On The Relative Sensitivity And Anti-interference Of Rare Earth-based Luminescence Intensity Ratio Thermometry

Fast,accurate and even non-invasive thermal sensing is a significant issue in a broad spectrum of fields.Among the various temperature measurement principles,the luminescence intensity ratio(LIR)technology has attracted much attention because of its non-invasive working pattern,strong anti-interference,excellent spatial resolution,fast response and relatively low-cost measuring device.However,there is a remaining problem for this technology,that is,low relative sensitivity(S_r).The dissertation here is aimed to solve these fundamental physical problems,focusing on the S_r and anti-interference of LIR thermometry.The upper threshold of thermally coupled states(TCS)was studied.The²H_11/2-⁴I_15/2 and ⁴S_3/2-⁴I_15/2 of Er³⁺were studied as a function of temperature,and the results showed that the populations of the ²H_11/2 and ⁴S_3/2 states spaced by the gap of?1300 cm^-1 follow the Boltzmann distribution and their S_r at 303 K is 1.51%K^-1,the maximum reported so far for the ²H_11/2 and ⁴S_3/2 based LIR thermometry.The⁴G_11/2-⁴I_15/2and ²H_9/2-⁴I_15/2 of Er³⁺were studied as a function of temperature,and they were confirmed to be TCS although their energy gap is up to 1450 cm^-1.Their S_r at 303 K is 2.05%K^-1,the largest value for the LIR thermometry on the basis of the ⁴G_11/2 and ²H_9/2 states.The ⁴F_7/2 and ⁴S_3/2 states of Er³⁺and the ⁴G_11/2 and ⁴F_9/2states of Dy³⁺were confirmed to be thermally coupled for the first time.Their gaps are 2160 and 2551 cm^-1,respectively.The ⁴F_9/2 and ⁴I_9/2of Er³⁺were studied as a function of temperature.The populations of these two levels also follow the Boltzmann distribution at high temperatures.The energy gap between the ⁴F_9/2 and⁴I_9/2 states is up to 2767 cm^-1,exceeding the maximum empirical threshold of 2000cm^-1.The S_r of the case where there is a non-exponential term in the fitting function was studied.The ³F_2,3-³H₆ and ³H₄-³H₆ transitions of Tm³⁺were investigated as a function of temperature.It was found there was a non-exponential term in the fitting function,making the practical S_r deviate largely from the theoretical expectations at low temperatures.In this case,the variation and calculati on of S_r were proposed.The S_r of the ⁴F_7/2 and ⁴S_3/2 states as well as the ⁴I_9/2 and ⁴I_11/2 states of Er³⁺were studied,further proving the accuracy of the above-mentioned expression of S_r.The LIR between the ⁵D₁-⁷F₁ and ⁵D₀-⁷F₁ of Eu³⁺was studied as a function of temperature,the S_r of which was found to increase first and then decrease,with the presence of maximum.The way to search for the temperature range corresponding to the maximum S_r was proposed.Finally,the phenomenon that the S_r first increased and then decreased with a maximum value at a certain temperature should be ascribed to the competition between thermally coupled effect and non-thermally coupled effect.The way to boost the S_r of LIR thermometry was studied.It reveals that two emission bands with totally different temperature response can boost the S_r of LIR thermometry.A dual-excitation single-emission method depending on the red-shift of the charge transfer band of WO₄^2-with the rise of temperature was proposed,and its S_r at 783 K is 4.4 times that of the ²H_11/2and ⁴S_3/2 levels of Er³⁺.The excited state absorption of Tb³⁺was disclosed and based on this mechanism the typical green emission increased with the rise of temperature.Taking this effect with the thermal quenching of the red emission of Eu³⁺together,a new LIR thermometry was proposed,whose S_r at 610 K is as large as 2.02%K^-1,exceeding that of the ²H_11/2and ⁴S_3/2 levels of Er³⁺by more than one order of magnitude.The limit of the conventional LIR temperature measurement method to increase its S_r was analyzed,and it was ascribed to thermal quenching.In order to solve the problem,here an emission band,namely the 800 nm NIR emission of Er³⁺,which increased sharply with the rise of temperature,was found,providing a choice for designing highly sensitive LIR thermal sensing at high temperatures.Anti-interference LIR thermometry was investigated.The ²H_11/2-⁴I_15/2and⁴S_3/2-⁴I_15/2 transitions of Er³⁺were selected to show the influence of emitting mode on their thermomertry property.Upon excitation at 980 nm,Er³⁺can emit green luminescence via up-conversion way.Upon excitation at 405 nm,Er³⁺can emit green luminescence via down-conversion way.The S_r of the ²H_11/2-⁴I_15/2and⁴S_3/2-⁴I_15/2 transitions is,however,free from the influence of emitting mode.The²H_11/2-⁴I_15/2and ⁴S_3/2-⁴I_15/2 transitions of Er³⁺were also selected to show the influence of interference light on their thermomertry property.When there was interference external white-LED,the LIR thermometry of the ²H_11/2-⁴I_15/2and⁴S_3/2-⁴I_15/2 transitions of Er³⁺was affected seriously,with a temperature error up to18 K at 483 K.In contrast,the ⁴G_11/2-⁴I_15/2 and ²H_9/2-⁴I_15/2 transitions of Er³⁺showed strong anti-interference feature as they escaped largely from the emitting spectrum of white-LED.A strategy of segmentation fitting was proposed to measure temperature,which could effectively reduce temperature measurement error.The physical mechanism behind this strategy was found to be attributed to the competition between the populated and de-populated processes.