Local Structure And Luminescent Temperature Properties Of Mn²⁺ And Eu³⁺ Ions Doped Oxysalts

We carried out the preparation and characterization of materials based on the general luminescent law of solids doping.The spectra-based local structure analysis and the application of materials in temperature sensing were performed.It provided a basis for investigating the performance of new luminescent materials and the application of temperature sensing.The specific research system covered the Mn2+ and Eu3+ activated oxysalts.The main research contents and results were listed as follows.In chapter 1,we First introduced the definition,classification and performance parameters of luminescence.Secondly,the configuration coordinate model,energy transfer mechanism and energy tiransfer theory were discussed.Then we presented the rare-earth ions,transition-metal ions and effects of crystal field on ion energy levels.Finally,the employed X-ray photonelectron spectroscopy(XPS)technology in the experiment was briefly introduced.The second chapter is the study of luminescence properties for Zn2GeO4:Mn2+material and its thermal quenching mechanism.Different Mn2+ concertrations doping Zn2GeO4 phosphors were synthesized via the high temperature solid state reaction.Systematic investigations were performed using X-ray powder diffraction,diffuse reflectance spectroscopy,photoluminescence spectroscopy,temperature dependence of photoluminescence spectra,X-ray photoelectron spectroscopy and afterglow decay curve.We elaborated the luminescence and thermal quenching mechanisms arising in optical excitation of the investigated samples.We attributed the green emission of Zn2GeO4 host to the radiative transition from the shallow donor levels(Znzr and Vo)to the acceptor levels(VG,and VZn),whereas the blue emission of Zn2GeO4 is due to the recombination of electrons from the local defect level of shallow donor centers with holes at the VB.The green emission of Mn2+ doped Zn2GeO4 powder is due to the d-d transition from the first excited state of 4Ti(G)to the ground state of 6A1(S).The concentration optimization of Mn2+ luminescence was performed,and 2%Mn2+ was found to have the strongest green light emission.The thermal stability and quenching of Zn2GeO4:2%Mn2+ samples were analyzed by using the temperature dependent emission spectra and the calculation results of the first principle.Thermal luminescent quenching of Mn2+ is proposed to be due to the delocalized process of excited electrons from excited state to ionized state.Finally,the detailed luminescence mechanism for photoluminescence and long persistent luminescence is demonstrated,and the corresponding energy level and transition process diagram were given.This may contribute to the understanding and optimization of luminescent properties for other Mn2+ doped inorganic phosphorsOn the basis of the experimental results in chapter 2,we further explored the application value in temperature sensing of Zn2GeO4:Mn2+ material.In chapter 3,we introduced the application of temperature imaging for Zn2Ge44:Mn2+ material based on the time resolution technic.Temperature dependencies of emission intensity and decay lifetime of Mn2+ doped Zn2GeO4 phosphor in the range from 250 K to 420 K were investigated.The relative sensitivity for sensing modal of emission intensity and decay lifetime reaches the maximum of 4.5%K-1 and 4.6%K-1,respectively.We proposed a new temperature sensing protocol based on time resolved technique.The relative sensitivity can reach the maximum of 11.8%K-1 and the best temperature resolution is about 0.65 K.Adopting the temperature measuring system,we realized monitoring the change of a micro circuit temperature distribution on printed circult board.Temperature imaging with high spatial and temperature resolutions were successfully performed in this work.In chapter 4,the main content is the research of the local structure and temperature dependent photoluminescence of Ca3Ga2Ge3O12:Eu3+ material.A series of concentrations of Eu3+ activated garnet type Ca3GazGe3O12 phosphors were successfully prepared by solid state reaction.Under the excitation of 394 nm,the phosphors show unusual red emission from 5D0 →7F4 transition of Eu3+.The emission intensity of the phosphors gradually increases with the concentration of Eu3+,and decreases from the quenching concentration of 10 mol%.Through the analysis of crystal structure,the enhancement of 5D0 →7F4 transition is due to the distortion of Eu3+ site in the crystal.It can be seen that,there is a large angle twist between the upper and lower sides of the hexahedron,resulting in the inhibition of 5D0 → 7F4 in a certain degree,while 5D0→ 7F4 transition is enhanced.Under the excitation of 610.8 nm pulse laser,the Eu,U ions populated on the 7F2 level are excited to the 5D0 level,so that the number of populations is dependent on the temperature,thus generating the temperature dependent luminescence characteristics.The intensity of 5D0→7F4 transition increases monotonously as the temperature rises in the range of 160-360 K when excited by 610.8 nm pulse laser.The temperature measurement relative sensitivity maximizes 3.66%K-1 at 160 K and keep in 1.04%K-1 at 300 K,which is determined by the variation of intensity.It is indicated that our prepared sample has good temperature sensing performance and can be applied to the field of optical temperature detection.The research in chapter 5 mainly focuses on the analysis and identification of CaTiO3:Eu3 samples with different Ca/Ti ratios based on spectra and X-ray photoelectron spectroscopy.Un-doped and 1%Eu3+ ions doped CaTiO3 samples with different Ca/Ti ratios were synthesized using solid-state reaction method.Measuring results of X-ray powder diffraction patterns,unit-cell parameters and X-ray photoelectron spectroscopy show that Eu3+ ions enter into the Ca2+ site.The high-resolution photoluminescence spectra of Eu3+ ions at 20 K in all samples did not witness a significant change under the excitation at different wavelength,implying that Eu3+ions occupy only one type of site.Considering the small spectral splitting range of 5D0+7F2 transition and the large intensity ratio of 5D0→7F2/5D0→7Fi,it can be concluded that Eu3+ occupies the 12-coordinated Ca2+ site without inversion symmetry rather than Ti4+ site.Changing the Ca/Ti ratio doesn’t affect the site occupancy of Eu3+ions in our research.These results may help clarifying the site occupancy of rare-earth ions,and optimizing the performance of rare earth doped perovskite materials.The temperature dependent luminescent characteristics of Yb3+-Er3+ codoped K2GdF5 material were discussed in chapter 6.K2GdF5:18%Yb3+,2%Er3+ sample was synthesized by solid state reaction,and the results of X-ray powder diffraction pattern was analyzed to show that the well-crystalized sample was successfully synthesized.The investigations on the possible upconversion(UC)processes and mechanism indicate that both the green and red emissions are two-photon processes and the energy transfer from Yb3+ to Er3+ plays an important role in UC process.The thermal behavior of green emissions originating from 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2 transitions was investigated in the temperature range from 307 K to 570 K.The relationship between the fluorescence intensity ratio and temperature is well-fitted with an effective energy gap of 690 cm-1.The relative sensitivity of the sample reaches the maximum 1.1%K-1 at 307 K.The results indicate that the present UC sample could be used as a promising candidate for optical temperature sensor.At last,the main content of this thesis were summarized and prospected.