Study On Yb³⁺/Tm³⁺Codoped YAG Or Y₂O₃ Single Crystal Fiber Upconversion Fluorescence Temperature Sensing Technology

In recent years,the fluorescence intensity ratio thermometry based on the rare earth ions upconversion fluorescence intensities of two thermally coupled levels,has attracted much attention due to its high sensitivity and the simple working principle.The upconversion fluorescence temperature sensing technology based on Yb3+/Tm3+codoped YAG or Y2O3 single crystal fiber was studied in this paper.Yb3+/Tm3+ end-codoped YAG or Y2O3 single crystal fibers were successfully grown by laser heated pedestal growth(LHPG)method.The samples are 5.0%Yb3+/0.5%Tm3+:YAG(1#),5.0%Yb3+/1.5%Tm3+:YAG(2#),5.0%Yb3+/0.5%Tm3+/0.5%Pr3+:YAG(3#)and 5.0%Yb3+/0.5%Tm3+:Y2O3(4#).The affecting factors of the fluorescence intensity ratio based on those thermal coupled levels was analyzed by studying the concentration of doped ions,the upconversion fluorescence intensities and the temperature characteristics.And the results are shown below.(1)By analyzing the upconversion spectra,it is found that Yb3+/Tm3+ doped Y2O3 matrix has a higher upconversion emission efficiency,compared with the same ions concentration doped YAG host material under the same pump excitation intensity.And the higher the concentration of Tm3+,the stronger the red upconversion fluorescence to the same matr:ix.(2)By studying the upconversion temperature characteristics of these sample,it was concluded that the 3F2,3,3H4 levels,3H4(a),3H4(b)levels and 1G4(a),1G4(b)levels are the thermally coupled levels in Yb3+/Tm3+:YAG;3F2,3,3H4 levels and 1G4(a),1G4(b)levels are the thermally coupled levels in Yb3+/Tm3+:Y2O3.Through the analysis of these samples,it is shown that the concentration of Tm3+ ions and host materials have no influence on the energy gap of the thermally coupled levels,but the fluorescence intensity ratio will be affected by the ions concentration and the matrix material.(3)It was found that the higher relative sensitivity with the value of 2571.36/T2 can be obtained,based on the thermal coupled levels of 3F2,3 and 3H4 in Tm3+ doped sample 1#.By analyzing the absolute sensitivity,it should be used the fluorescence intensity ratio based on the Tm3+ions of the thermal coupled levels of 1G4(a),1G4(b)to obtain the higher absolute sensitivity,in the temperature range below 450K.When the temperature is higher than 450K,the fluorescence intensity ratio based on thermal coupled levels of 3F2,3 and 3H4 should be used as the measuring principle.(4)The fluorescence intensities ratio of the samples at different laser excitation intensity were studied.Using the fluorescence intensity ratio based on a pair of Stark split thermal coupled levels can eliminate the problem from the different value of fluorescence intensity ratio due to different laser excitation intensity,in a certain temperature range.