Preparation And Luminescent Mechanism Of Er³⁺/Tm³⁺ Doped Upconversion Nanomaterials

With the development of science and technology,more and more people are investing in the preparation of upconversion nano-luminescent materials and the study of their luminescent properties.The upconversion luminescent material has unique anti-Stokes shift luminescence,which has the emission spectrum bandwidth,large emission intensity,stable structure,strong penetrating power,no lethality to biological tissue cells,and weak spontaneous background fluorescence.Upconversion nano-luminescent materials are often used in many fields,such as display,biomedicine analytical detection technology,biological therapy,etc.In this thesis,Sc₄Zr₃O₁₂ and?-NaErF₄ were used as matrix materials,respectively.The rare earth tri-doped Sc₄Zr₃O₁₂,doped ?-NaErF₄ and ?-NaErF₄ and sulfur-nitrogen-doped CDs composites were prepared by hydrothermal method.The morphology,luminescence properties and energy transfer of materials have been studied in depth,with the following main results:?1?Scandium oxide,zirconium nitrate and rare earth oxides are used as raw materials,Sc₄Zr₃O₁₂ nano luminescent materials were obtained by calcination under certain hydrothermal conditions.The prepared nano materials show excellent crystallinity by XRD test.Under the excitation of 980nm laser,the rare earth doped Sc₄Zr₃O₁₂ nano luminescent material has blue and green up conversion emission very well,When the Tm³⁺:Er³⁺:Yb³⁺rare earth doping ratio is 1.5%:2%:10%,the light emission effect is the best.The relationship between the emission spectrum and power density of the sample is analyzed,and the energy transfer mechanism is explored.It was determined that the Sc₄Zr₃O₁₂:2%Er³⁺,10%Yb³⁺,1.5%Tm³⁺samples are a three-photon process,green light and the red light upconversion emission are two-photon process.Using two pairs of thermal coupling energy levels of Sc₄Zr₃O₁₂ nanomaterials which are ¹G_4?a?and ¹G_4?b?of thulium ion and ²H_11/2 and ⁴S_3/2 of erbium ion,the relationship between fluorescence intensity and sensitivity with temperature was studied.The sensitivity of Tm³⁺reached the maximum at 373k,which was 4.16×10^-3K^-1.The sensitivity of Er³⁺reached the maximum at 573K,which was 3.47×10^-3K^-1.At the same time,the stability test shows that the fluorescent temperature sensor material with high sensitivity and high stability has been successfully prepared in both high and low temperature regions.?2?Mn²⁺/Tm³⁺doped ?-NaErF₄ nano-luminescent materials were prepared by hydrothermal method with oleic acid as complexing agent.The XRD results show that the hexagonal nanoparticles with high crystallinity can be formed when Mn²⁺is doped at low concentration.When the ratio is 10%,the red green ratio increases from 0.7 of pure?-NaErF₄ to 3.9.The intensity of green light is basically unchanged,and the intensity of red light is increased by more than 6 times.On this basis,through a series of Tm³⁺doping,the red green ratio increases first and then decreases.It can be seen that,compared with pure?-NaErF₄,Mn²⁺/Tm³⁺co-doped?-NaErF₄ not only has higher luminous intensity,but also increases the red-green ratio,and the red light ratio is higher.This kind of nano material,which is similar to red light emission,has a greater application prospect in biological imaging and detection.?3?The precursor solution was obtained by dispersing citric acid and thiourea in a certain amount of acetone,and the carbon quantum dots co-doped with sulfur and nitrogen were obtained after hydrothermal treatment.The carbon quantum dots co-doped with sulfur and nitrogen were compounded with?-NaErF₄,by introducing the intermediate energy level,the luminescence of?-NaErF₄ can be enhanced.A series of Tm³⁺doping was performed on pure?-NaErF₄ to find out that when the Tm³⁺doping ratio is 2%,the luminous intensity is pure?-NaErF₄ 18.8 times.On this basis,the prepared carbon quantum dots and?-NaErF₄:2%Tm³⁺were compounded.With the increase of the ratio of carbon quantum dots,the luminous intensity also increased,When the carbon quantum dots are 800?L,the red light intensity is 29.3 times that of pure?-NaErF₄ and strong red up conversion luminescence is obtained.The whole sample shows nearly monochromatic red light emission,which has great application prospects in solar energy utilization,biological imaging,preparation of multifunctional nanomaterial probes and other fields.