Luís Carlos | Universidade de Aveiro (original) (raw)
Papers by Luís Carlos
Multifunctional materials working under solely visible-light are expected to play a significant r... more Multifunctional materials working under solely visible-light are expected to play a significant role in photo-electronics, in particular photo-switches, photo-optical sensors, smart windows, displays, optical storage memories, and self-cleaning materials.<div>In this work, we have modified the surface of a versatile semiconductor material (TiO<sub>2</sub>) with a noble metal (copper), and simultaneously doped its lattice with a rare-earth element (neodymium). Exploiting the ability of a semiconductor to generate an exciton upon excitation, a multifunctional material working with visible-light and showing photochromic, photoluminescent and photocatalytic activity was engineered. Advanced transmission electron microscopy techniques – aberration-corrected imaging combined with image simulation, statistical analyses and electron energy-loss spectroscopy – were used to characterise thoroughly the structure and local chemical environment as a function of the Nd<sup>...
Materials Science Forum, 2006
The main information transmission limitation in optical communications employing SiO 2 optical fi... more The main information transmission limitation in optical communications employing SiO 2 optical fibres is imposed by the optical pulses temporal broadening, resulting from the dispersive properties of the transmission medium (chromatic dispersion). Usually, this dispersion is modelled assuming a-0.4 meV/ºC dependence of the 11 eV gap energy. We have monitored the 4.3 eV absorption band, with temperature and obtained a thermal dependence of-0.026 meV/ºC. With this value we can predict the first and second order chromatic dispersion for a wavelength of 1550 nm.
Advanced Device Materials, 2014
ABSTRACT The spectral dynamics of a diffusive random laser under two photon excitation is investi... more ABSTRACT The spectral dynamics of a diffusive random laser under two photon excitation is investigated by using an experimental set-up which allows for fine mode discrimination and time resolution. The diffusive scattering system consists of a di-ureasil hybrid matrix powder doped with Rhodamine B. The anti-Stokes random laser emission obtained by pumping at 1064 nm shows a larger output pulse duration, build-up time, and threshold than the one produced under one photon pumping at 532 nm using the same experimental conditions. The time resolved analysis of the single shot emission pulse demonstrates the inherent stochastic nature of its lasing modes as well as the existence of modal relaxation oscillations. The outcome of our experiments also suggests that mode saturation appears with the increase of pump power.
Proceedings of SPIE - The International Society for Optical Engineering, 2011
Organic-inorganic hybrid materials are a technologically key class of advanced multifunctional ma... more Organic-inorganic hybrid materials are a technologically key class of advanced multifunctional materials that fulfil the challenging strict requirements of the beginning of the century: higher levels of sophistication, miniaturisation, recyclability, reliability and low energy consumption with potential to be used as low-cost components in optical networks operating at high bit rates. In this work, high-rejection optical filters (19 dB) first-order
Solid State Sciences, 2006
Zinc triflate (Zn(CF 3 SO 3) 2)-doped sol-gel derived di-urea cross-linked POE/siloxane ormolytes... more Zinc triflate (Zn(CF 3 SO 3) 2)-doped sol-gel derived di-urea cross-linked POE/siloxane ormolytes (designated as di-ureasils) with ∞ > n ≥ 1 (where the salt content is expressed as n, the molar ratio of oxyethylene moieties to Zn 2+ ions) were investigated. The hybrids with n ≥ 5 are entirely amorphous; those with n > 10 are thermally stable up to approximately 305 ºC. The siliceous network of representative samples (n = 200 and 10) is essentially composed of (SiO) 3 Si(CH 2)-environments and is thus highly branched. The distance between the structural units in samples with 200 ≥ n ≥ 10 and n ≤ 7 is 4.2 and 4.3 Å, respectively. The estimated interdomain distance is 11 and 13 Å for xerogels with 200 ≥ n ≥ 20 and n ≤ 10, respectively. At n = 1 a crystalline POE/Zn(CF 3 SO 3) 2 complex of unknown stoichiometry is formed. The conductivity maxima are located at n = 60 (3x10-6 S cm-1) and n = 20 (7x10-5 S cm-1) at 30 and 100 ºC, respectively.
