Research On Optical Fiber Tmeperature Sensors Based On Upconversion Nanocrystals

Optical fiber temperature sensors are used for accurate temperature sensing in harsh environments such as high-voltage and strong magnetic fields,strong acids and alkalis because of their advantages of accurate temperature measurement,real-time dynamic response,and anti-electromagnetic interference.Rare earth ions have abundant energy levels,and their luminous intensity is easily affected by temperature,so they are very suitable for optical temperature sensing.In recent years,the preparation technology of rare earth doped upconversion optical materials has matured,and various upconversion luminescent materials have emerged as the times require,which promotes the combination of upconversion materials and optical fiber devices.At present,devices based on upconversion luminescent materials and optical fibers have disadvantages such as cumbersome preparation and narrow temperature sensing range,and reports on the practical application of such optical fiber sensors are still lacking.Therefor,this study has done the following research.NaYF₄:Er³⁺/Yb³⁺nanocrystals and NaYF₄:Er³⁺/Yb³⁺@NaYF₄ nanocrystals were prepared by the high-temperature solvent method.The crystal structure of the samples was determined by X-ray diffractometer and the morphology of the samples was analyzed by transmission electron microscopy.The luminescence mechanism of the sample was explained according to the upconversion fluorescence spectrum of the sample.The results show that the growth of an inert layer of NaYF₄ on NaYF₄:Er³⁺/Yb³⁺nanocrystals can effectively improve the luminous efficiency.The results show that NaYF4:Er³⁺/Yb³⁺@NaYF4 nanocrystals have brighter upconversion fluorescence,which can provide brighter upconversion fluorescence in the subsequent fiber-optic temperature sensor preparation.A new point type all-optical temperature sensor device was designed and realized.With chloroform solvent,NaYF4:Er³⁺/Yb³⁺@NaYF4 nanocrystals were successfully incorporated into PDMS,and the fiber sensor were realized by dipping method.The fiber temperature sensor probe based on NaYF4:Er³⁺/Yb³⁺@NaYF4 nanocrystals was prepared by dipping method,.Nanocrystals were fixed on the fiber end surface by using PDMS as optical glue,which solved the problem of temperature-sensitive materials fall off easily during temperature measurement in the actual.This new optical fiber sensor has good spectral responsed in the range of 293—373 K.The reasults show the sensor has the greatest relative sensitivity 1.62%K^-1 at 293 K,and error is less than 0.5 K.Moreover,we also explored the stability,repeatability and universality of fiber optic sensors.By embedding the optical fiber temperature sensor inside the battery,we explored the internal temperature of the battery.The results show that the internal temperature rise of the battery is 1.9 ^oC、4.6 ^oC、10.4 ^oC、19.7 ^oC、33.9 ^oC and 52.4 ^oC at the discharge rates of 0.2C、0.5 C、1.0 C、2.0 C、3.0 C、4.0 C.In addition,the experiment also carried out real-time monitoring of the internal temperature change of the lithium battery at a 3 C discharge rate,and explore the curve relationship between battery state and internal temperature under different charge and discharge rates.The results shows that this new type of fluorescent optical fiber sensor is expected to provide a new way for the design of battery health management systems.