Study On Surface Corrosion And Temperature Sensitivity Characteristics Of Upconversion Microcrystals

Traditional thermometers have been unable to meet the temperature measurement requirements of emerging fields such as micro nano devices and precision medicine.In recent years,fluorescence temperature measurement technology based on up conversion micro nano materials has attracted extensive attention.The fluorescence intensity ratio（FIR）of the thermally coupled energy level of up conversion fluorescent materials is sensitive to the change of external temperature;The upconversion crystal based on micro nano scale can realize accurate temperature measurement from small to nano scale,and can meet the temperature measurement requirements in the fields of micro nano optoelectronic devices,biological cells and so on.The main research content of this paper is to explore the optical temperature sensitivity of lanthanide double doped single upconversion microcrystals,establish the qualitative and quantitative relationship between fluorescence intensity ratio fir and temperature,and clarify the influence mechanism of surface corrosion on the fluorescence characteristics and temperature sensitivity of single upconversion microcrystals.The main contents of the research are as follows:（1）Hydrothermal method can control the preparation of lanthanide double doped upconversion single microcrystals,and study the effects of acid corrosion of different intensities such as hypochlorous acid,citric acid,acetic acid,phosphoric acid and hydrochloric acid on the morphology and optical properties of micron crystal surface.Under the same reaction time,p H value and stirring speed,the morphology and fluorescence produced by various acid corrosion are obviously different.Among them,the microcrystal corroded by hypochlorous acid,citric acid,acetic acid and hydrochloric acid,with the decrease of p H value of acid,the depth of Surface Nanostructure continues to increase,and the overall morphology of single crystal is still hexagonal.Different from the microcrystals corroded by hypochlorous acid,citric acid,acetic acid and hydrochloric acid,the upconversion crystallites corroded by phosphoric acid show angular hexagonal rings.（2）The temperature sensitivity and stability of the intensity ratio（FIR）of the green emission peak（520nm/540nm）of two thermally coupled energy levels(Er³⁺:²H_11/2 and ⁴S_3/2)of a single upconversion microcrystal were studied.The single upconversion microcrystalline temperature measurement sensitivity has good reproducibility when the temperature increases and decreases（deviation<1.0%）.Importantly,the temperature measurement sensitivity of single upconversion microcrystals with corrosion on the surface based on fir（520nm/540nm）is almost the same as that of microcrystals without corrosion on the surface（deviation<3.3%）,indicating that the influence of surface defects on the temperature measurement sensitivity based on fir（520nm/540nm）can be ignored.The effect of surface corrosion on the fluorescence characteristics of single upconversion micro crystal was studied.When the temperature was reduced from 415k to 301k,the slope of Ln（FIR）and 1/T of 650nm and540nm of corroded micro crystal increased by 138.9%compared with that of 650nm and 540nm of non corroded micro crystal.It is proved that the introduction of surface defects can effectively adjust the up conversion process.（3）The temperature sensitivity and reproducibility of hexagonal ring microcrystals were studied,and compared with other microcrystals with different corrosion morphology,and the mechanism of the difference of optical properties was described.Single citric acid deeply corroded flowerβ-Na YF₄:Yb³⁺,Er³⁺microcrystals have good reproducibility of temperature measurement sensitivity with the increase and decrease of temperature（deviation<1.7%）;Single hexagonal ring during the temperature increases and decrease ofβ-Na YF₄:Yb³⁺,Er³⁺microcrystals,the temperature measurement sensitivity also has good reproducibility（deviation<3.8%）.At the same time,hexagonal ring microcrystals show almost the same temperature measurement sensitivity as other microcrystals with different corrosion degrees.This further shows that various corrosion conditions lead to significant changes in the morphology of upconversion microcrystals and attenuation of luminescence intensity to a certain extent,but the effect on the temperature measurement sensitivity based on fir（520nm/540nm）is negligible.It is worth noting that the red（650nm）and green（540nm）ln（FIR）and 1/T slopes of the ring micro crystal are slightly higher than those of the up conversion micro crystal without corrosion,shallow corrosion and deep corrosion（about 28%）,which further indicates that the introduction of surface defects can effectively adjust the up conversion process,especially the ring structure,which has greater potential in temperature sensitivity monitoring performance to be discovered and studied.This paper focuses on the surface corrosion and temperature measurement performance of up conversion microcrystals,which is of great significance in promoting the application of cell temperature measurement and MEMS temperature measurement.