V. A. G. Rivera

Localized surface plasmon resonance interaction with Er3+-doped tellurite glass

We show the annealing effect on silver and Erbium-doped tellurite glasses in the formation of nanoparticles (NPs) of silver, produced by the reduction of silver (Ag+ → Ag0), aiming to an fluorescence enhancement. The absorption spectra show typical Localized Surface Plasmon Resonance (LSPR) band of Ag0 NP in addition to the distinctive absorption peaks of Er3+ ions. Both observations demonstrate that the photoluminescence enhancement is due to the coupling of dipoles formed by NPs with the Er3+ 4I(13/2) → 4I(15/2) transition. This plasmon energy transfer to the Er3+ ions was observed in the fluorescence spectrum with a blue-shift of the peaks.

White light and multicolor emission tuning in triply doped Yb3+/Tm3+/Er3+ novel fluoro-phosphate transparent glass-ceramics

New Yb3+, Er3+ and Tm3+ doped fluoro-phosphate glasses belonging to the system NaPO3–YF3–BaF2–CaF2 and containing up to 10 wt% of rare-earth ion fluorides were prepared and characterized by differential scanning calorimetry, absorption spectroscopy and up-conversion emission spectroscopy under excitation with a 975 nm laser diode. Transparent and homogeneous glass-ceramics have been reproducibly obtained with a view to manage the red, green and blue emission bands and generate white light. X-ray diffraction as well as electron microscopy techniques have confirmed the formation of fluorite-type cubic nanocrystals at the beginning of the crystallization process while complex nanocrystalline phases are formed after a longer heat-treatment. The prepared glass-ceramics exhibit high optical transparency even after 170 h of thermal treatment. An improvement of up-conversion emission intensity – from 10 to 160 times larger – was measured in the glass-ceramics when compared to the parent glass, suggesting an important incorporation of the rare-earth ions into the crystalline phase(s). The involved mechanisms and lifetime were described in detail as a function of heat-treatment time. Finally, a large range of designable color rendering (from orange to turquoise through white) can be observed in these materials by controlling the laser excitation power and the crystallization rate.

Study of Er3+ fluorescence on tellurite glasses containing Ag nanoparticles

Optical characteristics of tellurite glasses containing silver nanoparticles (NPs) and the influence on the emission spectrum of Er3+ ions were studied. The transitions 4f 4f from erbium ions, mainly the 4I13/2 → 4I15/2 transition that involve upconversion energy process, have a strongly dependence with the chemical structure of the rare earth ion. In the present work, silver nanparticles (NPs) embedded in the host vitreous material, show a significant enhance (or quenching) on the erbium fluorescence due the long-range electromagnetic interaction between the plasmon surface energy of the Ag NPs (Localized Surface Plasmon Resonance -LSPR) and the Er3+ ions.

Influence of film thickness on the optical transmission through subwavelength single slits in metallic thin films

Silver and gold films with thicknesses in the range of 120-450 nm were evaporated onto glass substrates. A sequence of slits with widths varying between 70 and 270 nm was milled in the films using a focused gallium ion beam. We have undertaken high-resolution measurements of the optical transmission through the single slits with 488.0 nm (for Ag) and 632.8 nm (for Au) laser sources aligned to the optical axis of a microscope. Based on the present experimental results, it was possible to observe that (1) the slit transmission is notably affected by the film thickness, which presents a damped oscillatory behavior as the thickness is augmented, and (2) the transmission increases linearly with increasing slit width for a fixed film thickness.

Control of the radiative properties via photon-plasmon interaction in Er3+ -Tm3+ -codoped tellurite glasses in the near infrared region.

The novelty of this paper is that it reports on the tuning of the spectral properties of Er3+ -Tm3+ ions in tellurite glasses in the near-infrared region through the incorporation of silver or gold nanoparticles. These noble metal nanoparticles can improve the emission intensity and expand the bandwidth of the luminescence spectrum centered at 1535 nm, covering practically all the optical telecommunication bands (S, C + L and U), and extended up to 2010 nm wavelength under excitation by a 976 nm laser diode. Both effects are obtained by the combined emission of Er3+ and Tm3+ ions due to efficient energy transfer processes promoted by the presence of silver or gold nanoparticles for the (Er3+)4I(11/2)→(Tm3+)3H5, (Er3+)4I(13/2)→(Tm3+)3H4 and (Er3+)4I(13/2)→(Tm3+)3F4 transitions. The interactions between the electronic transitions of Er3+ and Tm3+ ions that provide a tunable emission are associated with the dynamic coupling mechanism described by the variations generated by the Hamiltonian H DC in either the oscillator strength or the local crystal field, i.e. the line shape changes in the near-infrared emission band. The Hamiltonian is expressed as eigenmodes associated with the density of the conduction electron generated by the different nanoparticles through its collective free oscillations at each resonance frequency of the nanoparticle and their geometric dependence. A complete description of photon-plasmon interactions of noble metal nanoparticles with the Er3+ and Tm3+ ions is provided.

