Water Molecules Probes Based On Upconversion Nanoparticles

Water molecule sensing is of great significance in the fields of biomedicine,precision agriculture,chemical industry,and food inspection.In recent years,optical water molecule probes have attracted much attention due to the advantages of easy preparation,fast response,and high stability.As one of optical water molecule probes,rare-earth-ion-doped upconversion nanoparticles have aroused great research interest because of the advantages of high photostability,fast response speed,small volume,and free of autofluorescence background.However,water molecule probes based on upconversion nanoparticles still have the disadvantages of low sensitivity and lack of a clear understanding of the sensing mechanism.In the thesis,I selected Tm³⁺ions as the luminescent ions of upconversion nanoparticles,and studied their characteristics and mechanisms for water molecule sensing.The main contents are as follows:（1）I theoretically optimized the upconversion luminescence characteristics of nanoparticles with Tm³⁺ions as luminescent centers.The influences of the physical properties of sensitizer Yb³⁺ions and activator Tm³⁺ions,energy transfer efficiency between sensitizer Yb³⁺ions and activator Tm³⁺ions,and morphological geometry of the Na Gd F₄:Yb³⁺/Tm³⁺nanoparticle on the luminescence efficiency were studied.（2）I numerically simulated a water molecule probe based on a single NaGdF₄:Yb³⁺/Tm³⁺upconversion microrod.In order to improve the sensitivity of water molecule probes based on upconversion nanoparticles,I chose Tm³⁺ions as the luminescent centers,and employed a whispering gallery mode resonator.Compared with traditional water molecule probes based on upconversion nanoparticles,the sensitivity of the water molecule probe based on the whispering gallery mode resonator was improved by about an order of magnitude in theory.Moreover,the influences of the indicator wavelength,doping concentration of sensitizer Yb³⁺ions and activator Tm³⁺ions,quality-factor of the microcavity,and pump power on the detection sensitivity were studied.（3）I experimentally studied NaLuF₄:Yb³⁺/Tm³⁺/Gd³⁺upconversion nanoparticles for water molecule probing.First,I prepared the Na Lu F₄:Yb³⁺/Tm³⁺/Gd³⁺upconversion nanoparticles based on the solvothermal method,and studied the influences of the indicator wavelength,doping concentration of sensitizer ions and activator ions on the sensitivity.Then,I demonstrated the sensitivity of water molecule probing in anhydrous ethanol as 6.141%/vol%.Finally,I developed the upconversion-nanoparticle-coated micro-fiber water molecule probe,for the sensing of water molecules.