Prof. Armando J. Neves Profile

Prof. Armando J. Neves

at Univ of Aveiro

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Publications (3)

Proceedings Article | 1 June 2015 Paper

Defect luminescence in oxides nanocrystals grown by laser assisted techniques

J. Rodrigues, M. R. Soares, N. Santos, T. Holz, N. Ben Sedrine, C. Nico, A. J. Fernandes, A. Neves, F. Costa, T. Monteiro

Proceedings Volume 9519, 951906 (2015) https://doi.org/10.1117/12.2178392

KEYWORDS: Oxides, Luminescence, Zinc oxide, Ions, Nanoparticles, Crystals, Nanocrystals, Zirconium dioxide, Lanthanides, Doping

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Wide band gap oxides, such as ZnO, SnO₂ and ZrO₂, are functional materials with a wide range of applications in several important technological areas such as those including lighting, transparent electronics, sensors, catalysis and biolabeling. Recently, doping and co-doping of oxides with lanthanides have attracted a strong interest for lighting purposes, especially among them nanophosphors for bioassays. Tailoring the crystalline materials physical properties for such applications often requires a well-controlled incorporation of dopants in the material lattice and a comprehensive understanding of their role in the oxides matrices. These undoped or intentionally doped oxides have band gap energies exceeding 3.3 eV at room temperature and are known to exhibit optically active centers that span from the ultraviolet to the near infrared region. Typically, by using photon energy excitation above the materials band gap, high quality undoped materials display narrow emission lines near the band edge due to free and bound-exciton recombination, as well as shallow donor-acceptor recombination pairs. Additionally, broad emission bands are often observed in these wide band gap hosts, hampering some of the desired physical properties for further applications. Recognizing and understanding the role of the dopant-related defects when deliberately introduced in the oxide hosts, as well as their influence on the samples luminescence properties, constitutes a matter of exploitation by the scientific community worldwide. In this work, we investigate the luminescence properties of undoped and lanthanide doped oxide materials grown by laser assisted techniques. Laser assisted flow deposition (LAFD) and pulse laser ablation in liquids (PLAL) were used for the growth of ZnO, SnO₂ and yttria stabilized ZrO₂ (YSZ) micro and nanocrystals with different morphologies, respectively. Regarding the YSZ host, trivalent lanthanide ions were optically activated by in-situ doping and co-doping. The influence of the defect energy states on the optical properties of the different undoped and doped metal oxide hosts is investigated under ultraviolet and infrared excitation by means of photoluminescence and photoluminescence excitation.

Proceedings Article | 8 March 2014 Paper

ZnO micro/nanocrystals grown by laser assisted flow deposition

J. Rodrigues, A. J. Fernandes, D. Mata, Tiago Holz, R. Carvalho, R. Fath Allah, T. Ben, D. Gonzalez, R. Silva, A. da Cunha, M. Correia, L. Alves, K. Lorenz, A. Neves, F. Costa, T. Monteiro

Proceedings Volume 8987, 89871F (2014) https://doi.org/10.1117/12.2039907

KEYWORDS: Zinc oxide, Silver, Crystals, Nanoparticles, Particles, Luminescence, Composites, Scanning electron microscopy, Raman spectroscopy, Photomicroscopy

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Laser assisted flow deposition (LAFD) is a very high yield method based on a vapor-solid mechanism, allowing the production of ZnO crystals in a very short time. The LAFD was used in the growth of different morphologies (nanoparticles, tetrapods and microrods) of ZnO micro/nanocrystals and their microstructural characterization confirms the excellent crystallinity of the wurtzite structure. The optical properties of the as-grown ZnO crystals investigated by low temperature photoluminescence (PL) evidence a well-structured near band edge emission (NBE) due to the recombination of free (FX), surface (SX) and donor bound (D⁰X) excitons. Among the most representative emission lines, the 3.31 eV transition was found to occur in the stacking faults-free microrods. The luminescence behavior observed in H passivated samples suggests a closer relationship between this optical center and the presence of surface states. Besides the unintentionally doped micro/nanocrystals, ZnO/Ag and ZnO/carbon nanotubes (CNT) hybrid structures were processed by LAFD. The former aims at the incorporation of silver as a p-type dopant and the latter envisaging photovoltaic applications. Silver-related spherical particles were found to be inhomogeneously distributed at the microrods surface, accumulating at the rods tips and promoting the ZnO nanorods re-nucleation. Despite the fact that energy dispersive X-ray measurements suggest that a fraction of the silver could be incorporated in the ZnO rods, no new related luminescence lines or bands were observed when compared with the as-grown samples. For the case of the ZnO/CNT composites two main approaches were adopted: i) a direct deposition of ZnO particles on the surface of vertically aligned multi-walled carbon nanotubes (VACNTs) forests without employing any additional catalyst and ii) new ZnO/CNT hybrids were developed as buckypaper nanocomposites. The use of the LAFD technique in the first approach preserves the CNTs structure and alignment and avoids the collapse of the VACNTs array, which is a major advantage of this method. On the other hand, LAFD grown ZnO nanoparticles and tetrapods were used to produce ZnO/CNT buckypaper nanocomposites. When compared with the as-grown samples the PL spectra of the composites structures behave differently. For the case of the ZnO/VACNTs no changes on the peak position and spectral shape were observed. Only an enhancement of the overall luminescence was found to occur. On contrary, for the buckypaper nanocomposites notable changes on the spectral shape and peak position were observed, likely due to distinct surface band bending effects for the ZnO nanoparticles and tetrapods embedded in the CNTs.

Proceedings Article | 18 March 2013 Paper

Prospects on laser processed wide band gap oxides optical materials

M. Soares, J. Rodrigues, N. Santos, C. Nico, R. Carvalho, A. J. Fernandes, M. Graça, L. Rino, A. Neves, F. Costa, T. Monteiro

Proceedings Volume 8626, 862607 (2013) https://doi.org/10.1117/12.2016508

KEYWORDS: Ions, Optical fibers, Oxides, Crystals, Zirconium dioxide, Raman spectroscopy, Luminescence, Lanthanides, Laser processing, Zinc oxide

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