The Synthesis And Luminescent Properties Of Three Rare-earth Doped Oxysalt Materials Based On 4f-5d Transition

After decades of study concerning luminescent materials,there are lots of reseaches and corresponding applications of rare-earth element doped oxysalt luminescent materials.For example,the Y3Al5O12(YAG):Nd crystal in laser device,YAG:Ce3+ phosphor used in white LED,LiAlsOs:Cr3+ used in fluorescent temperature sensing field,and the persistent luminescent material of SrAl2O4:Eu2+,Dy3+ used as safety sign.In view of some relevent problems in the applications of rare-earth element doped oxysalt luminescent material,we conduct the current studies in this dissertation.As for the excitation or emission investigated in our researches,the 4f(?)5d transitions of rare earth ions are involved as major processes.The first chapter is the introduction section of this article.The research background of this article is presented.We illustrate the physical principle of luminescence and some frequently-used characterization methods for luminescent material,in which the measurement and analysis of thermoluminescence are discussed in detail.The brief survey of rare-earth elements and luminescent properties of their ionic form is provided as well.At last,we briefly describe the particular works of this dissertation.In the second chapter,a series of Pr3+/Ce3+ doped yttrium aluminium garnet(YAG)phosphors were synthesized to investigate the energy transfer between Pr3+ and Ce3+for their potential application in white light-emitting diode and quantum information storage and processing.The excitation and emission spectra of YAG:Pr3+/Ce3+ were measured and analyzed,and it revealed that the reabsorption between Pr3+ and Ce3+ was so weak that it can be ignored,and the energy transfer from Pr3+(5d)to Ce3+(5d)and Ce3+(5d)to Pr3+(1D2)did occur.By analyzing the excitation and the emission spectra,the energy transfer from Pr3+(5d)to Ce3+(5d)and Ce3+(5d)to Pr3+(1D2)was examined in detail with an original strategy deduced from fluorescence dynamics and Dexter energy transfer theory,and the critical distances of energy transfer were derived to be 7.9 a and 4.0 A for Pr3+(5d)to Ce3+(5d)and Ce3+(5d)to Pr3+(1D2)respectively.The energy transfer rates of the two processes of various concentrations were discussed and evaluated.Furthermore,for the purpose of sensing a single Pr3+ state with a Ce3+ ion,the optimal distance of Ce3+ from Pr3+ was evaluated as 5.60 A,where the probability of success reaches its maximum value of 78.66%,and meanwhile the probabilities were evaluated for a series of Y3+ sites in YAG lattice.These results will be of valuable reference for achievement of the optimal energy transfer efficiency in Pr3+/Ce3+ doped YAG and other similar systems.In the work of third chapter,the SrB4O7:Sm2+ phosphor was synthesized by high temperature solid state reaction method.The phosphor-in-glass was prepared by mixing and firing the phosphor and TeO2-ZnO glass precursor.The XRD showed that the phosphor-in-glass was in amorphous phase because of the tiny mass fraction of phosphor in glass.The emission spectrum under the 355 nm excitation was measured,and it exhibited the same characteristic emission peaks as the phosphor sample.The temperature characteristic of the SrB4O7:Sm2+ phosphor-in-glass was discussed by analyzing the lifetime of 684 nm emission at various temperatures.The relative temperature sensitivity of 5%K-1 around 573 K was obtained for the temperature dependent lifetime,suggesting the material in study is a promising candidate for temperature sensor application.After the discovery of the new-generation persistent luminescence materials based on Eu2+,there are many debates on their long-lasting mechanism.In the work of chapter four,SrAl2O4:Eu2+/Dy3' codoped and single doped samples were analyzed by optically stimulated luminescence and thermoluminescence to clarify the long afterglow mechanism involved.The phenomenon that persistent luminescence can be realized by the excitation of 475 nm laser in SrAl2O4:Eu2+,Dy3+ evidenced that the energy of Dy3+ can transfer to Eu2+ eventually in SrAl2O4:Eu2+,Dy3+' And the optically stimulated luminescence under the excitation of 980 nm both in SrAl2O4:Eu2+,Dy3+ and SrAl2O4:Eu2+ indicated that the electron traps caused by oxygen vacancies were significant for the long-lasting luminescence.The distribution of trap depth was precisely discussed as well by analyzing a series of thermoluminescence results with varying excitation temperature,and it showed the dysprosium doping introduced a shallow trap type with depth less than 0.65 eV.This work presents a clear view of the mechanism of the persistent luminescence in SrAl2O4:Eu2+,Dy3+,and could be generalized to the other analogous long afterglow materials based on Eu2+.In the research of chapter four,we accidentally found that after exciting the SrAl2O4:Eu2+,Dy3+ phosphor at temperature above room temperature(293 K)and cooling it down for a while,the thermoluminescence curve of the sample is still related to the excitation temperature.This discovery provides a new idea to us:whether the thermoluminescence curves of some materials can 'remember' the excitation temperature?In the work of chapter five,we study this issue in detail.As a result,we confirmed that after exciting the SrAl2O4:Eu2+,Dy3+ phosphor at 333 K and cooling it down to room temperature for one day,the thermoluminescence curve of the sample is similar to the sample without the cooling process.However,if the cooling time is more than one day,the peak of thermoluminescence curve will move to a higher temperature,which means a loss of the 'memory' of the excitation temperature.At the last,we present a conclusion of our works and give an outlook of their application prospects in the future.