Study On Fluorescence Characteristics Of Lanthanide - Doped Fluoride Micro - Nanocrystals

Rare-earth (RE) ions have been widely applied to luminescent materials because of their unique luminescent properties that originated from 4f electron configuration, which include sharp luminescence band, long excited state lifetime, abundant emission bands, low luminescence backgrounds, etc. In recent years, researchers have successfully developed a variety of methods for materials preparation. RE ion-doped micro- and nano-materials have presented great potential applications in lighting, nanomaterial solar cell, three-dimensional display, solid-state laser, biological marker and imaging, which has stimulated much attention. In current dissertation, the low phonon energy fluoride micro- and nano-materials are selected as the research object, and line of fluorescence regulation is investigated by ion codoping technology. Meanwhile, fluorescence characteristics of single microcrystal particle are carefully detected with a confocal setup. The main work is summarized as follow:(1) In LiYF4/NaYF4 microcrystal system, the UC luminescence properties and its dependence on Yb3+ concentration were studied with LiYF4/NaYF4:Yb3+/Pr3+ microcrystals and single LiYF4:Yb3+/Ln3+ (Ln=Er, Ho, Tm, Ho/Tm) microcrystal under 980nm INR excitation. The bright UC emission intensity from Pr3+ was observed in LiYF4/NaYF4 microcrystals, the relative intensity and spectral color of single LiYF4:Yb3+/Ln3+(Ln=Er, Ho, Tm, Ho/Tm) particle were adjusted by increasing Yb3+ concentration. The population change of Ln3+ doped with concentration increase of Yb3+ results in the occurrence of cross relaxation (CR) and concentration quenching. It is also found that the presence of EDTA in the synthesization process can control the morphology of micropaticle, the organic ligands of EDTA on the surface of microparticles affect the property of luminescence emission by changing the nonradiative relaxation rate.(2) The UC luminescence properties of Yb3+/Ho3+ codoped NaYF4 nanocrystals and single NaYF4 microrod were systematically investigated under INR 980nm excitation. The time controlled experiments were carried out and the grow mechanism of the microrods were proposed. The UC emission tuning from green to red in NaYF4: Yb3+/Ho3+ nanocrystals was successfully achieved by codoping Ce3+, which were attributed to two efficient CR processes between the Ho3+ and Ce3+ ions, suggesting that Ce3+ is an effective sensitizer for extending their application. An unusual candy-like luminescence emission pattern were observed from single NaYF4 microparticle, which is due to different energy transfer process result from excitation power change.