Synthesis And Temperature Measurement Properties Of Rare Earth Doped Niobate Nano-phosphor

As one of the key parameters of thermodynamics,the accurate measurement of temperature plays a vital role in daily life,scientific research and biomedicine.Fluorescence temperature measurement based on fluorescence intensity ratio（FIR）has become a new temperature measurement method with the advantages of short response time,strong anti-interference ability,remote real-time and not affected by the environment.In particular,up-conversion rare earth luminescence thermometering nanomaterials have shown great application value in extreme and special temperature detection in toxic,confined environment,organisms and inside cells due to their excellent physical and chemical stability and luminescence properties.However,the existing up-conversion fluorescent temperature measuring materials are also faced with problems such as weak fluorescence intensity,low temperature sensitivity and small temperature measuring range.In this paper,rare earth niobate system with excellent physical properties,moderate phonon energy and high dielectric constant is selected as the matrix material,and the up-conversion luminescence and temperature sensing characteristics of Yb³⁺/Er³⁺and Yb³⁺/Tm³⁺co-doped systems are studied in order to improve the temperature sensitivity and temperature measurement range.The specific research work and results are as follows:1.The up-conversion luminescence and temperature sensing properties of LuNbO₄:Yb³⁺/Er³⁺nanocrystals were investigated.The modified molten salt method was used to prepare Yb³⁺/Er³⁺co-doped LuNbO₄ nanoparticles with uniform size and morphology.Taking ²H_11/2 and ⁴S_3/2 levels of Er³⁺ions as the thermal coupling energy levels,an up-conversion thermometer based on LuNbO₄:5mol%Yb³⁺and 1mol%Er³⁺nano-phosphor can be realized through fluorescence intensity ratio read-out method.The experimental results indicate LuNbO₄:5 mol%Yb³⁺,1 mol%Er³⁺nanoparticles have excellent optical thermometric sensitivity.The maximum absolute sensitivity and relative sensitivity is 0.0084 K^-1（at 673 K）and 11.34%K^-1（at 93 K）,respectively.The high absolute sensitivity may be attributed to the relative high phonon energy of LuNbO₄(-807 cm^-1),and the relative sensitivity increases with the energy level difference between thermally coupled levels.LuNbO₄:5 mol%Yb³⁺,1mol%Er³⁺nanoparticles exhibit excellent temperature measurement repeatability and the luminescence thermometry can be implemented in a wide temperature range of 93-673K.In addition,the opto-thermal properties of ²H_11/2 and ⁴F_9/2 uncoupled energy levels of Er³⁺ions were investigated.Based on the non-thermal coupling energy level,the absolute sensitivity reached a maximum of 0.0125 K^-1 at 673 K,while the relative sensitivity reached a maximum of 9.46%K^-1 at 93 K.In this work,a dual-mode temperature sensor based on fluorescence intensity ratio(²H_11/2/⁴S_11/2 and ²H_11/2/⁴F_9/2)was realized using a single luminescent center,which is an ideal candidate material for the development of nanothermometers.2.The particle size regulation and temperature sensing characteristics of LaNbO₄:Yb³⁺/Tm³⁺up-conversion nanocrystals were investigated.The modified molten salt method was used for successfully preparing Yb³⁺/Tm³⁺co-doped LaNbO₄nanoparticles.Controllable preparation of nanoparticles of different sizes was realized by updating the material synthesis process,which effectively enhanced the temperature measurement sensitivity of the nanoparticles.The measurement results demonstrate that as the size of LaNbO₄:Yb³⁺/Tm³⁺nanoparticles decrease from 140 nm to 100 nm,the sensitivity of the temperature sensor improve from 0.0204 to 0.024 K^-1.As the size of the nanocrystalline particles decrease,the proportion of surface active ions of the nanoparticle increases.The surface active ions of the nanoparticles seize a dominant position in the process of heat exchange with the environment,exhibit higher thermometric sensitivity.In addition,We continue to study the optically thermal properties of the ³F_2,3/¹G₄ and ³F_2,3/¹G_4（1）non-thermal coupling energy level of Tm³⁺at100 nm particle size.Absolute sensitivities based on the unthermally coupled energy levels ³F_2,3/¹G₄ and ³F_2,3/¹G_4（1）can reach maximum values of 0.0101 K^-1 and 0.0043K^-1 at 673 K,respectively.Therefore,Yb³⁺/Tm³⁺co-doped LaNbO₄nanoparticles are potential candidate materials for temperature measurement.