Understanding the electronic properties of BaTiO3 and Er3+ doped BaTiO3 films through confocal scanning microscopy and XPS: the role of oxygen vacancies.

Photonic and electronic properties exist inherently in ferroelectric barium titanate (BaTiO3); severe luminescence quenching also exists due to the insufficient confinement of excitons. In this sense, high optical emission can only be achieved by its chemical and structural modification. Thin BaTiO3 and Er:BaTiO3 films were grown by the spin coating method on a glass substrate at room temperature. Self-trapping of excitons in the thin BaTiO3 film and its structural modification due to the doping with Er3+ ions (Er:BaTiO3) are verified using scanning confocal fluorescence microscopy (SCFM), where self-trapping excitons never occured in its pure state. By thermal treatment and doping (BaTiO3 and Er:BaTiO3) we obtained localization of the excitons, which would further induce lattice strain around the surface defects, to accommodate the self-trapped excitons. With such a self-trapped state, the structure of BaTiO3 generates broadband emission of several overlapping bands between 1.95 and 2.65 eV at room temperature, while the structure Er:BaTiO3 showed defined emission bands at 2.24 and 2.35 eV, with very weak contributions of the emission due to the self-trapping state. The influence of the variation of the excitation wavelength using 1PE and 2PE on the emission bands of BaTiO3 and Er:BaTiO3 is also investigated. The results of enhanced emission bands suggest a clear dependence of the emission intensity on the excitation energy, where a ∼3 fold enhancement in emission has been demonstrated under Er3+ (1.55 eV) excitation, which can be attributed to effective energy transfer between the Er3+ ions. As a result, it is concluded that the developed BaTiO3 and Er:BaTiO3 can pave the way for future photonic devices.

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.

Tailoring ultrabroadband near-infrared luminescence in Bi-doped germanosilicate glasses.

Bi-doped glasses and optical fibers are extensively studied since they present broadband optical amplification in the near-infrared region (NIR), in which the optical telecommunication industry greatly depends for the transmission of optical signals. There are many scientific challenges about the NIR luminescent emissions from Bi ions, such as understanding its origin and further improving the associated optical amplification capacity. In this work, Bi-doped germanosilicate glass compositions with ultrabroadband NIR luminescence were fabricated, in the range of 925-1630 nm, which covers O, E, S, C, and L-telecommunication bands. An in-depth analysis of the impact of modifying excitation wavelengths, Bi content, and GeO2/SiO2 concentration ratio in the glass matrix demonstrates the possibility of considerably manipulating the Bi NIR luminescence, in terms of tuning emission parameters such as bandwidth, up to ~ 490 nm, and luminescence intensity. Based on theoretical and experimental luminescence data retrieved from the fabricated glasses, we demonstrate that the origin of broadband luminescence under all the considered excitation wavelengths can be ascribed to optical transitions of Bi0 ions. Therefore, an energy level diagram for Bi0 is proposed. We anticipate that our findings can provide clarifications to the existing uncertainty in the origin of Bi NIR emission, which will be useful to fabricate efficient future optical fiber amplifiers.

The role of tungsten oxide in Er3+-doped bismuth-germanate glasses for optical amplification in L-band.

A series of novel Er3+-doped bismuth-germanate glasses containing different tungsten concentrations with a molar composition of 97.5[(75 - x)GeO2-25Bi2O3-(x)WO3]-2Sb2O3-0.5Er2O3 (x = 5, 10, 15, 20, and 25 mol%) were fabricated. Their thermal properties are measured by differential scanning calorimetry. A structural investigation by Raman spectroscopy suggested that changes occurred in the glass network by WO3 incorporation. By laser excitation at 980 nm, a strong emission from Er3+ ions at 1532 nm is observed, while the WO3 addition caused changes in the emission spectra. The emission cross-section spectra of Er3+ are calculated by both McCumber and Füchtbauer-Ladenburg theories and their comparison showed these theories yielded slightly different results, but in both cases, the calculations showed that a gain signal in L-band can be achieved when 30% of the Er3+ ions are at the excited state. This study proves that the Er3+-doped bismuth-germanate glasses are suitable for optical fiber amplifier applications operating at C- and L-band.

Demonstration of multiple quantum interference and Fano resonance realization in far-field from plasmonic nanostructure in Er3+-doped tellurite glass.

It is crucial to control the tuning and improve the emission of a quantum emitter at the nanoscale. We report multiple Fano resonances in metallic nanostructures on an Er3+-doped tellurite glass. Periodic nanoslits were fabricated with a focused gallium ion beam on a gold thin film deposited on the tellurite glass. Is proposed a coupling function with Fano line-shape form, and the asymmetric parameter q for each resonance wavelength in the 515 to 535 nm region was calculated. This asymmetric resonance effect is a consequence of the quantum interaction between the continuum state, generated in the nanostructure, and the Stark splits of the [Formula: see text]H[Formula: see text] state.

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.

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

This manuscript reports on the interaction between (2)F5/2→(2)F7/2 radiative transition from Yb(3+) 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 Yb(3+) 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 Yb(3+) 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 Yb(3+) 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 Yb(3+) ions. We have found samples of low-quality cavities and strong coupling between the nanoparticles and the Yb(3+) 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.

Temperature oscillations of magnetization observed in nanofluid ferromagnetic graphite.

We report on unusual magnetic properties observed for nanofluid room temperature ferromagnetic graphite (with an average particle size of [Formula: see text] nm). More precisely, the measured magnetization exhibits a low temperature anomaly (attributed to the manifestation of finite size effects below the quantum temperature [Formula: see text]) as well as pronounced temperature oscillations above T = 50 K (attributed to manifestation of the hard-sphere type of pair correlations between ferromagnetic particles in the nanofluid).