The Journal of Physical Chemistry B, 2010
Three different types of photoluminescent hybrid materials containing trivalent lanthanide (Ln 3+... more Three different types of photoluminescent hybrid materials containing trivalent lanthanide (Ln 3+) Eu 3+ , Tb 3+) ions, chitosan, and silica have been prepared with different structural features. The different silica sources lead to diverse microstructures of hybrid materials, with silica being homogeneously dispersed in the chitosan materials (LnChS-H), or forming a core-shell morphology. Postsynthesis treatment is necessary for embedding the luminescent probe. The Ln 3+-based materials have been investigated by photoluminescence spectroscopy (12-300 K). The chitosan-Eu 3+-related local environment is maintained in the EuChS-H hybrid material. The emission features of the core-shell materials are characterized by the presence of two Eu 3+ distinct local environments, one associated with the chitosan core and the other with the silica shell.
Solid State Ionics, 2005
Poly(oxyethylene) (POE)/siloxane-based materials incorporating magnesium triflate (Mg(CF 3 SO 3) ... more Poly(oxyethylene) (POE)/siloxane-based materials incorporating magnesium triflate (Mg(CF 3 SO 3) 2) were synthesized by the sol-gel process. The host Class II hybrid matrix (diureasil) employed is composed of a siliceous framework to which short POE chains are covalently bonded through urea linkages. Ormolytes with salt composition n (molar ratio of oxyethylene moieties per Mg 2+ ion) ranging from ! to 1 were investigated. The nanohybrid with n = 20, which is thermally stable up to 360 ºC, exhibits the highest conductivity (e.g., approximately 4.0x10-6 and 6.7x10-5 "-1 cm-1 at 35 and 104 ºC, respectively). The redox stability domain of this material spans from-3.0 to +2.0 V versus Mg/Mg 2+ .
Química Nova, 2001
Recebido em 9/2/00; aceito em 22/11/00 Eu(III) LOCAL COORDINATION IN WHITE LIGHT EMITTERS ORGANIC... more Recebido em 9/2/00; aceito em 22/11/00 Eu(III) LOCAL COORDINATION IN WHITE LIGHT EMITTERS ORGANIC-INORGANIC HYBRIDS. Eu 3+ luminescence and EXAFS (Extended X-ray Absorption Fine Structure) results are presented for organic-inorganic hybrid gel hosts composed of a siliceous network to which small chains of oxyethylene units are covalently grafted by means of urea bridges. Coordination numbers for Eu 3+ ions range from 12.8 to 9.7 with increasing Eu 3+ concentration while the Eu 3+-first neighbours mean distance is found to be constant at 2.48-2.49 Å in the same concentration range. Emission spectra display a broad band in the green/blue spectral region superposed to narrow lines appearing in the yellow/red region in such a way that for the eyes emission appears white. The broad band is assigned to intrinsic NH groups emission and also to electron-hole recombination in the nanosised siliceous domains. The narrow lines are assigned to intra-4f 6 , 5 D 0 → 7 F 0-4 Eu 3+ transitions and from the energy position of the 7 F 0-4 levels a mean distance could be calculated for the Eu 3+-first neighbours. The calculated results are in good agreement with the experimental ones obtained from EXAFS analysis.
Polyhedron, 2003
New lanthanide complexes of 2-hydroxynicotinic acid (H2nicO)[Ln (HnicO) 2 (μ-HnicO)(H2O)]· nH2O (... more New lanthanide complexes of 2-hydroxynicotinic acid (H2nicO)[Ln (HnicO) 2 (μ-HnicO)(H2O)]· nH2O (Ln= Eu, Gd, Tb, Er, Tm) were prepared. The crystal structures of the [Tb (HnicO) 2 (μ-HnicO)(H2O)]· 1.75 H2O (1) and [Eu (HnicO) 2 (μ-HnicO)(H2O)]· 1.25 ...
Langmuir, 2012
Figure S1. DLS size distributions of AT-1.2 (blue), AT-1.1 (green) and AT-2.1 (red) NPs in water ... more Figure S1. DLS size distributions of AT-1.2 (blue), AT-1.1 (green) and AT-2.1 (red) NPs in water suspensions.
