Design Of Fluorinated Core-shell Nanoparticles With The Properties Of Multi-fluorescence Emission And Optical-temperature Sensing

Photon upconversion?UC?refers to an anti-Stokes process in which two or more low energy photons are sequentially or stepwise absorbed via real intermediate long-lived electronic states,resulting in an excitation of a higher electronic state,emitting a higher energy photon.Photon UC has been reported for many types of nanomaterials,such as lanthanide-doped nano-structures,transition metal-doped nanoparticles,defects-doped nano-structures,quantum nano-structures and so on.Lanthanide-doped UC nanoparticles?UCNPs?are a major thrust area of current research on UC in nanoparticles.In order to realize the multi-fluorescence emission with the dual-mode excitation and light-temperature sensing,the cubic NaYbF₄:Nd³⁺@NaYF₄:Yb³⁺;hexgonal NaYF₄:Er³⁺@NaYF₄:Yb³⁺;NaGdF₄:Yb³⁺,Tm³⁺@NaGdF₄:Er³⁺;NaGdF₄:Er³⁺@NaGdF₄:Yb³⁺,Tm³⁺and NaGdF₄:Yb³⁺,Tm³⁺@NaGdF₄:Er³⁺,Ho³⁺have been synthesized and the light temperature sensing,multi-fluorescence and dual-mode excitation spectrum of synthetic samples have been studied.The details are as follow:The first chapter,the characters of rare earth doped materials,the luminescence mechanism,the preparation methods of rare earth doped core-shell nano-materials and their main applications and development status quo are introduced in detail.The second chapter,the cubic NaYbF₄:Nd³⁺@NaYF₄:Yb³⁺have been synthesized.Phase,shape and size of the resulting core–shell NPs are studied by X-ray diffraction and high-resolution transmission electron microscopy.The tunable green-white-yellow multicolor emissions are realized by tuning the Yb³⁺concentration in NaYF₄:Yb³⁺active-shell.Based on the changeof the intensity ratio of 523 nm to 543 nm with temperature,a better behavior as a temperature sensor has been obtained with a maximum sensitivity of 0.0018 K^-11 at400 K.The resulting active-core/active-shell NPs show bifunctional property and have potential application in fluorescent and temperature nano-probes.In the third chapter,in order to improve the luminescence intensity and fluorenscence lifetime of fluoride nanomaterials,it is proposed to use the core-shell coating to achieve the fluorescence enhancement.In this chapter,the NaYF₄:Er³⁺@NaYF₄:Yb³⁺have been synthesized.Phase,shape and size of the resulting core–shell NPs are studied by X-ray diffraction and high-resolution transmission electron microscopy.Compared with the core-only NaYF₄:Er³⁺NPs,a maximum97.56-foldoverallenhancementintheemissionintensityofEr³⁺ionsinthe NaYF₄:Er³⁺@NaYF₄:Yb³⁺NPs is achieved under980 nm infrared excitation,and a maximum38.6-fold overall enhancement is achieved under 1545 nm infrared excitation.The luminescence enhancement effect and color output exhibits a strong dependence on the doping concentrations of Yb³⁺in the NaYF₄:Yb³⁺active-shell.By analyzing the decay lifetimes of the emission bands,the giant luminescence enhancement is due to the significant increase in the near-infrared absorption and efficient energy transfer from Yb³⁺primary-sensitizers toEr³⁺activators via Yb³⁺bridging sensitizers.The fourth chapter,the hexagonal NaGdF₄:Yb³⁺,Tm³⁺@NaGdF₄:Er³⁺;NaGdF₄:Er³⁺@NaGdF₄:Yb³⁺,Tm³⁺have been synthesized.Phase,shape and size of the resulting core–shell NPs are studied by X-ray diffraction and high-resolution transmission electron microscopy.Fluorescence spectra were measured at excitation of 980 nm and 1545 nm.The red-green ratio of the sample and the effective bandwidth of the emission peak were studied.In this study,the multi-fluorescence is achieved.By adjusting the excitation power,the sample spectrum can be adjusted.In fifth chapter,the hexagonalNaGdF₄:Yb³⁺,Tm³⁺@NaGdF₄:Er³⁺,Ho³⁺have been synthesized.Phase,shape and size of the resulting core–shell NPs are studied by X-ray diffraction and high-resolution transmission electron microscopy.Under the dual-mode excitation,the fluorescence intensity have been enhanced about 2200%.