Er³⁺/Yb³⁺ Co-doped Tellurite Glasses For Optical Fiber Temperature Sensor

Compared with conventional measurement method,optical fiber temperature sensors have more advantages of highly accuracy,dynamic response,corrosion resistance and immunity to electromagnetic,especially for the temperature measurements of harsh environment?such as high current and high magnetic field,etc.?.Since the optical fiber temperature sensor based on fluorescence intensity ratio?FIR?technique was firstly reported in 1990,it has attracted great attention.Especially,it had attracted great attention due to its simple structure,convenient data processing and high sensitivity.FIR technique is based on the large variation of the relative fluorescence intensities from two thermally-coupled energy levels of rare earth ions,which correspondence with environmental temperature changes.Tellurite glass is a kind of heavy metal oxide glass with high solubility and refractive index,low phonon energy,good chemical stability,wide infrared range,which expected to be excellent glass matrix.Owing to the special electronic structure,rare earth ions have excellent optical properties for optical temperature sensor.While the research mainly limits to the basic experimental study,so how to turn it into practical fiber temperature sensor become a major scientific problem.This paper explored the synthesis and carried on luminescent properties of Er³⁺/Yb³⁺co-doped tellurite glasses for optical fiber temperature sensor,and designed a point single mode all-fiber temperature sensor in order to solve the application:1.Er³⁺/Yb³⁺co-doped tellurium-zinc-niobium glass were synthesized by conventional melt-annealing method.We changed the ratio of TeO₂/ZnO,result shows that the glass transition temperature?T_g?of the tellurite does not change significantly with the increase of the TeO₂/ZnO ratio,but the temperature at the starting point T_x and the crystallization peak temperature T_p increases obviously,and the thermal stability is improved obviously.When Zn O content reach 10mol%,?T was maximum.Raman spectrum show that there is no significant change in the maximum vibrational peak,and the phonon energy of the matrix does not change obviously.However,the ratio of TeO₂/ZnO will bring about the change of the structure.The low content of ZnO will promote the transformation of[Te O₃]^4-to[TeO₄]^4-.We analyzed the influence on the temperature sensing performance of the samples.The emission intensity was measured and strong green upconversion luminescence can be observed.Results show that the sensitivity of the system was 0.0052K^-1,0.0053K^-1,0.0060K^-1and 0.0065K^-1 with the ratio of TeO₂/ZnO increased.2.Er³⁺/Yb³⁺co-doped tellurium-tungsten-lanthanum glass were investigated by conventional melt-annealing method with same ratio of doping content but different concentration on Er³⁺/Yb³⁺.It was to be found that the samples have good thermal stability with T_g in 475?,and it can ensures high working temperature sensing application.Raman spectra shows that[TeO₃]^4-in 754cm^-1 is stronger than[TeO₄]^4-in678cm^-1,which is favorable for upconversion luminous intensity.Results shows that the sensitivity of the system were 0.0050 K^-1?0.0073 K^-1?0.0078 K^-1?and 0.0090K^-1with high doping content.Temperature sensor performance shows that higher concentration will make the thermal distribution more effective than the non-radiative relaxation,which will make contribute to the improvement of the sensing sensitivity.3.A point single mode all-fiber temperature sensor was developed and the temperature sensing characteristic was studied.The sensing probe was fabricated by the fiber dip coating technique with innovative protection design for optical glue as protective shell.This makes the sensing probe have excellent stability.With this condition,the sensing probe can reach a higher sensitivity for the large difference of the thermal expansion coefficient between tellurite glass and quartz fiber.The fiber temperature sensor can be observed bright green upconversion under 980nm laser pump with 1mW power.The temperature sensing characteristics of the sensing probe was studied by establishing the ratio of the fluorescence intensity ration of ²H_11/2 and⁴S_3/2 based on Er³⁺.Results show that the fiber optic temperature sensing device has the advantages of portable,low cost and high sensitivity,and it is expected to be applied to the actual temperature measurement.Finally the paper covers all results of this dissertation have been concluded.And we points out the deficiencies of this work and works needed to be done.