Investigation Of Er³⁺ Ions Doped Glass And Glass Ceramic For Optical Thermometry

Compared with traditional temperature sensor,a new non-contact temperature sensor,optical thermometry,has attracted growing interests for possessing superior properties such as high sensitivity,rapid response time,immunity to harsh environment.Notably,benefited from self-calibrated and high reliability,a FIR technique related to rare earth ions has been widely applied to determine temperature and regarded as a promising way for optical thermometry.In the text,we conducted a systematic and in-depth research on rare earth ions doped amorphous thermometer materials which include glass,glass ceramic and optical fiber.The research factors are related to rare earth concentration,local environment phonon energy,crystal field,thermal effect induced by light source,and so on.It will play an important role in promoting the controllable design?optimization and application of optical temperature sensing materials.The contents and conclusions of research are presented as follows:?1?Exploration on influence factors of temperature sensitivity of glass materials:The thermally coupled energy level of rare earth ions has no relation with the doping concentration,but is related to the local environmental phonon energy.In the tellurite glass matrix,the relative sensitivities were studied by only changing the rare earth ions molar concentration(Er³⁺is 0.5,1,1.5 respectively),it was found that the slopes of fitted lines about natural logarithmic FIR as a function of inverse absolute temperature are nearly unchanged,which are 1001.4±18.8,996.5±11.8,1017.2±26.3 respectively,the result indicates that their thermally coupled energy level is not affected by rare earth ions concentrations,as a result,the maximum relative sensitivities of glass with different doping concentrations keep consistent.However,when the relative sensitivity of tellurite and corresponding fluorotellurite glass was studied by only making F^-substitute O^2-,it was found that the thermally coupled energy of Er³⁺in fluorotellurite is slightly larger than that in tellurite glass,which is about 642.9 cm^-1and 625.2 cm^-1 respectively.Based on the material components by using single variation rule,we ascribed this difference to the change in the phonon energy of the local environment where the rare earth ions are located.Subsequently,we also investigated the relative sensitivity of tellurite glass and germanate glass by only changing the network former,The result showed that the thermally coupled energy of Er³⁺in tellurite glass is significantly larger than that in germanate glass,they are approximately 695.5cm^-1 and 638.2cm^-1,respectively.Since the vibrational energy of TeO₂ is lower than that of GeO₂,therefore it further confirms the conclusion that the thermally coupled energy level of rare earth ions is related to the phonon energy of its local environment.?2?Optical thermometry comparison between glass and correspond glass ceramic:Compared with precursor glass,the upconversion luminescence intensity of glass ceramic enhanced enormously while the temperature sensitivity decreased to a certain extent after crystallization.In order to ensure the controllable crystallization and enough upconversion,we determinedthecompositionsofprecursorsilicateglasswith50SiO₂-20Al₂O₃-30CaF₂-YbF₃-ErF₃.The glass and transparent CaF₂ glass ceramic were fabricated by melt quenching method and thermal treatment.In terms of upconversion emissions,it was found that the upconversion luminescence intensity of CaF₂ glass ceramic enhanced enormously compared to that of Glass.Importantly,the temperature-dependent upconversion fluorescence intensity ratio of Glass and GC were investigated from 303K to 573K under the 980nm laser with the constant pumping power,it was found that CaF₂ glass ceramic shows weaker optical thermometry ability than precursor glass in terms of temperature sensitivity,the maximum relative sensitivity of CaF₂ glass ceramic reached to 10.6 10^-3 K^-1 at 303K while that of glass is 11.15 10^-3 K^-1 at 303K,the thermally coupled energy gap reduced about 34.2cm^-11 after crystallization,we attribute this change to the J mixed effect of crystal field.Furthermore,the FIR value variation of Glass shows weaker pumping power dependence than GC in terms of thermal effect induced by laser when the pumping power increased from 100mW to 900mW,in another word,the upconversion emission in CaF₂ glass ceramic is easier to be affected by thermal effect induced by light source when compared with precursor glass under the same condition.Finally the temperature-cycle measurements about glass and glass ceramic were conducted,the result of which suggest that both them exhibit favorable thermal stability.?3?Investigation on optical fiber thermometer based on low phonon energy matrix:the uncrystallized and well-structured fluorotellurite fiber was successfully fabricated by rod-in-tube method,whose temperature sensitivity is also relatively high.And a corresponding optical fiber temperature measurement device scheme was proposed.Based on bulk fluorotellurite cladding glass and core glass prepared by melt-quenching method,the uncrystallized and well-structured fluorotellurite fiber was successfully fabricated with machined preform by rod-in-tube method,Strong green upconversion emissions were observed under 980nm laser excitation both in precursor core glass and fiber.The characterization of thermal analyzation demonstrated this glass possessed a good thermal stability and high glass transition temperature,which greatly contribute to the process of drawing fiber and enlarging the work temperature range of optical fiber thermometer.Subsequently the analysis of temperature sensitivity about precursor glass shows that the thermally coupled energy level of Er³⁺in glass is 658.9cm^-1,and the maximum relative sensitivity is 9.09×10^-3K^-1 at 323K,which is superior most reported Er³⁺doped glass materials,as the temperature further decreases,it still exhibits a increasing tendency.We also analyzed the temperature sensitivity of fluorotellurite fiber,the result showed the thermally coupled energy level of Er³⁺in glass is 654.2cm^-1,which is consistent with that in the precursor core glass,it indicates that the relative sensitivity will not change after a process of drawing fiber.However there is a difference between the precursor core glass and fiber in the aspect of maximum absolute sensitivity,they are 2.38 10^-33 K^-1at 513K and 4.12×10^-3 K^-1 at 543K respectively,we ascribed the difference to the different preparation processes.Finally based on the prepared fluorotellurite fiber,we proposed a set of temperature measurement device with a view of practical application,in which the most important point is to make the fluorotellurite fiber matches well with the modern optical fiber communication system by means of optical fiber connector or manually docked and then sealed,this system make the fluorotellurite fiber show great potential for application in the remote temperature measurement automatically.