José A. Jiménez

Photoluminescence via plasmon resonance energy transfer in silver nanocomposite glasses

This paper reports the first spectroscopic demonstration of photoluminescence (PL) owing to plasmon resonance energy transfer (PRET) from silver nanoparticles (NPs) to luminescent species in glass. Optical absorption and PL spectroscopy experiments performed on the melt-quenched silver-doped glass indicate the presence of single Ag+ ions, Ag+–Ag+ and Ag+–Ag0 pairs, and Ag NPs. After thermal processing of the material, nonradiative energy transfer from the Ag+–Ag0 luminescent centers to Ag NPs is observed by uniform suppression of band emission and the vanishing of the excitation band associated. Furthermore, evidence for PRET is observed after glass heat treatment by the appearance of a new excitation band near the surface plasmon resonance peak of Ag NPs at about 420 nm, when emission of silver pairs is monitored around 550 nm. In fact, excitation at 420 nm leads to a band emission centered around 530 nm indicating that the excitation of luminescent silver species indeed takes place via PRET. The lumines...

Study of the enhancement of the magnetic properties of Fe70Al30 in the order-disorder transition

The order-disorder transition produced by ball milling in the intermetallic Fe70Al30 has been systematically studied by x-ray diffraction, calorimetry, and Mossbauer experiments. These techniques show a monotonous transformation that ends after 6 h of milling. In the transition, the lattice parameter increase amounts to 0.7% and there is a large enhancement of the alloy’s magnetism.

Spectroscopic properties of CuO, SnO, and Dy2O3 co-doped phosphate glass: from luminescent material to plasmonic nanocomposite

Prospective applications of noble metal and rare-earth co-doped dielectrics in optical devices demand for a comprehensive understanding of the influence of material composition and processing on resulting properties. In this study, we report on the spectroscopic properties of a 50P2O5:50BaO glass matrix containing copper, tin, and dysprosium prepared by melting and subsequently subjected to heat treatment (HT). An achievement in terms of material preparation is that addition of stoichiometric amounts of CuO and SnO dopants along with the source of Dy3+ ions (Dy2O3) is shown effective for the precipitation of Cu nanoparticles (NPs) during HT. Optical absorption and photoluminescence (PL) spectroscopy including emission decay dynamics are employed in the characterization of the co-doped material as prepared, and as a function of HT. The basic structure of the phosphate host is assessed by 31P nuclear magnetic resonance spectroscopy. The optical data suggests the presence of both Cu2+ and Cu+ ions in the melt-quenched co-doped glass together with the Dy3+ ions. Thermal processing is indicated to result in the chemical reduction of ionic copper species via Sn2+ and ultimately produces the non-luminescent plasmonic Cu particles. The presence of such NPs is also observed to produce a quenching effect on Dy3+ PL, interpreted in terms of an ion-to-particle excitation energy transfer operating via interband transitions in the nanoscale metal. Thus, the glass may act as either a luminescent material or a plasmonic nanocomposite desirable for nonlinear optics dependent upon its thermal history.

Real-Time Monitoring of Plasmonic Evolution in Thick Ag:SiO2 Films: Nanocomposite Optical Tuning

An in situ optical microspectroscopy study of the surface plasmon resonance (SPR) evolution of Ag nanoparticles (NPs) embedded in thick SiO(2) films deposited on soda-lime glass has been conducted during thermal processing in air. The temperature and time dependences of the SPR were analyzed in the context of Mie extinction and crystal growth theories and were discussed along with consideration of oxidation processes and film/substrate physicochemical interactions. At relatively high temperatures, Ag NPs were indicated to grow first through a diffusion-based process and subsequently via Ostwald ripening. At lower temperatures, an initial decrease in Ag particle size was indicated due to oxidation, followed by NP diffusion-based growth. The growth and oxidation stages appeared temperature and time dependent, allowing for the tuning of material properties. The product of Ag NP oxidation was revealed by photoluminescence spectroscopy performed ex situ as single Ag(+) ions. The oxidative effect of the air atmosphere on Ag NPs was shown to be ultimately circumvented by the thick nanocomposite film. The phenomenon was explained on the basis of the displacement of the Ag/Ag(+) redox equilibrium toward Ag NP stability after ion migration toward the substrate being self-constrained. In addition, the current spectroscopic approach has been proposed for estimating the activation energy for silver diffusion in the SiO(2) matrix.

Enhanced 1.53 μm emission of Er3+ ions in phosphate glass via energy transfer from Cu+ ions

Optimizing the efficiency of Er3+ emission in the near-infrared telecommunication window in glass matrices is currently a subject of great interest in photonics research. In this work, Cu+ ions are shown to be successfully stabilized at a high concentration in Er-containing phosphate glass by a single-step melt-quench method, and demonstrated to transfer energy to Er3+ thereby enhancing the near-infrared emission about 15 times. The spectroscopic data indicate an energy conversion process where Cu+ ions first absorb photons broadly around 360 nm and subsequently transfer energy from the Stokes-shifted emitting states to resonant Er3+ absorption transitions in the visible. Consequently, the Er3+ electronic excited states decay and the 4I3/2 metastable state is populated, leading to the enhanced emission at 1.53 μm. Monovalent copper ions are thus recognized as sensitizers of Er3+ ions, suggesting the potential of Cu+ co-doping for applications in the telecommunications, solar cells, and solid-state lasing ...

In situ optical microspectroscopy approach for the study of metal transport in dielectrics via temperature- and time-dependent plasmonics: Ag nanoparticles in SiO2 films.

