Zn 1−x Mn x O nanostructures were synthesized via the microwave-assisted hydrothermal method, which rapidly produces particles of controlled size and morphology. Samples were analyzed considering the effects of manganese ion concentration. XRD revealed that all samples had wurtzite-type structure with Mn 2+ ions incorporated in the oxide lattice. UV−vis spectra showed absorption bands from the d−d transitions of Mn 2+ ions. As the doping concentration increased, the value of the energy gap decreased, indicating intermediary energy levels within the band gap in the Mn-doped ZnO samples. All samples produced broadband photoluminescence (PL) emissions in the yellow−orange− red range. Additionally, the PL intensity decreased with Mn 2+ ion incorporation into the ZnO lattice due to the creation of new recombination centers. Microscopy images showed that manganese in the ZnO matrix produced homogeneously distributed nanostructures. EPR results indicated two locations of Mn 2+ ions in the ZnO lattice, lower concentrations in the core of the lattice and higher concentrations at the surface.

Abstract-New technologies for ultra-dense WDM-PON (udWDM-PON), enabled by coherent techniques and low cost devices, are developed for an efficient utilization of the optical spectrum, revealing that the "Wavelength-to-the-User" concept can be feasible. In this work, an udWDM-PON with only 6.25 GHz channel spacing is implemented with conventional DFB lasers, for a splitter-based PON infrastructure with 256 ONUs. The results of the analysis of udWDM access network architecture with respect to their associated complexity, cost and migration scenarios, exhibit the potential for higher aggregate throughput, higher split ratios and node consolidation, when compared to competing technologies.Index Terms-Fiber optical communications, fiber-to-thehome, access networks, PON, WDM.

No abstract

Semimagnetic Bi2–x Mn x S3 nanocrystals (NCs) with a mean size of approximately 4.0 nm were successfully synthesized by fusion in a host glass and investigated by several experimental techniques. Transmission electron microscopy and atomic force microscopy/magnetic force microscopy images confirmed the growth of the Bi2–x Mn x S3 NC samples, showing uniform distribution of the total magnetic moment in the nanocrystals. X-ray diffraction measurements revealed that the as-produced nanocrystals are single-phase, nanosized, and crystallized in the orthorrombic structure and that Mn2+-ions had replaced Bi3+-ions. Electron paramagnetic resonance (EPR) spectra of the doped samples showed six hyperfine lines associated with the S = 5/2 spin half-filled d-state and characteristic of Mn2+ ions. EPR spectra simulated compared fairly well with experimental results and indicated the incorporation of Mn2+ ions in the core and surface in Bi2–x Mn x S3 NCs.

Iron-doped bismuth sulphide (Bi2−xFexS3) nanocrystals have been successfully synthesized in a glass matrix using the fusion method. Transmission electron microscopy images and energy dispersive spectroscopy data clearly show that nanocrystals are formed with an average diameter of 7–9 nm, depending on the thermic treatment time, and contain Fe in their chemical composition. Magnetic force microscopy measurements show magnetic phase contrast patterns, providing further evidence of Fe incorporation in the nanocrystal structure. The electron paramagnetic resonance spectra displayed Fe3+ typical characteristics, with spin of 5/2 in the 3d5 electronic state, thereby confirming the expected trivalent state of Fe ions in the Bi2S3 host structure. Results from the spin polarized density functional theory simulations, for the bulk Fe-doped Bi2S3 counterpart, corroborate the experimental fact that the volume of the unit cell decreases with Fe substitutionally doping at Bi1 and Bi2 sites. The Bader charge analysis indicated a pseudo valency charge of 1.322|e| on FeBi1 and 1.306|e| on FeBi2 ions, and a spin contribution for the magnetic moment of 5.0 µB per unit cell containing one Fe atom. Electronic band structures showed that the (indirect) band gap changes from 1.17 eV for Bi2S3 bulk to 0.71 eV (0.74 eV) for Bi2S3:FeBi1 (Bi2S3:FeBi2). These results are compatible with the 3d5 high-spin state of Fe3+, and are in agreement with the experimental results, within the density functional theory accuracy.