Journal of the Brazilian Chemical Society, 2006
Guias de luz planares foram obtidos a partir de um sol de um novo híbrido Ti 4+-acetilacetona (ac... more Guias de luz planares foram obtidos a partir de um sol de um novo híbrido Ti 4+-acetilacetona (acac)-Ureasil depositado na forma de filmes finos sobre substratos de vidro. A estrutura foi investigada por medidas espectroscópicas (absorção no infravermelho, fotoelétrons de raios-X e espalhamento Raman) e espalhamento de raios-X a baixos ângulos (SAXS). Para a adição do complexo Ti-acac ao ureasil na razão molar Ti:Si de 1:1 interações entre o complexo Ti-acac e grupos siloxanos foram identificadas. Quantidades maiores de Ti 4+ (razão molar Ti:Si de 5:1) levam também à formação de nanoagregados ricos em titânio. Os parâmetros ópticos dos guias, como índice de refração, espessura, modos propagados e coeficiente de atenuação foram medidos para 632,8, 543,5 e 1550 nm pela técnica de acoplamento de prisma. O índice de refração pode ser controlado pela quantidade relativa de titânio. Guias de poucos micra de espessura suportam modos de propagação com baixas perdas para todas as composições. Hybrid planar waveguides were prepared from Ti 4+-acetylacetone (acac)-Ureasil sols deposited on glass substrates. Structural features have been investigated by spectroscopic measurements (Fourier Transform Infrared Spectroscopy (FTIR), X-ray Photoelectron Spectroscopy (XPS) and Raman scattering) and Small Angle X-ray Scattering (SAXS). Addition of Ti 4+-acac to the ureasil (Ti:Si molar ratio 1:1) leads to the formation of bonds between the Ti complex and the siloxane groups, whereas further addition of Ti 4+ (Ti:Si molar ratio 5:1) leads to the additional formation of titanium-rich nanoclusters. The optical parameters of the waveguides such as refractive index, thickness, propagating modes and attenuation coefficient were measured at 632.8, 543.5 and 1550 nm by the prism coupling technique. The refractive index can be tuned by the Ti 4+ relative content. The few microns thick planar waveguides support well confined propagating modes with low attenuation loss for all compositions.
Journal of Materials Chemistry, 2012
This work reports on the infrared-to-visible CW frequency upconversion from planar waveguides bas... more This work reports on the infrared-to-visible CW frequency upconversion from planar waveguides based on Er 3+-Yb 3+-doped 100-xSiO 2-xTa 2 O 5 obtained by a sol-gel process and deposited onto a SiO 2-Si substrate by dip-coating. Surface morphology and optical parameters of the planar waveguides were analyzed by atomic force microscopy and the m-line technique. The influence of the composition on the electronic properties of the glass-ceramic films was followed by the band gap ranging from 4.35 to 4.51 eV upon modification of the Ta 2 O 5 content. Intense green and red emissions were detected from the upconversion process for all the samples after excitation at 980 nm. The relative intensities of the emission bands around 550 nm and 665 nm, assigned to the 2 H 11/2 / 4 I 15/2 , 4 S 3/2 / 4 I 15/2 , and 4 F 9/2 / 4 I 15/2 transitions, depended on the tantalum oxide content and the power of the laser source at 980 nm. The upconversion dynamics were investigated as a function of the Ta 2 O 5 content and the number of photons involved in each emission process. Based on the upconversion emission spectra and 1931CIE chromaticity diagram, it is shown that color can be tailored by composition and pump power. The glass ceramic films are attractive materials for application in upconversion lasers and near infrared-to-visible upconverters in solar cells.
