Thermo-induced Phase Transformation Of NaYF₄:Eu³⁺ Nanoparticles Based On Cathodoluminescence Technology

Temperature is a basic parameter that affects physical,chemical,and biological systems,and plays a vital role in determining the state of matter.For nanoparticles,temperature not only plays a crucial role in the formation and structural characteristics of the material during the synthesis process;but also seriously affects the structure and performance of the material in subsequent applications.Similarly,changes in the structure and properties of the material can also be used to determine the specific temperature.Therefore,in-depth study of the effect of temperature on nanomaterials has important scientific significance.With the advancement of science and technology,cathodoluminescence?CL?technology has also released new vitality.By combining with scanning electron microscope?SEM?or transmission electron microscope?TEM?,the surface morphology and structure of the sample can be obtained,and the spectral information can also be obtained,thereby obtaining more useful conclusions.In this paper,two aspects of work have been carried out:on the one hand,combined with the TEM and SEM-CL technology,the change of the structure of fluoride nanoparticles caused by heating treatment has been studied;on the other hand,the change of the luminescent properties of different nano materials doped with rare earth ions with temperature has been systematically studied to realize the optical temperature measurement.The main contents are as follows:1.NaYF₄:5.0 mol%Eu³⁺nanoparticles with appropriate and uniform particle size were synthesized by coprecipitation method.After heating at different temperatures,the morphology and structure information of single nanoparticles were observed by TEM,and the fluorescence spectrum of Eu³⁺ion,the structure probe doped in the nanoparticles,was observed by CL.The study found that the morphology of the NaYF₄:5.0 mol%Eu³⁺nanoparticles after heat treatment changed significantly,and there were many areas with different contrast between light and dark inside the crystal,and the lattice information including crystal surface spacing and included angle also changes greatly.Through the comparative analysis of TEM structure parameters and CL spectrum data,it is shown that the process of fluoride to oxide transformation occurs in NaYF₄:5.0 mol%Eu³⁺nanoparticles after heat treatment.In this part,TEM and CL technology are combined to realize the correspondence between the morphology and luminescent information of several or even single nanoparticles,which is not only helpful to judge the structure information efficiently and quickly,but also provides new ideas on the interactions of electrons with the sample.2.The influence of temperature on the luminescent properties of NaYF₄ and YBO₃ nanoparticles doped with Ce³⁺and Tb³⁺was studied.With the increase of temperature,the luminescent intensity of Ce³⁺decreases obviously,which is due to the thermal quenching of 5d-4f transition of Ce³⁺.The relative sensitivity of NaYF₄: 5.0 mol%Ce³⁺was 0.22%K^-1 by using the temperature sensitive characteristics of Ce³⁺emission.Different from Ce³⁺,the 4f-4f luminescence of Tb³⁺has no obvious change with temperature,so it can be used as a reference.At the same time,through the process of energy transfer from Ce³⁺to Tb³⁺,the double emission of Ce³⁺ion blue light and Tb³⁺ion green light excited by a single wavelength?253 nm ultraviolet light?is realized.Therefore,the fluorescence intensity ratio of Ce³⁺/Tb³⁺ can effectively improve the temperature sensing performance of the material,such as the sensitivity of NaYF₄:5.0 mol%Ce³⁺,2.0 mol%Tb³⁺to 0.47%K^-1.Considering that part of the reason for the low sensitivity is the low degree of luminescence quenching of Ce³⁺in fluoride,YBO₃ system with high phonon energy was used to study.It was found that the sensitivity of YBO₃:1.0 mol%Ce³⁺was increased to 0.70%K^-1 in the temperature range of 288-333 K.When the concentration of Tb³⁺is 1.0 mol%,the absolute sensitivity is 1.18%K^-1 and the relative sensitivity is 0.498%K^-1.This shows that the ratio fluorescence technology based on Ce³⁺-Tb³⁺ ion pair is expected to be applied in the field of temperature sensing.