Rare-earth Nanoluminescent Materials Controlled By Different Excitation Sources And Its Optical Anti-counterfeiting And X-ray Imaging Applications

Trivalent lanthanide ions(Ln³⁺)are endowed with unique and fascinating luminescent properties,due to their abundant energy levels of 4f electron configurations.Inherit the native transition behaviour of the lanthanide ions,Ln³⁺doping nanomaterials have aroused great interest among a wide range of applications,including lighting and displays,optical fibers and amplifiers,scintillators and imaging,and so on.Rare-earth-based nanophosphors with multi-mode/multi-color emission or efficient nanoscintillators can be obtained by proper structural design and excitation source regulation.In this thesis,a series of multi-shell rare-earth nanophosphors have been designed and prepared to obtain multi-mode/multi-color emission,by reasonable shell design and regulating different excitation laser.Furthermore,a type of rare-earth nanoscintillators have been synthesized by doping Ln³⁺sensitization to enhance their X-ray excited luminescence（XEL）.The design of multi-layer core-shell structure and the introduction of special sensitizers facilitate multi-mode emission and XEL enhance.The research work of thesis is as follows:1.Dual-excitation and dual-mode emission rare earth nanophosphors and their optical anti-counterfeiting applicationsMulti-shell nanoparticle Na YF₄@Na Gd F₄:Yb/Tm@Na YF₄:Eu@Na Gd F₄:Ce@Na YF₄:Ce/Tm has been designed and synthesized by continuously epitaxial growth method,which achieveed dual-mode upconversion（UC）/downconversion（DC）emission under excitation at NIR/UV light by doping appropriate Ln³⁺as sensitizer and activators in different shell layer.Na YF₄nanocrystals were synthesized as the core,Gd³⁺is introduced in the second layer to realize the energy transfer process between shells by the interfacial energy transfer（IET）mechanism.Luminescent centers Tm³⁺and Eu³⁺were doped in different shells,respectively.The UC/DC emission was achieved under Yb³⁺sensitization by energy transfer upconversion（ETU）mechanism and energy migration（EM）mechanism under Ce³⁺.The structure of the nanomaterials was characterized by electron microscopy and X-ray powder diffraction to prove the effective preparation of the five-layer core-shell nanoparticles.Spectroscopic test results showed that the nanomaterial exhibit UC blue/red emission and DC blue/red emission simultaneously under near-infrared（980 nm）and ultraviolet（254 nm）laser excitation.Finally,it is applied to optical anti-counterfeiting applications,which shows its potential in multilevel optical anti-counterfeiting applications.2.Enhanced Radioluminescence of Na Lu F₄:Eu³⁺Nanoscintillators by Tb³⁺Sensitization for X-Ray ImagingX-ray excited luminescence（XEL）of scintillators is of significance for the imaging application in the fields of medical detection,information retrieval and scientific research.Lanthanide doped rare-earth nanophosphors show potential applications as next-generation scintillators due to their facile synthesis,high chemical stability and photostability,adjustable emission of XEL.Herein,a new XEL enhanced Na Lu F₄-based nanophosphor is synthesized through doping Tb³⁺to sensitize Eu³⁺emission,facilitating the as-prepared nanoscintillators for X-ray imaging on opaque sample and biological specimen.The Na Lu F₄:Gd/Tb/Eu with 5%Tb-doping shows the highest XEL intensity owing to the energy transfer process between Tb³⁺and Eu³⁺.The Na Lu F₄:Gd/Tb/Eu（10/5/15 mol%）nanoparticles exhibited excellent scintillation performance with light yield of 15313 photons Me V^-1and low detection limit of 84.1 n Gy_airs^-1.X-ray imaging test using Na Lu F₄:Gd/Tb/Eu（10/5/15 mol%）-based scintillation film exhibited a high spatial resolution of 8.7 lp mm^-1.Furthermore,such Na Lu F₄:Gd/Tb/Eu（10/5/15 mol%）-based scintillation film has been applied in X-ray imaging with high contrast for a spring sealed in capsule and a crab.This work demonstrated a new sensitization strategy to enhance XEL based on rare-earth fluoride nanomaterials,and presented high-resolution X-ray imaging meet the imaging requirements of industrial nondestructive testing,safety inspection.