Journal of Luminescence, 2005
The sol–gel method using metal alkoxide has been investigated to prepare aluminum–yttrium oxide a... more The sol–gel method using metal alkoxide has been investigated to prepare aluminum–yttrium oxide as yttrium–aluminum garnet (YAG) matrix composite fiber. In this paper we investigate the influence of yttrium content and temperature in the synthesis of Eu(III)-doped aluminum–yttrium oxide by non-hydrolytic sol–gel route. The formation process and the local structure of the samples were discussed by means of X-ray diffraction
Journal of Alloys and Compounds, 2004
Novel luminescent materials were prepared by introducing a new Eu 3+ complex of 2,6-dihydroxybenz... more Novel luminescent materials were prepared by introducing a new Eu 3+ complex of 2,6-dihydroxybenzoic acid (2,6-H 2 dhb) into a silica gel made by the sol-gel method. The crystal structure of the resulting complex [ n Bu 4 N] 2 [Eu(2,6-Hdhb) 5 (H 2 O) 2 ] was determined using single-crystal X-ray diffraction. The compound was further characterised using FTIR, FT-Raman and elemental analysis. Photoluminescence measurements were performed for the isolated Eu(III) 2,6-dihydroxybenzoate complex and also for the related silica composite material.
![Research paper thumbnail of Synthesis and crystal structure of [nBu4N][Er(pic)4]·5.5H2O: a new infrared emitter](https://attachments.academia-assets.com/101407597/thumbnails/1.jpg)
](Inorganic Chemistry Communications, 2003
The new erbium(III) complex of picolinic acid (Hpic), [ n Bu 4 N][Er(pic) 4 ] Á 5.5H 2 O, was syn... more The new erbium(III) complex of picolinic acid (Hpic), [ n Bu 4 N][Er(pic) 4 ] Á 5.5H 2 O, was synthesized and the crystal structure determined by single-crystal X-ray diffraction. The compound was further characterized using IR, Raman, 1 H NMR and elemental analysis. The picolinate ligands (pic À) are coordinated through N,O-chelation to the erbium cations, as shown by X-ray diffraction and spectroscopic results, leading to an eight coordinate complex. Photoluminescence measurements were performed for this compound which exhibits infrared emission.
Advanced Materials, 2010
A luminescent molecular thermometer for long-term absolute temperature measurements at the nanoscale
The sol-gel method using metal alkoxide has been investigated to prepare aluminum-yttrium oxide a... more The sol-gel method using metal alkoxide has been investigated to prepare aluminum-yttrium oxide as yttrium-aluminum garnet (YAG) matrix composite fiber. In this paper we investigate the influence of yttrium content and temperature in the synthesis of Eu(III)-doped aluminum-yttrium oxide by non-hydrolytic sol-gel route. The formation process and the local structure of the samples were discussed by means of X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and photoluminescence (PL) spectroscopy. For temperatures around 800 1C, initial crystallization was observed and the phases Y 4 Al 2 O 9 (YAM) and Y 3 Al 5 O 12 (YAG) appear. For samples treated at 800 and 1500 1C the emission spectra display preferentially the f-f transitions characteristic of the YAM monoclinic phase, whereas the YAG cubic appears as the favored phase at 1100 1C, in accordance with the Eu(III) centrosymmetrical local site. r
Inorganic Chemistry, 2006
Two calix[4]azacrowns, capped with two aminopolyamide bridges, were used as ligands for the compl... more Two calix[4]azacrowns, capped with two aminopolyamide bridges, were used as ligands for the complexation of lanthanide ions [Eu(III), Tb(III), Nd(III), Er(III), La(III)]. The formation of 1:2 and 1:1 complexes was observed, and stability constants, determined by UV absorption and fluorescence spectroscopy, were found to be generally on the order of log beta(11) approximately 5-6 and log beta(12) approximately 10. The structural changes of the ligands upon La(III) complexation were probed by 1H NMR spectroscopy. The two ligands were observed to have opposite fluorescence behaviors, namely, fluorescence enhancement (via blocking of photoinduced electron transfer from amine groups) or quenching (via lanthanide-chromophore interactions) upon metal ion complexation. Long-lived lanthanide luminescence was sensitized by excitation in the pi,pi band of the aromatic moieties of the ligands. The direct involvement of the antenna triplet state was demonstrated via quenching of the ligand phosphorescence by Tb(III). Generally, Eu(III) luminescence was weak (Phi(lum) &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;/= 0.01%) and much shorter lived (tau(lum) = 0.36 ms) than the Tb(III) emission. The latter, on the other hand, reached lifetimes of up to 2.60 ms and quantum yields as high as 12% for one of the ligands. Water/deuterium oxide exchange experiments showed the presence of only one solvent molecule in the coordination sphere of the lanthanides. However, Eu(III) luminescence was efficiently quenched by NH oscillators and the presence of a ligand-to-metal charge transfer state. Near-infrared luminescence of Nd(III) was also generated by energy-transfer sensitization.
