Optical Temperature Sensor Based On Green Upconversion Fluorescence Of Er Ions

For the past years,optical temperature sensing based on the fluorescence intensity ratio?FIR?technique have attracted much attention.The technique is based on the comparison of fluorescence intensities of two temperature dependent emissions from closely spaced energy levels to a lower state of rare-earth ions such as Er³⁺,Pr³⁺,Yb³⁺,Nd³⁺.Two upconversion emissions ⁴S_3/2?⁴I_15/2?550 nm?and ²H_11/2?⁴I_15/2?530nm?of Er³⁺are particularly suitable for this application.In this work,we have designed an optical temperature sensor based on the thermal effect of fluorescence intensity ratio of 980-nm upconverted green 530-and550-nm emissions of Er₂O₃·3Nb₂O₅ phosphor;On the premise that the KBr itself does not affect either the Er³⁺spectroscopic characteristics or the FIR value,the KBr dilution enables to improve the signal-to-noise ratio and sensitivity of the temperature sensing that based on rare-earth ion upconverted fluorescence;The temperature characteristics of the upconverted green fluorescence temperature sensor based on Er:Yb:NaGd?WO₄?₂ nanocrystals and Er:Yb:NaYF₄ microcrystals under 980 nm laser pump were studied;The temperature characteristics of the green fluorescent temperature sensor based on Er:SrGdGa₃O₇ crystal under 488 nm xenon lamp pumped were also studied.The specific research contents and results are as follows:1.Er₂O₃·3Nb₂O₅ phosphor phase was synthesized by sintering the mixture of Er₂O₃ and Nb₂O₅ powder with a molar ratio of 1:3 at 1200??1537 K?for 76 h.Optical absorption and emission characteristics of the Er₂O₃·3Nb₂O₅ phosphor were investigated in comparison with the ErNbO₄ and Er₃NbO₇.The Er₂O₃·3Nb₂O₅phosphor shows stronger upconversion?UC?emission than the other two.Further study of temperature effect on the UC emission shows that both the peaking and integrated UC intensities decrease almost linearly with the raised temperature,and the⁴S_3/2?⁴I_15/2?560 nm?UC intensity shows a stronger temperature dependence,implying that the Er₂O₃·3Nb₂O₅ phosphor is promising for temperature sensing.2.We report an optical temperature sensor based on the thermal effect of fluorescence intensity ratio of 980-nm upconverted green 530-and 550-nm emissions of Er₂O₃·3Nb₂O₅ phosphor.The sensor consists of only a 980-nm LD,two narrow band interference filters and two Si-photocells,while being without the use of optical lens to collect the fluorescence.Thermal effect on the photocell output was calibrated.The results show that the output has a linear relation to the temperature and the linearity is independent of input power.The performance characterization shows that the sensor exhibits a relative sensitivity?5-7?×10^-3K^-1 in the temperature range of303-353 K.The setup is applicable to other Er³⁺-doped materials with a higher relative sensitivity.3.We exemplify the Er?NbO₃?₃ phosphor to demonstrate that the performance of the temperature sensor based on thermal effect of fluorescence intensity ratio?FIR?of980-nm-upconverted Er³⁺green 530 and 550 nm emissions can be improved by using KBr-diluted phosphor.The sensing performance of the diluted phosphor plate was studied as a function of KBr:Er?NbO₃?₃ molar ratio from 0:1 to 100:1.The results show that the KBr dilution enables to enhance the fluorescence intensity and increase the temperature sensitivity.Meanwhile,the KBr itself does not affect either the Er³⁺spectroscopic properties or the FIR value.There is an optimum KBr:Er?NbO₃?₃ molar ratio within 15:1 and 20:1,for which the 530?550?nm signal increases by 30%?20%?and the relative sensitivity at the physiological temperature increases by 14%.4.We report an optical temperature sensor based on the thermal effect of fluorescence intensity ratio of 980-nm upconverted green 530-and 550-nm emissions of Er³⁺-Yb³⁺co-doped NaYF₄ microcrystals or NaGd?WO₄?₂ nanocrystals.To achieve that,a simple experimental setup has been developed that consists of a 980-nm LD,a plano-convex lens,two interference filters and a Si-photocells.The performance characterization can be investigated just pumped by 15mW 980-nm laser.And it shows that the sensor based on the NaYF₄ microcrystals exhibits a relative sensitivity?10-123?×10^-3K^-1 in the temperature range of 100-350 K,and the sensor based on the NaGd?WO₄?₂ nanocrystal exhibits a relative sensitivity?8.7-107?×10^-3K^-1 in the temperature range of 100-350 K.5.We report an optical temperature sensor based on the thermal effect of fluorescence intensity ratio of 980-nm upconverted green 530-and 550-nm emissions of Er³⁺-Yb³⁺co-doped TeO₂-PbF₂ glass.To achieve that,a simple experimental setup has been developed that consists of a 980-nm LD,a plano-convex lens,two interference filters and a Si-photocells.The performance characterization can be investigated just pumped by 50 mW 980-nm laser.And it shows that the sensor exhibits a relative sensitivity?10.3-127?×10^-3K^-1 in the temperature range of 100–350 K.6.We report an optical temperature sensor based on the thermal effect of fluorescence intensity ratio of 488-nm downconverted green 530-and 550-nm emissions of Er³⁺-doped SrGdGa₃O₇ single crystal.To achieve that,a simple experimental setup has been developed that consists of a Xe Lamp,a plano-convex lens,three interference filters and a Si-photocells.The performance characterization can be investigated just pumped by 5 mW 488 nm Xe lamp.And it shows that the sensor exhibits a relative sensitivity?7.8-96.2?×10^-3K^-1 in the temperature range of100-350 K.This paper mainly have three innovative points:?1?The earlier use of photocells and filters to replace the monochromator to characterize 980-nm upconverted green fluorescence intensity ratio as a function of temperature of the erbium ion(Er³⁺)and then achieve temperature.Optical temperature sensor based on the thermal effect of fluorescence intensity ratio of 980-nm upconverted green 530-and 550-nm emissions of Er³⁺,which have small size,low cost,portable,is realized initially for the purpose of industrial production.?2?We use KBr to dilute phosphor to enhance the fluorescence intensity and increase the temperature sensitivity for the first time.?3?The temperature characteristics and upconversion mechanism of several Er³⁺doped matrix materials were studied,These kinds of matrix materials all show stronger upconversion emission,higher relative sensitivity,lower pump power and etc.