The Research About The Influences Of Metal Films And Nanoparticles On The Luminescence Of The Rare Earth Ions Doped Liquid Crystals

In this work, we studied the metal nanostructures (different kinds of metal nanoparticles and Au films) on the luminescence of Er3+/Yb3+co-doped Y2Ti2O7films,5CB and EuEDTA (Eu(TTA)3) doped in liquid crystals, respectively. The tuning surface plasmon resonance (SPR) or localized surface plasmon resonance (LSPR) of metal nanstructures by liquid crystal were also investigated. The main content of our work can be shown as follows:1. The photoluminescence of Er3+/Yb3+co-doped Y2Ti2O7films in the upconversion emission bands and near infrared emission when silver/gold (Ag/Au) nanoparticles (NPs) were doped. With the precipitation of the Ag nanoprisms, more intense green (525nm,546nm), red (659nm) upconversion emission bands and strong enhanced near infrared (NIR) emission were observed and the enhanced factors were up to16.7,15.6,17.7and5.6folds, respectively. The energy transfer were discussed in detail. The EBT process extra ordinarily contributes to the red UC emission. It is different from the results that the intensity of red emission is weaker than that of green emissions in Er3+single-doped Y2Ti2O7film. The accordance between the localized surface plasmon resonance (LSPR) of NPs and the UC emission band significantly increased the luminescence intensity. The efficiencies of the radiative emissions were enhanced also due to the hydroxyl groups primarily absorbed around the NPs.2. The localized surface plasmon (LSPR) was sensitive to the size and shape of the nanostructures, as well as the local surrounding environment. Liquid crystals (LCs) have a large optical anisotropy due to their anisotropic shape and alignment. By applying the anisotropy LCs, we achieve feasible tuning the LSPR. The far-field and near-field properties of a spherical nematic LCs coated metal NPs have been investigated in an external field, basing on the quasistatic theory. The resonant wavelength is tunable by varying metallic material of core, anisotropy extent and thickness of LCs. In addition, we find the extent of anisotropy of LCs have more significant effect on the full width at half maximum (FWHM) for the LSPR peak than the thickness. The field enhancement is along the incident polarization near the outer surface of the shell. The direction of field is reverse in the inner surface comparing with the one if outer shell. In contrast to isotropy shell, the LSPR shows an obvious red shift and field enhancement near outer surface of the shell always is stronger. Compared wit LSPR of gold film immersed in the air and LCs, LSPR redshift from550nm to591nm. It is in accordance with the simulated results based on the quasistatic theory.3. The enhanced photoluminescence in Ag/Au nanoparticles doped5CB LCs were observed. In presence of Au nanospheres, the enhancement of422nm was obvious, and the enhancement factor gradually increases until it reaches a maximum and then decreases. The optimum luminescence is obtained by the adding60μL Au nanosphere. The solubility of Ag nanospheres in LCs was easier than the Au nanospheres. In addition, we turned to the case of a5CB fluorophore, treated as an oscillating dipole, interacting with a Ag nanosphere in the near field. The effect on the radiative and nonradiative decay rate were further investigated, basing on the improved Mie theory.4. We prepared the europium complex [EuEDTA] and [Eu(TTA)3]. We showed LCs materials with narrow band red photoluminescence by doping a nematic host matrix with europium(Ⅲ) complexes. In the presence of Ag nanoprism, the luminescence of Eu3+ions was highly enhanced. The enhancement factor is8.The fluorescence lifetime of Eu3+at615nm was also observed, which further demonstrated the influence of LSPR effect.In addition, the europium complexes doped nematic LCs samples was excited by334nm (the excitation wavelength of5CB), considering the luminescence of5CB. The energy absorbed by5CB molecular was transferred to the Eu3+ions. The Eu3+ions then were excited. Finally, Eu3+ions return to the ground state from those levels through radiating615nm red light. The blue light radiated by5CB molecular coupled with the red light from Eu3+ions. The samples appeared light pink light, corresponding to the CIE chromaticity coordinates (X=0.3823, Y=0.2332) of the emission.Our work shows that the enhanced luminescence of rare earth ions and LCs was demonstrated in presence of the different metal nanostructures. The enhancement strongly depended on the nanostructures and the concentrations of nanoparticles. The tunable LSPR shift of metal NPs was achieved feasibly by liquid crystal. These would give us a better understanding of metal enhanced fluorescence by the metal nanostructures.