Multifunctional materials working under solely visible-light are expected to play a significant r... more Multifunctional materials working under solely visible-light are expected to play a significant role in photo-electronics, in particular photo-switches, photo-optical sensors, smart windows, displays, optical storage memories, and self-cleaning materials.<div>In this work, we have modified the surface of a versatile semiconductor material (TiO<sub>2</sub>) with a noble metal (copper), and simultaneously doped its lattice with a rare-earth element (neodymium). Exploiting the ability of a semiconductor to generate an exciton upon excitation, a multifunctional material working with visible-light and showing photochromic, photoluminescent and photocatalytic activity was engineered. Advanced transmission electron microscopy techniques – aberration-corrected imaging combined with image simulation, statistical analyses and electron energy-loss spectroscopy – were used to characterise thoroughly the structure and local chemical environment as a function of the Nd<sup>...
Materials Science Forum, 2006
The main information transmission limitation in optical communications employing SiO 2 optical fi... more The main information transmission limitation in optical communications employing SiO 2 optical fibres is imposed by the optical pulses temporal broadening, resulting from the dispersive properties of the transmission medium (chromatic dispersion). Usually, this dispersion is modelled assuming a-0.4 meV/ºC dependence of the 11 eV gap energy. We have monitored the 4.3 eV absorption band, with temperature and obtained a thermal dependence of-0.026 meV/ºC. With this value we can predict the first and second order chromatic dispersion for a wavelength of 1550 nm.
Advanced Device Materials, 2014
ABSTRACT The spectral dynamics of a diffusive random laser under two photon excitation is investi... more ABSTRACT The spectral dynamics of a diffusive random laser under two photon excitation is investigated by using an experimental set-up which allows for fine mode discrimination and time resolution. The diffusive scattering system consists of a di-ureasil hybrid matrix powder doped with Rhodamine B. The anti-Stokes random laser emission obtained by pumping at 1064 nm shows a larger output pulse duration, build-up time, and threshold than the one produced under one photon pumping at 532 nm using the same experimental conditions. The time resolved analysis of the single shot emission pulse demonstrates the inherent stochastic nature of its lasing modes as well as the existence of modal relaxation oscillations. The outcome of our experiments also suggests that mode saturation appears with the increase of pump power.
Proceedings of SPIE - The International Society for Optical Engineering, 2011
Organic-inorganic hybrid materials are a technologically key class of advanced multifunctional ma... more Organic-inorganic hybrid materials are a technologically key class of advanced multifunctional materials that fulfil the challenging strict requirements of the beginning of the century: higher levels of sophistication, miniaturisation, recyclability, reliability and low energy consumption with potential to be used as low-cost components in optical networks operating at high bit rates. In this work, high-rejection optical filters (19 dB) first-order
Solid State Sciences, 2006
Zinc triflate (Zn(CF 3 SO 3) 2)-doped sol-gel derived di-urea cross-linked POE/siloxane ormolytes... more Zinc triflate (Zn(CF 3 SO 3) 2)-doped sol-gel derived di-urea cross-linked POE/siloxane ormolytes (designated as di-ureasils) with ∞ > n ≥ 1 (where the salt content is expressed as n, the molar ratio of oxyethylene moieties to Zn 2+ ions) were investigated. The hybrids with n ≥ 5 are entirely amorphous; those with n > 10 are thermally stable up to approximately 305 ºC. The siliceous network of representative samples (n = 200 and 10) is essentially composed of (SiO) 3 Si(CH 2)-environments and is thus highly branched. The distance between the structural units in samples with 200 ≥ n ≥ 10 and n ≤ 7 is 4.2 and 4.3 Å, respectively. The estimated interdomain distance is 11 and 13 Å for xerogels with 200 ≥ n ≥ 20 and n ≤ 10, respectively. At n = 1 a crystalline POE/Zn(CF 3 SO 3) 2 complex of unknown stoichiometry is formed. The conductivity maxima are located at n = 60 (3x10-6 S cm-1) and n = 20 (7x10-5 S cm-1) at 30 and 100 ºC, respectively.
