Preparation And Application Of Rare-Earth Doped Upconversion Nanocrystals

Lanthanide-doped upconversion nanoparticles have attracted great research interest due to their promising applications.However,conventional upconversion nanoparticles generally suffer from severe quenching effects,resulting in extremely weak luminescence,which greatly hinders their practical applications.To date,several approaches have been used to boost the upconversion luminescence of these functional nanoparticles,including chemical methods,physical strategies,and the search for better luminescent matrix materials.In this thesis,the research results achieved focusing on cesium zirconium fluoride（Cs-Zr-F）upconversion luminescent host material are briefly summarized as follows:（1）A trigonal phase Cs₂ZrF₆ upconversion luminescent host material was synthesized through an improved high-temperature co-precipitation method.The morphology and size of Cs₂ZrF₆ nanocrystals were controlled by modulating the reaction temperature,reaction time,OA/ODE ratio and the amount of total substance.The results indicated that the best morphology was obtained at a total amount of 1 mmol,a reaction temperature of 280℃,and an OA/ODE ratio of 8:12 for 1 h.The cubic phase Cs₂ZrF₆:Yb/Ln（Ln=Er,Tm,Ho）nanocrystals showed typical upconversion spectra under 980 nm laser excitation using different rare earth ion pairs（Yb/Er,Yb/Tm,Yb/Ho）doping.（2）The upconversion luminescence properties of Cs₂ZrF₆:Yb/Er/Na nanocrystals were successfully improved by Na⁺doping.In particular,the corresponding TEM Fourier transform diffraction patterns of the nanocrystals,which show obvious lattice stripes,indicate that the Cs₂ZrF₆:Yb/Er/Na nanoparticles are well crystallized.The XRD results indicate that the Na⁺ions replace the Cs sites leading to matrix lattice shrinking.The Na⁺doping improves the crystallinity of the nanocrystals and reduces the local symmetry of the activator ions,and this synergistic effect enhances the upconversion emission intensity of Cs₂ZrF₆:Yb/Er nanocrystals by up to about 34 times.（3）The Li⁺doping was employed to improve the upconversion luminescence efficiency of Cs₂ZrF₆:Yb/Er nanocrystals,and it was observed that the upconversion luminescence efficiency of Cs₂ZrF₆:Yb/Er nanocrystals was significantly enhanced by a factor of 185 under the condition of composite of two or three different phases.The application of this new strategy opened a new approach for the enhanced luminescence efficiency of upconversion nanocrystals and laid the foundation for the application of rare earth-doped nanomaterials in emerging fields in the future.