Preparation And Spectral Properties Of Rare Earth Upconversion Luminescent Materials For Optical Temperature Sensors

Recently,rare earth ion(Ln³⁺)co-doped upconversion?UC?luminescence materials applied in temperature sensors has attracted much attention because of the dependence of spectral properties and temperature.Compared to traditional thermometers such as glass thermometers,thermocouple thermometers,semiconductor thermometers,spectral temperature sensors have the advantages of non-contact and high sensitivity.The rare earth Er³⁺ ions was introduced into the different matrix hosts due to the characteristics of the thermocouple energy applied to the fluorescence intensity ratio?FIR?technique.In this paper,rare earth doped upconversion materials with different matrix hosts were synthesized by different synthetic methods.The luminescence and thermal properties of Er³⁺ ions in different matrix hosts were studied by fluorescence intensity ratio?FIR?.Lu₂Ti₂O₇:Yb³⁺/Er³⁺(LTO:Yb³⁺/Er³⁺)nanofluorescence powders with different Yb³⁺(Er³⁺)doping concentrations were prepared by microwave hydrothermal method.Concentration dependent studies revealed that the optimal composition was realized for the 12 at% Yb³⁺ and2.0 at% Er³⁺-doping concentration with the strongest green upconversion emission.In the temperature range of 298-573 K,the temperature characteristics of the fluorescence intensity ratio?FIR?of the two green upconversion emission bands located at 523 nm and 545 nm at the emission center under the 980 nm excitation were investigated.The optimum sensitivity is about 31.30 ? 10^-4 K^-1 corresponds to the temperature of 536 K.This indicates that LTO:Yb³⁺/Er³⁺ nanophosphor has potential applications in optical temperature sensors.NaGd?WO₄?₂:Yb³⁺/Er³⁺microcrystals codoped with Yb³⁺?12-24 at%?and Er³⁺ions?1-10at%?were synthesized by hydrothermal process.The optimum doping concentrations of Er³⁺and Yb³⁺ for the highest emission intensity were determined by using photoluminescence?PL?analyses.Concentration dependent studies revealed that the optimal composition was realized for the 20 at% Yb³⁺ and 6 at% Er³⁺-doping concentration with a strong green emission.The temperature dependence of the fluorescence intensity ratios?FIR?for the two green UC emission bands peaked at 532 and 554 nm were studied and the maximum sensitivity is approximately 114.96?10^-4 K at 453 K.The results show that NGW:Yb³⁺/Er³⁺ microcrystalline phosphor can be used in optical temperature sensor.The Yb³⁺-Er³⁺-Y3+tri-doped cubic ZrO₂?brief as YSZ:Yb/Er?nanophosphors withdifferent Yb³⁺(Er³⁺)doping concentrations have been prepared by microwave hydrothermal method followed by further calcining treatment.X-ray diffraction?XRD?,transmission electron microscope?TEM?,and photoluminescence spectra were used to characterize the properties of YSZ:Yb/Er nanophosphors.Concentration dependent studies revealed that the optimal composition was realized for the 15 at% Yb³⁺and 1 at% Er³⁺-doping concentration with a strong pure red emission.The temperature dependence of the fluorescence intensity ratios for the red UC emission bands peaked at 655 nm and 679 nm(⁴F_9/2?⁴I?15/2? stark energy level splitting)was studied.The results showed that the sensitivity of the samples in 37 K reached a maximum of 81.50?10^-4 K^-1 which indicate that YSZ:Yb/Er nanophosphors could be a promising biological labeling material and temperature sensing material.Gd₂TiO₅:Yb³⁺/Er³⁺?brief as GTO:Yb/Er?phosphor was synthesized by sol-gel method.The upconversion luminescence color was adjusted by changing the Yb³⁺ ion doping concentration.The temperature dependence of the fluorescence intensity ratios?FIR?for the two green UC emission bands peaked at 524 nm and 546 nm and the red UC emission bands peaked at 648 nm and 678 nm?4F9/2?4I15/2 stark energy level splitting?of the different Yb³⁺ions doped with GTO:Yb/Er phosphors were studied.The results show that the sensitivity of green light decrease with the increase of Yb³⁺doping concentration,while the sensitivity of red light temperature increases with the increase of Yb³⁺ doping concentration,and the sensitivity of green and red light is 2 at% Yb doping reaches a maximum of 40.76×10^-4 K^-1and 18 at% Yb doping to a maximum of 16.59×10^-4K^-1,respectively.