The Journal of Physical Chemistry B, 2010
Three different types of photoluminescent hybrid materials containing trivalent lanthanide (Ln 3+... more Three different types of photoluminescent hybrid materials containing trivalent lanthanide (Ln 3+) Eu 3+ , Tb 3+) ions, chitosan, and silica have been prepared with different structural features. The different silica sources lead to diverse microstructures of hybrid materials, with silica being homogeneously dispersed in the chitosan materials (LnChS-H), or forming a core-shell morphology. Postsynthesis treatment is necessary for embedding the luminescent probe. The Ln 3+-based materials have been investigated by photoluminescence spectroscopy (12-300 K). The chitosan-Eu 3+-related local environment is maintained in the EuChS-H hybrid material. The emission features of the core-shell materials are characterized by the presence of two Eu 3+ distinct local environments, one associated with the chitosan core and the other with the silica shell.
Solid State Ionics, 2005
Poly(oxyethylene) (POE)/siloxane-based materials incorporating magnesium triflate (Mg(CF 3 SO 3) ... more Poly(oxyethylene) (POE)/siloxane-based materials incorporating magnesium triflate (Mg(CF 3 SO 3) 2) were synthesized by the sol-gel process. The host Class II hybrid matrix (diureasil) employed is composed of a siliceous framework to which short POE chains are covalently bonded through urea linkages. Ormolytes with salt composition n (molar ratio of oxyethylene moieties per Mg 2+ ion) ranging from ! to 1 were investigated. The nanohybrid with n = 20, which is thermally stable up to 360 ºC, exhibits the highest conductivity (e.g., approximately 4.0x10-6 and 6.7x10-5 "-1 cm-1 at 35 and 104 ºC, respectively). The redox stability domain of this material spans from-3.0 to +2.0 V versus Mg/Mg 2+ .
Química Nova, 2001
Recebido em 9/2/00; aceito em 22/11/00 Eu(III) LOCAL COORDINATION IN WHITE LIGHT EMITTERS ORGANIC... more Recebido em 9/2/00; aceito em 22/11/00 Eu(III) LOCAL COORDINATION IN WHITE LIGHT EMITTERS ORGANIC-INORGANIC HYBRIDS. Eu 3+ luminescence and EXAFS (Extended X-ray Absorption Fine Structure) results are presented for organic-inorganic hybrid gel hosts composed of a siliceous network to which small chains of oxyethylene units are covalently grafted by means of urea bridges. Coordination numbers for Eu 3+ ions range from 12.8 to 9.7 with increasing Eu 3+ concentration while the Eu 3+-first neighbours mean distance is found to be constant at 2.48-2.49 Å in the same concentration range. Emission spectra display a broad band in the green/blue spectral region superposed to narrow lines appearing in the yellow/red region in such a way that for the eyes emission appears white. The broad band is assigned to intrinsic NH groups emission and also to electron-hole recombination in the nanosised siliceous domains. The narrow lines are assigned to intra-4f 6 , 5 D 0 → 7 F 0-4 Eu 3+ transitions and from the energy position of the 7 F 0-4 levels a mean distance could be calculated for the Eu 3+-first neighbours. The calculated results are in good agreement with the experimental ones obtained from EXAFS analysis.
Polyhedron, 2003
New lanthanide complexes of 2-hydroxynicotinic acid (H2nicO)[Ln (HnicO) 2 (μ-HnicO)(H2O)]· nH2O (... more New lanthanide complexes of 2-hydroxynicotinic acid (H2nicO)[Ln (HnicO) 2 (μ-HnicO)(H2O)]· nH2O (Ln= Eu, Gd, Tb, Er, Tm) were prepared. The crystal structures of the [Tb (HnicO) 2 (μ-HnicO)(H2O)]· 1.75 H2O (1) and [Eu (HnicO) 2 (μ-HnicO)(H2O)]· 1.25 ...
Langmuir, 2012
Figure S1. DLS size distributions of AT-1.2 (blue), AT-1.1 (green) and AT-2.1 (red) NPs in water ... more Figure S1. DLS size distributions of AT-1.2 (blue), AT-1.1 (green) and AT-2.1 (red) NPs in water suspensions.