Plasmon-photon conversion to near-infrared emission from Yb(3+): (Au/Ag-nanoparticles) in tungsten-tellurite glasses.

This manuscript reports on the interaction between 2F5/2→2F7/2 radiative transition from Yb3+ ions and localized surface plasmon resonance (from gold/silver nanoparticles) in a tungsten-tellurite glass. Such an interaction, similar to the down-conversion process, results in the Yb3+ emission in the near-infrared region via resonant and non-resonant energy transfers. We associated such effects with the dynamic coupling described by the variations generated by the Hamiltonian HDC in either the oscillator strength, or the local crystal field, i.e. the line shape changes in the emission band. Here, the Yb3+ ions emission is achieved through plasmon-photon coupling, observable as an enhancement or quenching in the luminescence spectra. Metallic nanoparticles have light-collecting capability in the visible spectrum and can accumulate almost all the photon energy on a nanoscale, which enable the excitation and emission of the Yb3+ ions in the near-infrared region. This plasmon-photon conversion was evaluated from the cavity’s quality factor (Q) and the coupling (g) between the nanoparticles and the Yb3+ ions. We have found samples of low-quality cavities and strong coupling between the nanoparticles and the Yb3+ ions. Our research can be extended towards the understanding of new plasmon-photon converters obtained from interactions between rare-earth ions and localized surface plasmon resonance.

Optical gain medium for plasmonic devices

Metallic nanostructures upon resonant excitation can enhance the local electric field, which could be increased, if these nanostructures are embedded in a gain medium. In this sense, we propose a gain medium as a candidate for the development of nanowaveguide amplifier based on Er3+-doped tellurite glass with embedded silver nanoparticles (NPs). Those glasses are characteristic for their amplifying response in the telecommunication window, and when we embedded metallic NPs modified the crystalline potential surrounding to the Er3+ ions, due to an electric coupling between NP (received/emitter) and Er3+ ion (emitter) enhancement luminescence intensity from the 4I13/2→4I15/2 transition radiative of the Er3+ ions. Besides, the presence these NPs changes the refraction index these glass modifying the complex parameter β(neff) increasing the polarizability of the samples f(Ɛd). Therefore, a gain medium – Er3+ ions (amplification function in the telecommunication band) with silver NPs (luminescence enhancement) – can increment the propagation length of light into nanowaveguide.

Focusing surface plasmons on Er3+ions with convex/concave plasmonic lenses

Plasmonic lenses consisting of convex/concave concentric rings with different periods were milled with a Focused Gallium Ion Beam on a gold thin film deposited onto an Er3+-doped tellurite glass. The plasmonic lenses were vertically illuminated with an Argon Ion laser (488 nm) highly focused by means of a 20x objective lens. The focusing mechanism of the plasmonic lenses is explained by using a simple coherent interference model of surface plasmon-polariton generation on the circular grating as a result of the incident field. Particularly, this beam focusing structure has a modulated groove depth (concave/convex). As a result, phase modulation can be accomplished by the groove depth profile, similarly to a nano-slit array with different thicknesses. This focusing allows a high confinement of SPPs which excited the Er3+ ions of the substrate. The luminescence spectrum of Er3+ ions was then measured in the far-field, where we could verify the excitation yield of the plasmonic lens on the Er3+ ions. We analyze the influence of physical and geometrical parameters on the emission spectra, such as the periodicity and depth profile of the rings. The variation of these parameters resulted in considerable changes of the luminescence spectra.

Manifestation of geometric resonance in current dependence of AC susceptibility for unshunted array of Nb–Alx–Nb Josephson junctions

Abstract A pronounced resonance-like structure has been observed in the current dependence of AC susceptibility for two-dimensional array of unshunted Nb–Al x –Nb Josephson junctions. Using a single-plaquette approximation, we were able to successfully fit our data assuming that resonance structure is related to the geometric (inductive) properties of the array.

Resonant near-infrared emission of Er3+ ions in plasmonic arrays of subwavelength square holes

Periodic nanostructure arrays consisting of square holes were fabricated with a Focused Gallium Ion Beam on a gold thin film deposited onto the surface of an Er3+-doped tellurite glass. The nominal dimensions of the square elements are approximately 300×300 nm2, separated by 1.0 μm, such that we have arrays of approximately 15×15, 10×10 and 5×5 μm2 dimensions. The metallic nanostructures were vertically illuminated with a diode laser at 405 nm. The Er3+ luminescence spectrum in the near-infrared was measured in the far-field via the micro-luminescence technique. The excitation and emission of the Er3+ ions were obtained through of the so-called extraordinary optical transmission of excitation and emission light, respectively, via those squares array. In this way, metallic nanostructures sustaining surface plasmons can excite and change the emission properties of the Er3+ ions. Additional contributions on the emission spectra were achieved due to the influence of the gold metal film, i.e., the resonant properties from the plasmonic nanostructures can strongly influence the spectroscopic features of the Er3+ ions. Therefore, we present a systematic quantum mechanical experiment that shows the quantum plasmonic properties of these nanostructure arrays on the erbium ions, with direct applications for understanding and exploiting of nanophotonic devices.