Self-reduction Properties And Optical Thermometry Of Europium Ions In Boraphosphate

Traditional contact thermometers cannot meet the demand for temperature monitoring in special and complex environments,and suffer from disadvantages such as low spatial resolution and slow response time.Therefore,it is crucial to develop non-contact optical thermometers with high sensitivity,high spatial resolution,and fast response.Currently,temperature-sensing materials based on the fluorescence intensity ratio of rare-earth luminescent materials have attracted much attention from researchers.Eu²⁺and Eu³⁺are widely used activators for rare-earth luminescent materials and their luminescence originates from 5d-4f and 4f-4f transition,respectively.The differences in fluorescence thermal quenching caused by different electron transition properties make them good activators for constructing proportional fluorescent temperature probes.More and more scholars are devoted to the study of Eu²⁺/Eu³⁺co-doped proportional temperature sensing materials,which is significant to investigate the optical properties of such materials and explore their application prospects.In this thesis,two new Eu²⁺/Eu³⁺-doped boraphosphate phosphate luminescent materials have been constructed,the structures,luminescent properties,self-reduction of activated ions and thermal quenching mechanism have been systematically studied to explore their potential applications in fluorescence temperature measurement field.The main results are as follows:1、The Ca BPO₅:Eu²⁺/Eu³⁺phosphors containing BO₄ and PO₄ structural units were designed and synthesized,the self-reduction of Eu³⁺under air conditions was successfully achieved XRD Rietveld refinement,TEM and SEM analysis were characterized.Emission peaks of Eu²⁺（402 nm）and Eu³⁺（588 nm,612 nm,653 nm,694 nm）were observed from the samples under 280 nm UV excitation,which are originating from the Eu²⁺5d-4f and Eu³⁺⁵D₀→⁷F_J（J=1,2,3,4）transition,respectively,EPR tests verified the stable presence of Eu²⁺,the self-reduction mechanism of Eu²⁺was analyzed by using charge compensation model.Temperature-dependent fluorescence spectroscopy tests were carried on a series of Ca BPO₅:x Eu²⁺/Eu³⁺（x=0-0.7）samples,it was found that the intensity of the emission peak at 402 nm decreased sharply as temperature increase,while the intensity of the emission peak at 612 nm was insensitive to temperature changes.The fluorescence intensity ratio of Eu²⁺/Eu³⁺is used for temperature measurement and the maximum absolute and relative sensitivities reach as high as 0.184 K^-1 and 3.444%K^-1,respectively.The Debye temperature,energy band structure,HRBE and VRBE electronic structure diagrams of Ca BPO₅ were studied by first-principles calculations,and the energy difference between the 5d excited state of Eu²⁺and the conduction band of the substrate was 0.48 e V,which is very close to the thermal ionization energy barrier of Eu²⁺（0.475 e V）obtained by fitting the temperature-dependent fluorescence lifetime,well explaining the thermal quenching phenomenon of Eu²⁺.2、A series of Sr BPO₅:Eu²⁺/Eu³⁺phosphors were synthesized by high-temperature solid-phase method under air atmosphere.The structural and morphological features were described by XRD,TEM,SEM and Raman spectroscopy,and the valence states of Eu ions were analyzed by XPS and EPR tests,and the self-reduction process of Eu²⁺was revealed by charge compensation model.The emission spectrum in the range of 303-573 K of the material were carried out.It was found that the fluorescence intensity ratio of Eu²⁺/Eu³⁺exhibits sensitive response to temperature,which indicated that the material could be applied to optical thermometry.Further co-doping of Li⁺ions,the emission of Eu³⁺shows obvious anomalous thermal quenching,which effectively enhanced the optical temperature sensitivity of the material,of which the maximum relative sensitivity was increased from 6.52%K^-1 to 8.23%K^-1.The successful introduction of Li⁺was demonstrated by NMR tests.The effect of introduction of Li⁺ions on defects was analyzed by thermoluminescence spectroscopy,and the results indicated that the increased deep traps might be directly responsible for the exacerbation of the Eu³⁺anomalous thermal quenching and the increase of fluorescence lifetime.