Optical Temperature Sensing Properties Of Er³⁺,Yb³⁺ Co-doped NaYF₄ And NaGdF₄ Up-conversion Phosphors

With the progress of The Times,science technology develop rapidly,and in the development and progress of various scientific fields,the research of materials has always been an important part that cannot be ignored.Because rare earth ions have rich energy level structure and unique 4f electron configuration,they are widely used in medical rescue,biological imaging,white light LED,solid-state laser,optical communication,functional detection,temperature sensing and other fields.Er³⁺have excellent research value in the field of up-conversion luminescence because of their special energy level structure of two thermally coupled energy levels.And the fluorescence intensity ratio temperature sensing technology based on the thermal coupling energy level of rare earth ions has made it the most popular research trend in the field of temperature sensing technology due to its advantages of fast response and high sensitivity.In addition,compared with traditional phosphor matrix material,NaReF4 fluoride has the advantages of low phonon energy,obvious emission spectrum,high luminescence intensity,long fluorescence life and low biological toxicity.Therefore,in this work,Er³⁺,Yb³⁺co-doped NaYF₄ and NaGdF₄ fluoride fluorescent materials were successfully prepared by hydrothermal method using EDTA as a chelating agent,and the optical temperature sensing properties of these two optical materials were systematically studied.The structure and morphology of the samples were characterized by XRD and FE-SEM.The XRD pattern showed that the crystal structure of NaYF₄ phosphors change from?phase?face-centered cubic?to?phase?primitive hexagonal?with the increase of EDTA/Re³⁺.The crystal structure of NaGdF₄ phosphors is hexagonal.FE-SEM showed that the?-NaYF₄ samples are uniform spherical particles,the?-NaYF4 samples are regular hexagonal slices,and the NaGdF4 samples were elongated particles.And the particle size of all the samples decreased with the increase of EDTA dosage.The temperature dependent up conversion emission spectra of NaYF₄ phosphor excited by a 980 nm near-infrared laser were measured.Temperature sensing properties of samples were studied based on the fluorescence intensity ratio for two thermally coupled levels ²H_11/21/2 and ⁴S_3/2/2 of Er³⁺.The results show that the optical temperature sensing sensitivity increased gradually along with the EDTA/Re3+increasing,no matter the samples are?phase or?phase,this is due to with the increase of EDTA/Re³⁺,The increase of organic impurities in the synthesis process will lead to the increase of lattice defects in the final product,This will increase the disorder of the surrounding environment of Er³⁺,resulting in the increase of the transition intensity parameter of Er³⁺.The disorder of the surroundings of the Er³⁺increases,and the transition intensity parameters increase.And the sensitivity maximum of?phase samples is 4.19×10^-33 K^-1(at 486 K,EDTA/Re³⁺=3),the sensitivity maximum of?phase samples is 4.66×10^-3K^-1(at 550 K,EDTA/Re³⁺=8).However,the relative sensitivity of the sample does not change with the increase of EDTA dosage,the relative sensitivity of the sample is only related to the energy level gap of Er³⁺two thermally coupled energy levels.The relative sensitivities of the samples of the?phase and the?phase have the maximum values at the temperature of 303 K,which are 1.05%K^-11 and 1.20%K^-1,respectively.This paper also measured the temperature dependent up conversion emission spectra of NaGdF₄phosphor excited by 980 nm near-infrared laser,and studied the fluorescence intensity ratio and temperature sensing performance of NaGdF4.Observation and analysis showed that the change law of sensitivity and relative sensitivity of NaGdF₄ phosphors was basically consistent with that of NaYF₄ phosphors.The sensitivity increases with the increase of EDTA/Re³⁺.When EDTA/Re³⁺=4,the maximum sensitivity is4.60×10^-3K^-1.The relative sensitivity is almost unchanged,and the maximum value is about 1.17%K^-1?at 303 K?.The results of this paper show that fluorides system phosphors prepared by hydrothermal with EDTA as chelating agent have the advantages of simple operation,controllable particle size,regular morphology and good dispersion.In addition,it was found that with the increase of the amount of chelating agent EDTA,the temperature sensing sensitivity of Er³⁺,Yb³⁺co-doped fluoride system fluorescent materials has improved significantly.The results of this paper have important guidance and reference significance for the design and preparation of Er³⁺activated upconversion temperature sensing materials.