Enhancement in the Photoluminescence Properties of SiO2:Ge Embedded in a Polymeric Matrix

Polymer films of styrene butadiene copolymer (SBC) mixed with SiO2:Ge powder were successfully obtained by the drop casting method. The SBC concentration (in chloroform solution) was 10%w/v and the SiO2:Ge powder was mixed (mass ratio 80:20 respectively). The thicknesses of the films obtained were 50, 100, and 200 μm. In addition, polymer films of polytetrafluoroethylene (PTFE) preparation (60% dispersion in water), were obtained mixing 2 ml of PTFE and 0.05g of SiO2:Ge powder with a mass relation of 98% polymer and 2% SiO2:Ge. The photoluminescence emission spectra (PL) of SBC doped with SiO2:Ge resulted in similar characteristics to those for SiO2:Ge powders, although their intensity shows an increase 3.5 times approximately, compared with the pure powder. On the other hand, the PTFE films with SiO2:Ge present just one peak in the PL emission at 439 nm but their intensity increases 18 times respect to the powder. The photoluminescence excitation (PLE) spectra of the SiO2:Ge powders show the characteristic peaks at 248 nm (most intense) and at 366 nm. However, when the powder is embedded either in SBC or PTFE the peak at 366 nm shows an important increase which seems to indicate an energy transfer from the polymer to the SiO2:Ge

Structural and optical studies of Er3+-doped alkali/alkaline oxide containing zinc boro-aluminosilicate glasses for 1.5 um optical amplifier applications

In the present work, we report on the optical spectral properties of Er3+ -doped zinc boro-aluminosilicate glasses with an addition of 10 mol % alkali/alkaline modifier regarding the fabrication of new optical materials for optical amplifiers. A total of 10 glasses were prepared using melt−quenching technique with the compositions (40-x)B2O3 − 10- SiO2 − 10Al2O3 − 30ZnO − 10Li2O − xEr2O3 and (40-x)B2O3 − 10SiO2 − 10Al2O3 − 30ZnO – 10MgO − xEr2O3 (x = 0.1, 0.25, 0.5, 1.0, and 2.0 mol %). We confirm the amorphous-like structure for all the prepared glasses using X-ray diffraction (XRD). To study the functional groups of the glass composition after the melt−quenching process, Raman spectroscopy was used, and various structural units such as triangular and tetrahedral-borates (BO3 and BO4 ) have been identified. All the samples were characterized using optical absorption for UV, visible and NIR regions. Judd-Ofelt (JO) intensity parameters (Ωλ , λ = 2, 4 and 6) were calculated from the optical absorption spectra of two glasses LiEr 2.0 and MgEr 2.0 (doped with 2 mol % of Er3+). JO parameters for LiEr 2.0 and MgEr 2.0 glasses follow the trend as Ω6>Ω2>Ω4 . Using Judd–Ofelt intensity parameters, we obtained radiative probability A (S−1 ), branching ratios (β), radiative decay lifetimes τrad (μs) of emissions from excited Er+3 ions in LiEr 2.0 and MgEr 2.0 to all lower levels. Quantum efficiency (η) of 4 I13/2 and 4 S3/2 levels for LiEr 2.0 and MgEr 2.0 with and without 4D7/2 level was calculated using the radiative decay lifetimes τrad. (μs) and measured lifetimes τexp. (μs). We measured the visible photoluminescence under 377 nm excitation for both LiEr and MgEr glass series within the region 390–580 nm. Three bands were observed in the visible region at 407 nm, 530 nm, and 554 nm, as a result of 2H9/2 → 4 I15/2 , 2H11/2 → 4 I15/2 and 4 S3/2 → 4 I15/2 transitions, respectively. Decay lifetimes for emissions at 407 nm, 530 nm, and 554 nm were measured and they show single exponential behavior for all the LiEr and MgEr glass series. From the photoluminescence and radiative decay lifetimes (τrad), we calculated the full-width at half-maximum (FWHM), emission cross-section ( ) and bandwidth gain (FWHM ) parameters. Near-infrared photoluminescence under 980 nm excitation was measured for all the LiEr and MgEr glass series in the region 1420–1620 nm. NIR emissions show a broadband centered at ∼1530 nm due to the transition of Er3+: 4 I13/ 2 → 4 I15/2 . Decay lifetimes for NIR emission at ∼1530 nm were measured and they show a quite exponential nature for all the LiEr and MgEr glass series. From the NIR emission spectra and decay lifetimes, we calculated the full-width at half-maximum (FWHM), the emission cross-section ( ) and the bandwidth gain (FWHM ) for the NIR emission and it shows FWHM of 50–70 nm for prepared glasses, emission cross-section of (∼3.5) 10−20 cm2 , while bandwidth gain was (∼25) 10−26 cm3

Efectos de la adición de plata en películas delgadas superconductoras basadas en Tl

La propuesta de este trabajo de investigación consiste en buscar las condiciones experimentales (tiempo y temperatura de talinación) para la obtención de películas delgadas superconductoras depositadas sobre substratos de plata con fase Tl-2223 y Tl-1223 además de la transición entre estas fases en películas delgadas con y sin plata usando el horno de una zona. Una vez obtenidas estas condiciones se plantea experimentar con 4 cantidades distintas de plata (evaluando su desempeño en el tamaño de cristal, las características eléctricas y estructurales de las películas delgadas superconductoras que presenten la fase Tl-1223) para poder encontrar la cantidad optima de Ag

Ultraviolet to near infrared down-conversion in {CaF}2:Nd3mathplusmathplus/Yb3mathplusmathplus/Limathplusmathplus phosphors

Down conversion (DC) in rare-earth-doped optical materials is a process of great interest for the possibility of a substantial increase of the efficiency of silicon solar cells. Here we report the structural and photoluminescence properties of co-doped CaF2 phosphors obtained by hydrothermal synthesis. In particular, the DC photoluminescence characteristics for UV (353 nm) excitation of Nd3+/Yb3+ co-doped CaF2 phosphors are discussed, underlining the effects due to the co-doping with Li+. The photoluminescence emission is dominated by the nearinfrared (NIR) Yb3+ emission peaked at 975 nm, although the excitation spectrum corresponds to the characteristic peaks associated with Nd3+ excitation at both the UV and visible wavelength ranges. The Nd3+ to Yb3+ energy transfer mechanisms were determined from a detailed analysis of the excitation spectra characteristics of Nd3+ and Nd3+/Yb3+/Li + doped CaF2 phosphors. DC photoluminescence for UV excitation was confirmed by both the analysis of DC quantum yield efficiency and effective quantum yield measurements. In the first case, an efficiency up to 150% was found, while the effective quantum yield measurements, carried out for the UV (DC) and visible (downshift) excitation and NIR photoluminescence emission, give values of 81 +/- 10% and 37 +/- 5% for excitation with 353 nm and 577 nm light, respectively

Efecto de la adición de fluór en las propiedades superconductoras de la fase TlBa2Ca2Cu3Ox depositada sobre substratos policristalinos de plata

Se presentan resultados sobre la incorporación del fluór en la fase superconductora TlBa2Ca2Cu3Ox, obtenida como película crecida sobre substratos de plata. La incorporación del fluór se realizó por dos procesos: utilizando la difusión simultánea del talio y fluór en el horno de dos zonas y otro incorporando el fluór desde el depósito de la película precursora. Con el primer proceso las cantidades incorporadas de fluór inhibieron la formación de la fase. En el segundo caso, después de la difusión del talio se obtuvieron trazas de la fase objetivo