%, the luminescent properties was the best. When the raw materials doped with assistant activator of Nd³⁺, the luminescent brightness of phophors enhanced, and luminescent time also prolonged. When Nd³⁺/Eu²⁺ was 1:1 , the luminescent brightness was the best.The effect of flux, temperature and CH4N2O dosis on CaAl₂O₄:Eu²⁺,Nd³⁺ were discussed, and then the optimum combustion synthesis conditions were determined. The study found that when the content of H3PO3 was 15%, the temperature was 600℃,and the ratio of CH4N2O/NO3- was 2:1, the luminescent properties was the best. Through the XRD patterns, SEM map, fluorescence spectra of the samples, crystal structure, surface pattern and excitation﹑emission spectra were studied. The minute changes of matrix composition had some degree effects on the afterglow characteristic, through the experiments, the sample identified as Ca0.93Al₂O₄:Eu0.02²⁺,Nd0.02³⁺ had the best afterglow characteristic. With the change of"x", the crystal structure of CaxAl₂O₄:Eu0.02²⁺,Nd0.02³⁺ changed.With the reduction of"x", the impurities peak increased obviously, and the diffraction peak intensity of CaAl₂O₄ gradually weakened. There is no effect on fluorescence spectra.Phosphor luminescence properties can be improved by Sr. After entering the lattice, Sr²⁺ replaced the position of Ca²⁺, but doesn't form new phases. In addition, lattice parameter was increased because of the introduction of Sr²⁺ . The blue shift phenomenon were observed when Sr²⁺ increased.Synthetic reaction revealed that the luminescent properties of CaAl₂O₄: Eu²⁺,Nd³⁺ cannot be improved by Sm³⁺, but can be improved with codoped of Pr³⁺,Dy³⁺,Gd³⁺ and Nd³⁺. CaAl₂O₄:Eu²⁺,Nd³⁺,RE³⁺ still belonged to the monoclinic system, and there was no other phase occurred. The lattice parameter enlarged when the radius of RE³⁺ increased. The peaks of excitation and emission spectra were 334nm and 442nm, which corresponded to the transition between 4f7 and 4f65d1 of Eu²⁺.Activation theory of Eu²⁺ ion was studied: 5d orbit which exposed in the outer layer of Eu²⁺ was influenced strongly by crystalline field environment. So among long afterglow materials, different crystal structure leaded the different energy band splitting extent, thus emission peak changed. The luminescent mechanism of aluminate long afterglow materials were raised, which can explain excellently the contribution of different rare earth ions.