Preparation,Structure And Luminescence In Temperature Sensing Of Rare Earth Doped Oxyfluoride Glass Ceramics Containing Fluoride Nanocrystals

With the development of the Optoelectronics,growing interests have been focused on new type of optical materials because of the widely applications in industrial production and daily life.In recent years,temperature sensors based on fluorescence intensity ratio attracted a great deal of attention due to it’s simple operation,high efficiency,high accuracy and precision.Based on the above issues,oxyfluoride glass ceramics combine the merits of oxide glasses and fluoride nanocrystals.Good mechanical strength,high thermal stability and chemical durability,low phonon energy make oxyfluoride glass ceramics a good candidate for optoelectronic devices.Novel transparent oxyfluoride glass ceramics were prepared and crystal phase evolution from cubic BaF₂ to Ba_xLu_1-xF_2+xwas achieved by the gradual substitution LuF₃ for BaF₂ in the glass compositions in mol% of 65SiO₂–14.5B₂O₃–11.5Na₂O–（9–x）BaF₂–xLuF₃（x = 0,1,2,3）.The corresponding crystallization mechanism was explored according to FTIR、XRD and TEM results.The enhanced emission intensity,obvious Stark splitting in the emission spectra and long fluorescence decay lifetimes of Eu³⁺ ions evidenced the incorporation of Eu³⁺ ions into the precipitated fluoride nanocrystals.Especially,along with the gradual substitution LuF₃ for BaF₂,much more Eu³⁺ ions were partitioned into the precipitated Ba_1-xLu_xF_2+x nanocrystals,which provided a novel strategy of controlling the ionic distribution and enhancing the luminescence efficiency of rare earth ions in the oxyfluoride glass ceramics.Temperature dependent characteristics of upconversion luminescence of Er³⁺/Yb³⁺ ions in the oxyfluoride glass ceramics was investigated and a high thermal sensitivity was obtained based on the fluorescence intensity ratio（FIR）technique,which suggested that this material was a promising candidate for the optical temperature sensors.Er³⁺/Yb³⁺-codoped transparent oxyfluoride glass ceramics containing Na₅Lu₉F₃₂ nanocrystals were fabricated with the purpose of optical thermometry for the first time.Intense upconversion luminescence from Er³⁺ and Yb³⁺ ions in the oxyfluoride glass ceramics was observed by the naked eyes at a low pumping power density（0.167W/cm2）.The green upconversion luminescence dependent temperature was investigated by the fluorescence intensity ratio（FIR）between two thermally coupled levels（2H11/2 and 4S3/2）of Er³⁺ ions in the range of 323K–573K and the maximum temperature sensitivity reached to 0.0074 K-1.Low pumping power,intense upconversion luminescence and high temperature sensitivity indicates this material is a promising candidate for the applications in the optical temperature sensors.The crystal phase evolution from cubic-to-hexagonal NaYF₄ was achieved in transparent glass ceramics by the gradual substitution Na2 O for Al₂O₃ in the glass compositions in mol% of 61SiO₂–（10-x）Al₂O₃–（14+x）Na₂O–7NaF–7.9YF₃.It was found that high ratio of Na/Y and relax of the glass structure may be responsible for the precipitation of β-NaYF₄ nanocrystals.The corresponding crystallization mechanism and microstructure were explored according to CTE,XRD and TEM results.The remarkable changes of emission intensity and Stark splitting of Eu³⁺ ions verified the different behavior of Eu³⁺ during the crystal phase evolution.Efficient upconversion luminescence and sensitive temperature sensing behavior were observed and analyzed in Er³⁺/Yb³⁺ co-doped glass ceramics.