Green light emission at room temperature was achieved from nonhydrogenated amorphous silicon–nitrogen (a-SiN) thin films. The films were deposited by cosputtering a silicon target covered with metallic erbium platelets in an Ar+N2 atmosphere. According to the deposition conditions, the nitrogen concentration [N] reached ∼40 at. % rendering an optical gap of approximately 3.5 eV while the Er concentration [Er] was estimated to be ∼10 at. % in the present films. The high [Er] associated to the optical band gap allows the direct excitation of Er3+ ions. This optical excitation is more efficient at low temperatures as a consequence of the reduction in nonradiative processes, and when exciting the samples with the 488.0 nm line of an Ar+ laser which is in resonance with the F47/2Er3+ energy level. In addition to light emission at ∼520 and ∼545 nm, transitions in the infrared energy region could be easily verified in as-deposited samples.

In this work, two sets of lead fluoroindogallate glasses were studied with the aim of using them as active media for laser devices at the mid infrared (∼2.8 μm) and visible (∼0.54 μm) regions. The infrared and upconverted emissions of Er3+ in single and Er3+:Yb3+ codoped samples were analyzed, and it was observed that the best set of samples for 2.8 μm emission was the single doped one, and that as the upconversion (anti-Stokes luminescence) increased as a function of Yb3+ concentration, the infrared emission decreased in the same manner. The results suggest that the codoping with Yb3+ favors only the upconversion processes which depopulate the I11/24 level, reducing the 2.8 μm emission intensity. On the other hand, the Yb3+ codoping will certainly increase the efficiency of an upconversion based device. Quantum efficiencies of infrared emissions and radiative lifetimes were calculated by using the Judd–Ofelt approximation. Er3+–Er3+ and Er3+–Yb3+ energy transfer efficiencies were calculated using the measured lifetimes of the levels involved in the energy transfer processes.

In this letter, we investigate the midinfrared photoluminescence of a series of diode-pumped Er3+-doped and Er3+, Yb3+-codoped low-silica content aluminosilicate glasses. Emission at 2.8 μm was observed in both single doped and codoped samples. The effect of Yb3+ codoping of the Er3+-doped samples was such that, for example, for a 2 wt % Er3+-doped, the photoluminescence yield at 2.8 μm was found to be roughly three times larger than that of the single 2 wt % Er3+-doped sample. This behavior was attributed to the efficient sensitization of Er3+ by Yb3+ in our oxide based host glasses. The results reported in this letter, together with the outstanding mechanical, chemical, and thermal properties of these glasses, suggest that rare-earth doped calcium aluminate glasses may become an attractive host for the development of solid state lasers operating in the midinfrared.

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The combination of DNA barcodes and geometric morphometrics is useful to discriminate taxonomically controversial species, providing more precise estimates of biodiversity. Therefore, our goal was to assess the genetic and morphometric diversity in Nematocharax, a controversial monotypic and sexually dimorphic genus of Neotropical fish, based on sequencing of cytochrome c oxidase subunit I (COI) and morphometric analyses in seven populations of N. venustus from coastal rivers in Brazil. The average pairwise intrapopulation divergence in COI ranged from 0 to 2.2%, while the average pairwise interpopulation divergence varied from 0 to 7.5%. The neighbour-joining (NJ) tree resulted in five genetic groups (bootstrap ≥ 97%), which correspond to the five clusters delimited by the BIN System, GMYC, and bPTP, indicating that there might be at least five species (or OTUs) within Nematocharax. Morphometric differences among these genetic lineages were also identified. Apparently, sexual selection, restricted dispersal, and geographic isolation might have acted synergistically to cause the evolutionary split of populations. These data challenge the current view that Nematocharax is a monotypic genus inasmuch as evolutionarily significant units or even distinguished species were identified. Therefore, we recommend that the highly impacted coastal basins in northeastern Brazil should be prioritized in conservation plans.

Temperature dependent photoluminescence from porous silicon nanostructures: Quantum confinement and oxide related transitions J. Appl. Phys. 110, 094309 (2011) Photoluminescence of deep defects involving transition metals in Si: New insights from highly enriched 28Si App. Phys. Rev. 2011, 15 (2011 Photoluminescence of deep defects involving transition metals in Si: New insights from highly enriched 28Si J. Appl. Phys. 110, 081301 (2011) Dielectric effects on the optical properties of single silicon nanocrystals J. Appl. Phys. 110, 074312 (2011) Photoluminescence origins of the porous silicon nanowire arrays J. Appl. Phys. 110, 073109 (2011) Additional information on J. Appl. Phys. The emission energy dependence of the photoluminescence ͑PL͒ decay rate at room temperature has been studied in Si nanoclusters ͑Si-ncl͒ embedded in Si oxide matrices obtained by thermal annealing of substoichiometric Si oxide layers Si y O 1−y , y=͑0.36, 0.39, 0.42͒, at various annealing temperatures ͑T a ͒ and gas atmospheres. Raman scattering measurements give evidence for the formation of amorphous Si-ncl at T a = 900°C and of crystalline Si-ncl for T a = 1000°C and 1100°C. For T a = 1100°C, the energy dispersion of the PL decay rate does not depend on sample fabrication conditions and follows previously reported behavior. For lower T a , the rate becomes dependent on fabrication conditions and less energy dispersive. The effects are attributed to exciton localization and decoherence leading to the suppression of quantum confinement and the enhancement of nonradiative recombination in disordered and amorphous Si-ncl.

Luminescence data for Eu '+ and Gd'+ in fluoroindate glasses are compared to those of a fluorozirconate glass. Emission is observed from Eu3+ sD, (.I= 0, 1,2 and 3) and Gd3+ 6P ,,r excited-state levels and the results put in evidence Eu-Eu and Gd-Eu energy transfer processes. Vibronic bands related to a 320 cm-' vibrational mode could be observed for Eu3+ luminescent transitions with AJ=O, 1 and 2 and also for the 6P,~2+8S7~2 transition of Gd 3+. Lanthanide ion site symmetry is closer to an inversion center in fluoroindate &sses than it is in fluoroxirconate.

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