Controlled Synthesis And Properties Of Bismuth-based Oxide Luminescent Nanomaterials

Lanthanide-doped luminescent nanomaterials have the characteristics of narrow emission band,long fluorescence lifetime,low biological toxicity,and adjustable luminescence color.These excellent properties make it have broad application prospects in the fields of solid-state lighting,information storage,displays,solid-state lasers,anti-counterfeiting,sensors,solar cells,and biological imaging.However,the luminescence performance of lanthanide-doped luminescent nanomaterials is highly dependent on the chemical composition,crystal structure and morphology of the host material.As an element close to the lanthanide ion radius,bismuth has the characteristics of good biocompatibility,high atomic number,low radiation characteristics,strong X-ray attenuation,and low price,which makes bismuth-based nanomaterials have broad application prospects in the fields of lanthanide doped luminescence and biomedicine.Among them,lanthanide-doped bismuth-based oxide luminescent nanomaterials are gradually attracting wide attention from scholars at home and abroad due to their remarkable physical and chemical stability and thermal stability,high quantum yield.Based on this,this thesis mainly focuses on the controllable synthesis and performance of bismuth-based oxide luminescent nanomaterials.The main research content and results of this thesis include the following aspects:(1)Bi2O3 nanospheres co-doped with Yb3+/Er3+upconverting ions pair have been successfully synthesized via a facile hydrothermal method followed by a heat treatment.The resulting Bi2O3:Yb3+,Er3+nanospheres show a monodisperse spherical morphology with narrow size distribution(?180 nm)and display intense upconversion luminescence under 980 nm laser excitation.It is found that the crystal structure,morphology and upconversion luminescence properties of nanospheres have a direct relationship with the doping concentration of Yb3+.The introduction of Li+can greatly improve the upconversion luminescence performance,and the optimal doping concentration of lithium ions is 10%mol.These Bi2O3:Yb3+,Er3+nanospheres can be prepared in large quantities and can be easily modified with a layer of biocompatible polyethyleneimine(PEI)molecules.The yielded nanospheres could not only maintain uniform size and morphological characteristics,but also show good water dispersibility and biocompatibility.Remarkably,these Bi2O3:Yb3+,Er3+upconversion nanophosphors could also act as an effective contrast agent for X-ray computed tomography(CT)imaging,which show higher contrast efficacy than commercial iodine-based contrast agent.The proposed facile synthetic route and inexpensive matrix materials pave the way for broad use of these Bi2O3:Yb3+,Er3+nanospheres as ideal dual-mode bioimaging probes in biomedical field.(2)Yolk-shell structured Bi2SiO5:Yb3+,Er3+upconversion nanophosphors have been successfully synthesized via a simple template-assisted route,in which the reaction of Yb3+/Er3+co-doped bismuth precursor nanospheres with the silica capping layer in situ is ingeniously designed and controlled.The phase transition and morphology evolution are investigated in detail by X-ray powder diffraction and high-resolution electron microscopy to propose the formation mechanism of the yolk-shell nanostructure.The yielded Bi2SiO5:Yb3+,Ln3+(Ln=Er,Ho,Tm)nanophosphors can emit bright green/red/purple upconversion luminescence under the excitation of a 980 nm laser diode.The potential of the Bi2SiO5:Yb3+,Er3+nanophosphors as an optical nanothermometer is also demonstrated.(3)Core-shell Bi2SiO5 nanosystem with uniform morphology and narrow size distribution has been successfully synthesized via a facile template-assisted route.With the introduction of Eu3+,detailed studies are performed to evaluate its promise as Eu3+-based phosphor host.The yielded Bi2SiO5:Eu3+nanospheres are proven to be pure tetragonal phase via X-ray diffraction and Rietveld refinement.Moreover,the phosphor particles consist of monodisperse spheres with an average diameter of approximately 285 nm by high-resolution electron microscopy.When excited by near-ultraviolet(NUV)light,the abnormally high-intensity emission at 703 nm arising from the 5Do?7F4 transition of Eu3+is observed.The temperature-dependent photoluminescence spectra show that the optimized Bi2SiO5:20%Eu3+have satisfactory thermal stability with 63.7%of emission intensity at 423 K relative to 303 K.The deep-red light-emitting diode(LED)device fabricated by coating NUV chip with the Bi2SiO5:20%Eu3+phosphors is demonstrated.The newly-developed Bi2SiO5:Eu3+nanophosphors display commendable photoluminescence properties,demonstrating their promise as deep-red phosphor candidates for use in phosphor-converted LEDs.Finally,this paper is summarized,and the future work is prospected.