| In daily life,industrial applications,scientific research,etc.,temperature is one of the most basic and important physical quantities,and the accuracy and routes of temperature sensing have different requirements in different fields.With the rapid development of high-tech and life sciences,temperature sensors are required to be smaller,respond faster,and have higher sensitivity.Therefore,the non-contact optical temperature sensor shows its incomparable advantages.Since Nuebert put forward the idea of applying the optical properties of luminescent materials to temperature sensing in 1937,non-contact temperature sensing based on the optical properties has become a research hotspot.In a certain temperature range,some optical properties of luminescent materials or ions have a temperature-dependent relationship,such as spectral line width,peak position,fluorescence intensity,fluorescence lifetime,fluorescence intensity ratio,and positive anisotropy.And we can use these optical properties with temperature-dependent properties to calibrate the temperature.The non-contact temperature sensing based on the optical properties of luminescent materials has many advantages such as fast temperature response,high temperature sensitivity,and high spatial resolution.So it is a research direction worthy of research and has great application potential.The research content of this thesis is the optical temperature sensing based on BaLaMgNbO6(BLMN):Mn4+,RE3+phosphors,the following is the content arrangement of this thesis:The first chapter is the introduction part,which mainly introduces the research significance of optical temperature sensing,the energy level structure and spectral characteristics of rare earth ions and transition metal ions,the spectral characterization methods of luminescent materials,and non-contact optical temperature sensing schemes.In the second chapter,we explore the optical temperature dependence of BLMN:Mn4+phosphors.In this work,we have successfully prepared BLMN phosphors doped with different concentrations of Mn4+by a high-temperature solid-state reaction.The doping concentrations of Mn4+ are 0.2%,0.4%,0.8%,and 1%,respectively.The X-ray diffraction patterns were used to characterize the structure of powder samples.In addition,the excitation spectrum and emission spectrum of the powder sample were measured at room temperature,and each spectrum was identified.Furthermore,the temperature-dependent characteristics of BLMN:Mn4+ powder samples were investigated by measuring the excitation spectra at different temperatures,and it was found that they exhibited significant temperature-dependent relationships in the temperature range from 200 K to 500 K.In order to more intuitively understand the mechanism of BLMN:0.4%Mn4+ temperature quenching effect,we show the process of thermal quenching through configurational coordinate diagrams of Mn4+ ions.Moreover,the emission peak of Mn4+ is located in the optical window of biological tissue,which provides the possibility for the application in the temperature detection of biological tissue.Therefore,BLMN:Mn4+ powder samples have potential application value in temperature sensing.In the third chapter,based on the previous work on the optical temperature characteristics of BLMN:Mn4+ phosphors,we further combined the rare-earth ion Dy3+ to study the optical temperature characteristics of BLMN:Mn4+,Dy3+dual-activators phosphors and explore the multi-mode temperature sensing.Similarly,we successfully synthesized a new type of BLMN:Mn4+,Dy3+ phosphors with dual-activators by a high-temperature solid-state reaction.The X-ray diffraction patterns were used to characterize the structure of powder samples.And the luminescence characteristics of BLMN:Mn4+,Dy3+ phosphors as a function of temperature were studied.It was found that under 355 nm excitation,the fluorescence intensity ratio I(Dy3+)/I(Mn4+)with variation of temperature is dramatic from 230 K to 470 K.The relative sensitivity reached a maximum of 1.82%K-1 at 457 K,and the thermal-quenching activation energy of Mn4+ was calculated to be 3323 cm-1.In addition,the Mn4+(2Eg→4A2g)fluorescence lifetime can also be applied to temperature sensing,and the relative sensitivity reaches a maximum of 2.43%K-1 at 437 K.the thermal-quenching activation energy of Mn4+ is 3871 cm-1.These studies show that BLMN:Mn4+,Dy3+ phosphors achieve dual-mode temperature sensing and have high relative sensitivity.In the fourth chapter,based on the dual-mode temperature measurement scheme studied in the previous work,we try to propose a 7F1 and 7F2 low-excitation thermal coupling energy level of Eu3+ temperature sensing.The temperature sensing range is widened to the low temperature region(120 K to 230 K),so that temperature sensing in the full temperature region(120 K to 500 K)is realized.In this work,we successfully synthesized BLMN:Mn4+,Eu3+ phosphors by a high-temperature solid-state reaction,and performed structural and spectroscopic analysis.Under the 394 nm excitation,the fluorescence intensity ratio I(Eu3+)/I(Mn4+)has a significant change with increasing temperature from 320 K to 500 K.The relative sensitivity reaches a maximum value of about 1.67%K-1 at 463 K,and the thermal-quenching activation energy of Mn4+ is calculated as 3130 cm-1.In order to characterize the stability of BLMN:Mn4+,Eu3+phosphors,we performed temperature cycling experiments and the result illustrates that this temperature-dependent fluorescence intensity ratio is repeatable and reversible.In addition,based on Mn4+(2Eg→4A2g)fluorescence lifetime temperature sensing,the relative sensitivity reached a maximum of 2.70%K-1 at 437 K,and the thermal-quenching activation energy of Mn4+ was 3469 cm-1,in the temperature range from 230 K to 500 K.Finally,we use the low excitation thermal coupling energy levels of Eu3+(7F1 and 7F2)to achieve temperature sensing in the low temperature region(less than 230 K).The fluorescence intensity of Eu3+(5D0→7F1)with variation of temperature is dramatic.The energy level difference between the two thermal coupling energy levels of the 7F1 ground state and the 7F2 low-excitation state is calculated to be 732.4 cm-1.The relative sensitivity SR reached a maximum of 0.55%K-1 at 290 K.All these studies show that BLMN:Mn4+,Eu3+phosphors achieve temperature sensing in the full temperature region(120 K to 500 K)through a combination of multiple temperature measurement modes and achieve good relative sensitivity,which makes the phosphors have more practical temperature sensing applications and greater application prospects.At the end of this thesis,we summarize the main content of these works and look forward to the future development direction of multi-mode temperature sensing based on dual-activators luminescent materials. |
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