This study proposes in situ optical microspectroscopy as a means for the investigation of particle growth and metal transport in nanocomposite systems based on the temperature- and time-dependent optical response of the material. The technique has been successfully employed for the real-time monitoring of the growth of Ag nanoparticles (NPs) in SiO(2) films deposited on soda-lime glass during thermal processing in nitrogen atmosphere. By fitting the surface plasmon resonance (SPR) profiles with spectra calculated by Mie theory in the quasi-static regime, the time variation in effective Ag particle size was determined and subsequently analyzed in the context of crystal growth theory. The Ag NPs were indicated to grow first through a diffusion-based process and subsequently via Ostwald ripening. The experimental determination of the activation energies associated with each one of the particle growth mechanisms was carried out based on the time evolution of the SPR of Ag NPs. Arrhenius-type analyses of a set of time-dependent isotherms allowed for estimating the activation energies at 2.3 eV for the diffusion-based growth and 2.8 eV for the ripening stage.

Origin of light emission and enhanced Eu3+ photoluminescence in tin-containing glass

Abstract A barium-phosphate glass matrix was co-doped with SnO and Eu 2 O 3 for investigating on material luminescent properties. Optical absorption and X-ray photoelectron spectroscopy (XPS) were employed in the characterization of tin species. The prevalence of divalent tin was indicated by the XPS data in accord with a conspicuous absorption band detected around 285 nm ascribed to twofold-coordinated Sn centers (isoelectronic with Sn 2+ ). Photoluminescence (PL) excitation spectra obtained by monitoring Eu 3+ emission from the 5 D 0 state revealed a broad excitation band from about 250 to 340 nm, characteristic of donor/acceptor energy transfer. Under excitation of such at 290 nm, the co-doped material exhibited a bright whitish luminescence, and a four-fold enhanced Eu 3+ emission relative to a purely Eu-doped reference. Time-resolved PL spectra recorded under the excitation at 290 nm exposed a broad band characteristic of the twofold-coordinated Sn centers and emission bands of Eu 3+ ions, which appeared well separated in time in accord with their emission decay dynamics. The data suggested that light absorption took place at the Sn centers (donors) followed by energy transfer to Eu 3+ ions (acceptors) which resulted in populating the 5 D 0 emitting state. Energy transfer pathways likely resulting in the enhanced Eu 3+ photoluminescence and the consequential light emission were discussed.

UV Emission of Gd3+ in the Presence of Cu2+: Towards Luminescence Quenching through Quantum Cutting?

The first investigation into the ultraviolet (UV) photoluminescence of gadolinium(III) in the presence of copper(II) is reported. A melt-quenched barium phosphate glass was used as a model matrix. The optical spectroscopy assessment shows that with increasing CuO concentration the Cu(2+) absorption band grows steadily, whereas the UV emission from Gd(3+) ions is progressively quenched. The data, thus, suggests the existence of a Gd(3+) →Cu(2+) energy-transfer process ocurring through quantum cutting. A downconversion/cross-relaxation pathway proceeding through a virtual state in Gd(3+) is proposed. These findings suggest gadolinium(III) could potentially be used in the optical sensing of copper(II).

Absorption spectroscopy analysis of calcium‐phosphate glasses highly doped with monovalent copper

CaO-P2 O5 glasses with high concentrations of monovalent copper ions were prepared by a simple melt-quench method through CuO and SnO co-doping. Spectroscopic characterization was carried out by optical absorption with the aim of analyzing the effects of Cu(+) ions on the optical band-gap energies, which were estimated on the basis of indirect-allowed transitions. The copper(I) content is estimated in the CuO/SnO-containing glasses after the assessment of the concentration dependence of Cu(2+) absorption in the visible region for CuO singly doped glasses. An exponential dependence of the change in optical band gaps (relative to the host) with Cu(+) concentration is inferred up to about 10 mol %. However, the entire range is divided into two distinct linear regions that are characterized by different rates of change with respect to concentration: 1) below 5 mol %, where the linear dependence presents a relatively high magnitude of the slope; and 2) from 5-10 mol %, where a lower magnitude of the slope is manifested. With increasing concentration, the mean Cu(+) -Cu(+) interionic distance decreases, thereby decreasing the sensitivity of monovalent copper for light absorption. The decrease in optical band-gap energies is ultimately shown to follow a linear dependence with the interionic distance, suggesting the potential of the approach to gauge the concentration of monovalent copper straightforwardly in amorphous hosts.

Photoluminescence of Eu3+-doped glasses with Cu2+ impurities

Glasses activated with Eu(3+) ions are attractive as luminescent materials for various photonic applications. Co-doping with copper has been proposed for enhancing material optical properties, but the quenching effect of Cu(2+) impurities on Eu(3+) emission in glass remains largely unexplored. In this work, Eu2O3/CuO-containing barium-phosphate glasses have been prepared by the melt-quench method, and the Eu(3+) photoluminescence (PL) quenching resulting from Eu(3+)→Cu(2+) energy transfer was evaluated. Optical absorption spectroscopy showed that with the increase in CuO concentration the Cu(2+) absorption band resonant with Eu(3+) emission (e.g. (5)D0→(7)F2 transition around 615 nm) developed steadily. As a result, Eu(3+) PL was progressively quenched. Evaluation of the quenching constants as a function of temperature in the 298-673K range showed differences basically within experimental error, consistent with a resonant transfer and lack of phonon-assisted processes. Moreover, analysis of the Eu(3+) emission decay dynamics revealed a strong correlation between the decay rates and Cu(2+) impurity levels. Results imply that for practical applications the levels of Cu(2+) in Eu(3+)/Cu(+)-activated glasses should be reduced if not removed as these will significantly limit device efficiency.