Study On Energy Transfer And Luminescence Properties Of Ions Doped In Polycrystalline Hexagonal Alkaline Earth Aluminate

In recent years,white light emitting diode(WLED)has become an important light source due to its high luminous efficiency,long life,high brightness,low prepa-ration cost and other advantages.As the activator of WLED phosphor,rare earth ions play an important role.They have a variety of colored emitted based on the f?f and f?d transitions.Tb³⁺ion is a common green light activator,and the⁵D₄?⁷F₅transition at 544 nm leads to the main green light emission.However,due to the existence of the forbidden transition of the 4f?4f,the absorption efficiency will be reduced and lead to the luminescence intensity will be decreased.To enhance the absorption of Tb³⁺ions,it is considered that the co-doped ion as sensitizers to increase its absorption efficiency to improve its luminescence intensity.In this thesis,two kinds of polycrystalline hexagonal alkaline earth aluminates doped with rare earth ions were prepared by high temperature solid state reaction,Ba Zn_1.06Al_9.94O₁₇(BZAO)and Sr Mg_1.06Al_9.94O₁₇(SMAO)were used as the matrix,doped Tb³⁺?Eu³⁺or co-doped Tb³⁺,Bi³⁺and Tb³⁺,Ce³⁺.The energy transfer of these ions,luminescence properties and structures of the prepared samples were studied by measuring X-ray diffraction pattern,fluorescence spectrum,temperature variation spectrum and fluorescence lifetime.The conclusions are as follows:(1)BZAO:Tb³⁺phosphor has excitation band at 228 nm,which belong to the⁵D₄?⁷F₅transition of Tb³⁺,and it emitted green light due to the transition of⁵D₄?⁷F₅.However,when Bi³⁺ions co-doped with Tb³⁺,the excitation peak red shifted to 265 nm due to the transition of Bi³⁺ions,and the energy transfer of Bi³⁺ions to Tb³⁺caused the emission intensity at 544 nm of the sample was increased by about 10 times.In addition,the chromaticity coordinates of BZAO:Tb³⁺phosphors were 2.2396 and 0.5063.And the variable temperature spectra of the samples were analyzed in the range of 300 to 500 K,and the logarithm of the emission intensity at 544 nm showed a good linear relationship with the temperature.(2)Ce³⁺ions were also co-doped in BZAO:Tb³⁺.Compared with BZAO:Tb³⁺,the X-ray diffraction patterns of samples co-doped with Ce³⁺have no obvious changes.In the excitation spectrum,the same as the co-doped Bi³⁺ions,the excitation peaks show obvious red shift.A wide excitation band appears in the range of 240-320 nm,which is caused by the 4f?5d transition of Ce³⁺ions.However,only Tb³⁺ions characteristic emission appeared in the emission spectrum.The emission intensity is increased by about 15 times due to the energy transfer from Ce³⁺to Tb³⁺.(3)After Tb³⁺and Ce³⁺co-doped with SMAO host,the excitation band of4f?5d transition of Ce³⁺appeared at 269 nm in the excitation spectrum.The emission intensity of the sample is increased by about 27 times after co-doped Ce³⁺ions,which indicated that Ce³⁺ions as sensitizers transferred energy to Tb³⁺ions.(4)Under the excitation of 331 nm,the emission band of 5d?4f transition of Eu²⁺ions centered at 444 nm appears in the emission spectrum of BZAO doped Eu ions,and the emission peak of⁵D₀?⁷F₂transition of Eu³⁺ions is also observed at 612 nm.The abnormal reduction of Eu²⁺ions in the air and the coexistence of Eu²⁺and Eu³⁺were explained.