Study On Preparation,Structure And Optical Thermometry Of Rare Earth Doped Upconversion Luminescent Materials

With the development of temperature measurement technology,rare earth（RE）doped up-conversion（UC）temperature measurement materials have been paid more and more attention at home and abroad because of their excellent luminous performance,anti-interference,fast response and high resolution.The exploration of excellent rare-earth doped temperature measuring materials and the pursuit of high sensitivity are also the directions of many scientific researchers in recent years.In order to prepare RE doped temperature measuring materials with high sensitivity and good thermal stability,a series of RE ions were introduced into apatite-based phosphor and molybdate/niobate glass ceramics.The structure,microstructure,optical transmittance,upconversion luminescence and optical temperature measurement characteristics of the prepared material were systematically studied,providing theory and technical support for the research and development of high-performance optical temperature measurement materials.（1）Sr₂Gd₈（Si O₄）₆O₂apatite phosphors were prepared by high temperature solid state method.The effects of different rare earth combinations(Yb³⁺/Er³⁺,Yb³⁺/Tm³⁺)and concentrations on the luminescent properties were studied by fluorescence spectrum analysis,fluorescence lifetime analysis and related calculation,and possible energy transfer ways were put forward.XRD,SEM,FT-IR and Raman were used to characterize the structure of the phosphor.According to the fluorescence intensity ratio（FIR）technology,the fitting of different fluorescence intensity ratios of several emission bands was successfully realized.Among them,in the temperature range of298-623 K,the maximum relative sensitivity(S_r-max)and the maximum absolute sensitivity(S_a-max)of Yb³⁺/Er³⁺-doped Sr₂Gd₈（Si O₄）₆O₂phosphor based on thermal coupling energy level（TCEL）were 1.57 K^-1and 0.55%K^-1,respectively.The S_r-maxand the S_a-maxobtained based on the non-TCEL can reach 2.13%K^-1and 0.17%K^-1.In addition,in the range of 323-573 K,the S_r-maxand S_a-maxof Yb³⁺/Tm³⁺-doped Sr₂Gd₈（Si O₄）₆O₂phosphor based on TCEL were 2.72%K^-1and 0.49‰K^-1.And the S_r-maxand S_a-maxobtained based on the non-TCEL can reach 0.71%K^-1and 2.52%K^-1,（2）Sr₅（PO₄）₃F:Er³⁺,Yb³⁺transparent glass-ceramics（GCs）were prepared by melt quenching,heat treatment and controlled crystallization.The effects of heat treatment system on the crystal phase composition,transmittance and UC luminescence of Sr₅（PO₄）₃F GCs were studied,and the heat treatment technology of glass was explored and optimized.The structure and microstructure of glass-ceramics were characterized in detail by DSC,XRD,Raman,TEM and selected area electron diffraction technique.The UC emission process and energy transfer mechanism of Er³⁺and Yb³⁺in glass and GCs were studied by transmission spectrum,fluorescence spectrum analysis,fluorescence lifetime analysis and related calculations,combined with the calculation of absorbed photon number in the UC process.The FIR technique was used to calculate the UC luminescence temperature sensitivity of the transparent glass ceramic.In the temperature range of 303-653 K,S_r-maxis 1.26 K^-1and S_a-maxis0.31 K^-1.（3）Na Bi（Mo O₄）₂:Er³⁺,Yb³⁺transparent glass-ceramics（GCs）were prepared by melt quenching,heat treatment and controlled crystallization.DSC,XRD,Raman and TEM were used to characterize the structure of glass-ceramics.The results show that compared with glass,the luminous intensity of GC is greatly improved,and the smaller grain size of Na Bi（Mo O₄）₂in the glass matrix makes the transmittance of glass-ceramics reach more than 60%in the visible range.Using variable power spectrum calculations and linear fitting,the UC process of two-photon absorption is demonstrated,and the mechanism of energy transfer and possible ways are explained.In the temperature range of 378-703 K,the S_r-maxis 0.62%K^-1,and the S_a-maxis 1.04%K^-1.（4）Tm³⁺/Yb³⁺-doped KSr₂Nb₅O₁₅,Tm³⁺/Er³⁺/Yb³⁺-doped Ba Nb₂O₆and Tm³⁺/Ho³⁺/Yb³⁺-doped Na Sr₂Nb₅O₁₅transparent GCs were prepared by melt quenching,heat treatment and controlled crystallization.The structure and micro morphology of the GCs were characterized by DSC,XRD,Raman and TEM,and the corresponding phonon energy were estimated.The transmittance was measured by transmission spectrum and its optical band gap was calculated.In Tm³⁺/Yb³⁺-doped KSr₂Nb₅O₁₅GCs,the energy transfer mode and luminescence process between Yb³⁺and Tm³⁺were studied by fluorescence spectrum analysis,fluorescence lifetime analysis and related calculation.The S_r-maxcan reach 2.01%K^-1and the S_a-maxcan reach 10.1%K^-1by taking advantage of the larger thermal coupling energy level（TCEL）of Tm³⁺ions and the opposite temperature dependence.For Tm³⁺/Er³⁺/Yb³⁺-doped Ba Nb₂O₆transparent glass ceramics,the UC luminescence process and energy transfer mechanism between Tm³⁺/Er³⁺/Yb³⁺are described in detail.The multi-ratio temperature measurement strategy is realized by using FIR fitting of double emission centers and different emission bands,and the S_r-maxand S_a-maxare 2.30%K^-1and 6.71‰K^-1,respectively.For Na Sr₂Nb₅O₁₅doped with Tm³⁺/Ho³⁺/Yb³⁺,the doping substitution of Tm³⁺/Ho³⁺/Yb³⁺ions was proved by Rietveld analysis of XRD,fluorescence spectrum analysis and fluorescence lifetime calculation.The luminescence process and energy transfer path of UC were studied,and the phenomenon of different emission intensity of each emission band was explained.The multi-ratio thermometry strategy was realized by using the double emission center and the FIR fitting of different emission bands to obtain the maximum S_r-maxand S_a-maxwere 2.00%K^-1and 3.05‰K^-1,respectively.In addition,the dielectric,ferroelectric and electric energy storage properties of Na Sr₂Nb₅O₁₅transparent GC were preliminarily explored.The results show that under the voltage of 600 k V/cm,the actual discharge energy density is 1.15 J/cm³,the ultrafast discharge rate is less than 15.8 ns,and the instantaneous discharge power density reaches 225.3 MW/cm³.The Na Sr₂Nb₅O₁₅glass ceramic not only enriches the material types of multi-scale self-reference optical temperature sensors,but also is a new transparent photoelectric energy storage material.