Research On Up-conversion Luminescence Control And Anti-counterfeiting Application Of Rare Earth Fluoride Micro-nano Materials

Rare-earth Up-conversion（UC）micro/nano materials are novel materials that can convert low-energy photons to high-energy photons.Due to their unique near-infrared to visible emission properties,they have promising applications in various fields such as three-dimensional displays,biological tissue imaging,fluorescent probes,anti-counterfeiting applications and fingerprint development.However,for different applications,the luminescence intensity and luminescence color of the materials need to be modulated in different ways by controlling the precursor species,material ratios,dopant ion species and excitation wavelength at the sample synthesis stage.The purpose of this thesis is to adjust the fluorescence color and pattern dynamic changes,using laser confocal combined with optical microscope in-situ fluorescence imaging to achieve real-time dynamic fluorescent color patterns.When the laser power is increased,the green luminescence pattern gradually moves from the position of the excitation end of the microtube to the other end along the tube length direction,and finally drowns out the red dumbbell luminescence pattern.It also reveals the intrinsic reason for the excitation power control of dynamic luminescence.Based on the in situ oxidation reaction to construct lattice-mismatched fluorescent heterojunction structures by focal inscription of substrates,a new idea for the local in situ oxidation mechanism of fluoride crystals is provided.The one-dimensional porous tube structure was also constructed by combining the Yb³⁺concentration and annealing method,and the sensitive response of luminescence color to excitation wavelength,excitation power and scanning speed of NaLu F₄:Yb³⁺/Er³⁺upconversion micro/nano rods（UCRs）was realized.In particular,they were applied to anti-counterfeiting technology to achieve multi-modal anti-counterfeiting visible to the naked eye.Our upconversion particles are more suitable for multi-modal anti-counterfeiting applications due to their convenient preparation procedure,enhanced security and simple reading method compared to the complex core-shell structures reported in the literature.This study promotes the development of rare earth doped UCRs for advanced anti-counterfeiting applications and provides experimental basis and theoretical guidance for rare earth fluorescent materials towards market applications.The specific study is divided into four parts as follows:The first part:Briefly introduce the research background of this article and the excellent properties,components and luminescence mechanism of rare earth materials;Summarizes the synthesis methods and characterization methods of rare earth luminescent materials in recent years;Highlights the research progress of rare earth luminescent micro-and nanomaterials in recent years and analyzes the remaining problems;Finally,the significance and research content of this thesis are presented.The second part:Firstly,a series of uniform size Na Yb F₄:Ho³⁺microcrystalline particles were prepared by modifying the preparation process with sodium citrate-assisted hydrothermal method,and control the morphology and size of the particles by adjusting the p H and the ratio of citrate ions to lanthanide ions(Cit^3-/Ln³⁺);Characterize the crystalline phase structure of the sample,and use a laser confocal spectroscopy system to analyze its fluorescence performance and fluorescent real color photos the luminescence properties and the intensity and color of the dynamic luminescence pattern were studied by varying the excitation power and irradiation time,and it was found that the green luminescence first appeared at the excitation end of the unique red dumbbell microtubule,then gradually moved to the other end with increasing excitation power and drowned the red dumbbell pattern,and the green luminescence pattern gradually became larger when the irradiation time was extended,exploring the mechanism behind the luminescence.The reaction of O₂ and UC particles by laser irradiation heating caused the formation of Na Yb F₄-Yb OF heterojunction structure;The mechanism of Na Yb F₄:Ho³⁺UC microcrystals forming Na Yb F₄-Yb OF heterojunction based on in situ oxidation is proposed,which provides new ideas for the synthesis of local in situ oxidation mechanism and nanoheterojunction of rare earth fluoride crystals.The third part:A series of NaLu F₄:Yb/Er UCRs with similar morphology and uniform size were prepared by oleic acid alcohol-assisted hydrothermal method,and the luminescence color and intensity of UCRs were controlled by regulating the Yb³⁺concentration;The luminescence color and spatial pattern properties of NaLu F₄:Yb³⁺/Er³⁺microrods were systematically investigated by laser spectroscopy;The multi-mode luminescence of NaLu F₄:Yb³⁺/Er³⁺microrods was navigated based on annealing temperature combined with Yb³⁺concentration The multi-mode luminescence of NaLu F₄:Yb³⁺/Er³⁺microbars was modulated based on the combination of annealing temperature and Yb³⁺concentration change;The mechanism of luminescence color response was explained by navigating the energy transfer channel by adjusting the phonon coupling effect between the matrix lattice and dopant ions on the basis of incident energy;Finally,anti-counterfeit security inks were prepared using these UCRs and their potential applications in the field of anti-counterfeiting were explored;The potential applications were investigated by varying the excitation power,excitation wavelength and The scanning speed of the reading laser makes the fluorescent patterns printed with security inks change color,thus forming multi-modal anti-counterfeiting,which provides an experimental basis and theoretical guidance for rare earth fluorescent materials towards market applications.The fourth part:summarizes the research content and innovative studies of this thesis,and provides an outlook on the application of rare earth fluoride upconversion fluorescent materials in anti-counterfeiting applications.