Enjie He

Enhanced red upconversion luminescence by codoping Ce3+ in β-NaY(Gd0.4)F4:Yb3+/Ho3+ nanocrystals

In this work, hexagonal phase NaY(Gd0.4)F4:Yb3+/Ho3+ nanocrystals were obtained by solvothermal method. The upconversion emission tuning from green to red in NaY(Gd0.4)F4:Yb3+/Ho3+ nanocrystals was successfully achieved by replacing Y3+ ions in the nanocrystal structure with Ce3+ ions under 980 nm excitation. The red upconversion emission intensity was enhanced with Ce3+ concentration increasing. The output colors for the samples can be clearly observed in a confocal microscopy setup. It was found that two efficient cross-relaxation processes between Ho3+ and Ce3+ ions had been employed to enhance red emission and suppress green emission. The possible upconversion mechanisms and conversion efficiency between Ho3+ and Ce3+ ions were investigated in detail. In addition, the influence of the matrix and surface properties on the upconversion emission of the samples was also discussed. The red upconversion emission of Yb3+, Ho3+ and Gd3+ codoped nanocrystals in this work will have great potential applications in biological imaging, magnetic resonance imaging agents, and display and anti-counterfeiting applications.

Higher Order Fano Resonances and Electric Field Enhancements in Disk-Ring Plasmonic Nanostructures with Double Symmetry Breaking

Optical properties of disk-ring plasmonic nanostructures with double symmetry breaking are investigated theoretically. Tunable higher order Fano resonance is achieved, and it is sensitive to the degree of asymmetry of the nanoring, the offset and the dimension of the nanodisk. It is demonstrated that such higher order Fano resonances originate from the destructive interference between the bright mode of the displaced nanodisk and the dark mode of the asymmetric nanoring. By tunning the asymmetry degree of the nanoring, the offset, and the dimension of the nanodisk, certain higher order Fano resonances can be suppressed or enhanced. Double asymmetry breaking also allows the realization of the stronger electric field enhancement, resulting from the stronger interaction between the displaced nanodisk and the asymmetric nanoring.

Facile fabrication and upconversion luminescence enhancement of LaF3:Yb3+/Ln3+@SiO2 (Ln=Er, Tm) nanostructures decorated with Ag nanoparticles

A novel hybrid nanostructure, that is a Ag nanoparticle decorated LaF(3):Yb(3+)/Ln(3+)@SiO(2) nanosphere (Ln=Er, Tm), was constructed by a facile strategy, and characterized by XRD, TEM, FTIR, XPS and UV-vis-NIR absorption. Obvious spectral broadening and red-shift on the surface plasmon resonance were obtained by adjusting the size and configuration of Ag nanoparticles. Effective upconversion luminescence enhancements for Er(3+) and Tm(3+) containing samples were obtained. It is suggested that the luminescence enhancement results from both the excitation and emission processes, and the configuration of the studied hybrid nanostructure is an efficient system to enhance the luminescence emission of rare earth doped nanomaterials. It is believed that the enhancement from the hybrid nanostructure will find great potential in the development of photovoltaic solar cells.

Local‐field effect on the fluorescence relaxation of Tm3+:LaF3 nanocrystals immersed in liquid medium

Tm(3+):LaF(3) nanocrystals were synthesized with hydrothermal technique. Local-field effect on the radiative relaxation rate was studied in the system of Tm(3+):LaF(3) nanocrystals immersed in several liquid media. The fluorescence lifetime was measured. It was found that the fluorescence decay presented the characteristics of second-order exponential decay, for which the contribution from the ions inside the nanocrystal and ions at the interface of the nanocrystal were distinguished. Investigating the experimental results with proposed models, we found that the surface effect had to be eliminated. For rare earth doped LaF(3) nanocrystals, real-cavity model well explains the influence of surrounding medium on the fluorescence relaxation rate.

Fluorescence characteristics of Tm3+ in different local environments

Fluorescence from ions in both the crystal and glass phases was investigated by selective excitation of Tm3+ doped transparent oxyfluoride glass ceramics containing LaF3 nanocrystals. The spectroscopic properties of ions in different local environments were studied. It was found that the glass phase favored blue up-conversion of Tm3+ when a pulsed red light was applied. The most efficient up-conversion was obtained when the excited state absorption was resonant with the excitation.

Unique adjustable UC luminescence pattern and directional radiation of peculiar-shaped NaYF 4 : Yb 3+ /Er 3+ microcrystal particle

A new design of peculiar-shaped β-NaYF4: 20% Yb3+/2% Er3+ hexagonal microcrystal (PSβHM) is proposed and its upconversion (UC) luminescence with adjustable color pattern is studied with near infrared excitation. Flower-like green UC luminescence emission pattern from blooming to withering process and intensive directional red emission are achieved by simply adjusting the focal point position of the excitation light. The mechanism that determines the unique UC luminescence phenomena are investigated systematically. The function of the internal light reflection and waveguide effect with annular microcavity is explored based on the structure characteristic of the hexagonal microplate. The current work may have great significant and potential applications in the development of optoelectronic device, color display, directional light and laser emission of microsystem.

Surface Enhanced Fluorescence by Plasmonic Nanostructures

The optically generated collective electron density waves on metal-dielectric boundaries known as surface plasmons have been of great scientific interest since their discovery. Being electromagnetic waves on noble nanostructure’s surface, surface plasmons resonance can strongly enhance the electromagnetic field. These strong electromagnetic fields near the metal surfaces have been used in various applications like surface enhanced spectroscopy, plasmonic lithography, plasmonic trapping of particles and plsmonic catalysis etc. Resonant coupling of localized surface plasmons to fluorescent emitters can strongly modify the emitted intensity, the angular distribution and the polarization of the emitted radiation and even the speed of radiative decay, which is so-called surface/metal enhanced fluorescence (MEF/SEF). In this chapter, we illustrate current progress in design of metallic nanostructures for efficient fluorescence signal amplification that utilizes propagating and localized surface plasmons, and also some critical parameters in SEF, such as spacer, wavelength dependence effect are also discussed.