Study On Fluorescence Regulation Effect Of Rare Earth Fluoride Inside And Outside Environment

Rare-earth (RE) doped inorganic crystal is an important branch of luminescent material. Their unique luminescent properties such as narrow luminescence band widths, long excited state lifetimes, abundant emission bands, weak luminescence backgrounds are originated from their characteristic electron configurations. In recent years, more interest on the RE doped luminescent materials, especially for nanomaterials has been inspired due to their tremendous application potentials in biology, nano-optoelectronics, information science, and so on. However, the low luminescence efficiency of RE doped luminescent materials has largely limited the further development of their practical applications. Therefore, exploring different strategies to realize efficient luminescence regulation and enhancement has great importance to both fundamental and applied investigation. In current dissertation, the fluorescence regulation and the mechanism behind it are systematically investigated by adjusting the host property, codoping ions, introducing metal nanostructures (surface plasmons) for rare earth doped nano or mico systems. The reuslts indicate that the evolution of internal environment can be realized by adjusting the host and codoping ions, and the introduction of surface plasmons induces the evolutions of both internal and external environments. These evolutions give the changes of radiative/nonradiatvive transition rate and relative populations of excied states, and the enhancement of excitation efficiency, which induces the effective luminescence regulation.The main results are summarized as follows:(1) The luminescence enhancement effects that induced by the replacement of host cations are investigated in Yb3+and Ln3+(Ln=Er3+, Ho3+, Tm3+and Eu3+) codoped fluoride hosts. It is shown that the variations of luminescence intensities for hypersensitive transitions are mainly attributed to the modification of local symmetry around the luminescent centers, while the overlapping level of the electron clouds is responsible for the luminescence efficiency change of conventional transitions.(2) The transformation from mixed cubic and hexagonal phases to pure cubic phase is successfully realized in Na-Ln-F (Ln=Lu, Y) fluorides by codoping with Mn+ions. The remarkable luminescence enhancements for both upconversion and downconversion, and approximate pure red emission are obtained simultaneously. It indicates that the quasi-single-band red emission was induced by efficient two-step energy transfer between Er3+and Mn2+, and the higher luminescence intensity should be appreciated for the lower local symmetry induced by the codoping of hetero-valence Mn2+ions. The fluorescence regulation effect induced by Mn2+codoping proposes a novel technical protocol for the development of biological probe with high sensitivity and resolution.(3) The morphology evolution and upconverted luminescence regulation effect are studied in fluoride microcrystals by codoping with small radius Sc3+. It was found that the codoping strategy could reduce the phonon energy of the host material and enhance the energy transfer rate of Yb3+to Ln3+(Ln=Er3+, Ho3+, Tm3+and Eu3+). The observation of effective upconversion emission in Eu3+originated from the two-photon process suggests the great application potential of the studied microcrystals in photovoltaic field.(4) Breaking the limitation of conventional core-shell structure, a novel hybrid nanosystem, Ag nanoparticles decorated LaF3@SiO2nanostructure is constructed based on the hydrothermal technique. Considerable upconversion luminescence enhancement is obtained by adjusting the surface plasmon resonance bandwith on a large scale. Excitation and emission enhacnements both appear in the current system. The construction of this semi-opened, semi-enclosed hybrid nanostructure broadens the research idea of metal-enhanced luminescence of RE doped nanomaterial.(5) The mechanism of downconverted luminescence regulation that induced by the surface plasmon is discussed in the constructed hybrid system. The competition between the plasmon-mediated enhancement of the excitation field and luminescence optical field, and the plasmon-induced nonradiative energy transfer is quantified. The association between the field enhancement and the quenching is explored. The current exploration might open a new way for the construction of metal-regulated RE luminescence system and the development of related theory.