14 research outputs found
Diez prácticas y una filosofía en la enseñanza de la física
No full textThis work presents a «philosophy» of teaching physics through the carrying out of ten laboratory demostrations during the last course at high school or the first years faculty level.That philosophy consists in the simultaneous development of experimental and theoretical teaching in the same lecture hall, using for that simple experimental demonstrations.The data garhered by severa! groups of students also allows an introduction to the statistical handling of measurements.The selection of the experiments is not unique and can be ajusted by the teacher according with the apparatus available in a particular Center, although those here presented are a wide and reasonable selection.Finally, the inclusion of introductory biographic notes provides a connection with the historic and human aspects of the development of science.Este trabajo presenta una cierta «filosofía» de la enseñanza de la física a través de la realización de diez prácticas de laboratorio a nivel de C.O.U. y primer curso de Facultad de Ciencias.La mencionada «filosofía» consiste en que los alumnos deben acompañar y simultanear la realización de experiencias sencillas de forma conjunta, en la misma clase y en paralelo con la teoría.Los datos obtenidos por diversos grupos de alumnos sobre la misma experiencia son discutidos globalmente proporcionando una buena estadística.La selección de prácticas no es única ni mucho menos, sino que puede ser variada a voluntad del docente de acuerdo con sus posibilidades experimentales, aunque las aquí presentadas ofrecen una selección amplia y asequible.Finalmente se han incluido también algunas notas biográficas para conectar al estudiante con aspectos humanos e históricos del desarrollo de la Ciencia
Time resolved confocal luminescence investigations on Reverse Proton Exchange Nd:LiNbO3 channel waveguides
No full textIn this work we report on the time and spatial resolved fluorescence of Neodymium ions in LiNbO3 channel waveguides fabricated by Reverse Proton Exchange. The analysis of the fluorescence decay curves obtained with a sub-micrometric resolution has evidenced the presence of a relevant fluorescence quenching inside the channel waveguide. From the
comparison between diffusion simulations and the spatial dependence of the 4F3/2 fluorescence decay rate we have concluded that the observed
fluorescence quenching can be unequivocally related to the presence of H+ ions in the LiNbO3 lattice. Nevertheless, it turns out that Reverse Proton Exchange guarantees a fluorescence quenching level significantly lower than in similar configurations based on Proton Exchange waveguides. This fluorescence quenching has been found to be accompanied by a relevant red-shift of the 4F3/2 -> 4I9/2 fluorescence ban
Media 1: Temporal dynamics of IR-to-visible up-conversion in LiNbO<sub>3</sub>:Er<sup>3+</sup>/Yb<sup>3+</sup>: a path to phosphors with tunable chromaticity
No full textOriginally published in Optical Materials Express on 01 November 2012 (ome-2-11-1529
Continuous wave waveguide laser at room temperature in Nd3+-doped Zn:LiNbO3
No full textCopyright (2001) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Applied Physics Letters 79.25 (2001):4088-4090 and may be found at http://apl.aip.org
Fabrication of photorefractive damage-resistant active waveguides based on Zn-indiffused LiNbO 3
No full textProton exchange, anneal proton exchange, and reverse proton exchange waveguides in Er:LiNbO 3
No full text
Structural, photoluminescent properties and Judd-Ofelt analysis of Eu3+-activated CaF2 nanocubes
No full textEu3+-doped CaF2 nanocubes with variable europium concentration, [Eu3+] = 0, 0.6, 1.3, 1.7, 2.2 and 5.4 mol%, have been synthesized by a direct precipitation route. It has been found that, within this concentration range, the nanoparticles present the fluoride-type crystalline structure and the characteristic cubic shape of CaF2 crystals. The nanoparticle size follows a log-normal distribution with a mean value decreasing with the Eu3+ content. Rietveld refinement has been performed to calculate the lattice parameter and crystallite size. Eu3+ concentration affects both parameters giving rise to an increase in the lattice parameter and a reduction of crystallite size. The luminescent properties of Eu3+ ions in these nanostructures have been investigated under CW and pulsed excitation. A Judd-Ofelt analysis, as function of the Eu3+ content, has been performed to determine the transition probabilities, radiative lifetimes and branching ratios of the 5D0 emitting level. It was found that and Judd-Ofelt intensity parameters are dependent on the doping level, showing an evolution that indicates a decrease in the Eu3+ site local symmetry with increasing Eu3+ concentration. Finally, it has been observed that the characteristic luminescence decay time of the 5D0 manifold is reduced with increasing Eu3+ concentration. This effect is partially due to an increase of radiative transition probability, associated with a reduction in the local symmetry of the lanthanide ions, and also to the occurrence of concentration quenching effectsThis work has been partially supported by Ministerio de Economía
y Competitividad and Ministerio de Ciencia, Innovación y
Universidades under projects MAT2016-75716-2-2-R and RTI2018-
101020-B-I00
Crystal Structures and Photoluminescence across the La<sub>2</sub>Si<sub>2</sub>O<sub>7</sub>–Ho<sub>2</sub>Si<sub>2</sub>O<sub>7</sub> System
No full textIt is well-known that when an RE2Si2O7 matrix is doped with active lanthanide
ions, it displays promising luminescent responses for optical applications.
The crystalline structure adopted by the silicate matrix as well as
the distribution of the dopants among the available RE crystallographic
sites have important effects on the luminescent yields of these compounds.
The present study is aimed at analyzing the structural behavior as
well as the luminescent properties of Ho3+-substituted
La2Si2O7. Several compositions across
the La2Si2O7–Ho2Si2O7 system were synthesized using the sol–gel
method followed by calcination at 1600 °C. The resulting powders
were analyzed by means of X-ray and neutron diffraction to determine
the phase stabilities across the system. The results indicated a solid
solubility region of G-(La,Ho)2Si2O7 which extends to the La0.6Ho1.4Si2O7 composition. Compositions richer in Ho3+ show a two-phase domain (G+δ), while δ-(La,Ho)2Si2O7 is the stable phase for Ho3+ contents higher than 90% (La0.2Ho1.8Si2O7). Anomalous diffraction data interestingly indicated
that the La3+ for Ho3+ substitution mechanism
in the G-(La,Ho)2Si2O7 polymorph
is not homogeneous, but a preferential occupation of Ho3+ for the RE2 site is observed. The Ho3+-doped G-La2Si2O7 phosphors exhibited a strong green
luminescence after excitation at 446 nm. Lifetime measurements indicated
that the optimum phosphor was that with a Ho3+ content
of 10%