Journal of the Brazilian Chemical Society, 2006
Guias de luz planares foram obtidos a partir de um sol de um novo híbrido Ti 4+-acetilacetona (ac... more Guias de luz planares foram obtidos a partir de um sol de um novo híbrido Ti 4+-acetilacetona (acac)-Ureasil depositado na forma de filmes finos sobre substratos de vidro. A estrutura foi investigada por medidas espectroscópicas (absorção no infravermelho, fotoelétrons de raios-X e espalhamento Raman) e espalhamento de raios-X a baixos ângulos (SAXS). Para a adição do complexo Ti-acac ao ureasil na razão molar Ti:Si de 1:1 interações entre o complexo Ti-acac e grupos siloxanos foram identificadas. Quantidades maiores de Ti 4+ (razão molar Ti:Si de 5:1) levam também à formação de nanoagregados ricos em titânio. Os parâmetros ópticos dos guias, como índice de refração, espessura, modos propagados e coeficiente de atenuação foram medidos para 632,8, 543,5 e 1550 nm pela técnica de acoplamento de prisma. O índice de refração pode ser controlado pela quantidade relativa de titânio. Guias de poucos micra de espessura suportam modos de propagação com baixas perdas para todas as composições. Hybrid planar waveguides were prepared from Ti 4+-acetylacetone (acac)-Ureasil sols deposited on glass substrates. Structural features have been investigated by spectroscopic measurements (Fourier Transform Infrared Spectroscopy (FTIR), X-ray Photoelectron Spectroscopy (XPS) and Raman scattering) and Small Angle X-ray Scattering (SAXS). Addition of Ti 4+-acac to the ureasil (Ti:Si molar ratio 1:1) leads to the formation of bonds between the Ti complex and the siloxane groups, whereas further addition of Ti 4+ (Ti:Si molar ratio 5:1) leads to the additional formation of titanium-rich nanoclusters. The optical parameters of the waveguides such as refractive index, thickness, propagating modes and attenuation coefficient were measured at 632.8, 543.5 and 1550 nm by the prism coupling technique. The refractive index can be tuned by the Ti 4+ relative content. The few microns thick planar waveguides support well confined propagating modes with low attenuation loss for all compositions.
Journal of Materials Chemistry, 2012
This work reports on the infrared-to-visible CW frequency upconversion from planar waveguides bas... more This work reports on the infrared-to-visible CW frequency upconversion from planar waveguides based on Er 3+-Yb 3+-doped 100-xSiO 2-xTa 2 O 5 obtained by a sol-gel process and deposited onto a SiO 2-Si substrate by dip-coating. Surface morphology and optical parameters of the planar waveguides were analyzed by atomic force microscopy and the m-line technique. The influence of the composition on the electronic properties of the glass-ceramic films was followed by the band gap ranging from 4.35 to 4.51 eV upon modification of the Ta 2 O 5 content. Intense green and red emissions were detected from the upconversion process for all the samples after excitation at 980 nm. The relative intensities of the emission bands around 550 nm and 665 nm, assigned to the 2 H 11/2 / 4 I 15/2 , 4 S 3/2 / 4 I 15/2 , and 4 F 9/2 / 4 I 15/2 transitions, depended on the tantalum oxide content and the power of the laser source at 980 nm. The upconversion dynamics were investigated as a function of the Ta 2 O 5 content and the number of photons involved in each emission process. Based on the upconversion emission spectra and 1931CIE chromaticity diagram, it is shown that color can be tailored by composition and pump power. The glass ceramic films are attractive materials for application in upconversion lasers and near infrared-to-visible upconverters in solar cells.
Journal of Luminescence, 2005
The sol–gel method using metal alkoxide has been investigated to prepare aluminum–yttrium oxide a... more The sol–gel method using metal alkoxide has been investigated to prepare aluminum–yttrium oxide as yttrium–aluminum garnet (YAG) matrix composite fiber. In this paper we investigate the influence of yttrium content and temperature in the synthesis of Eu(III)-doped aluminum–yttrium oxide by non-hydrolytic sol–gel route. The formation process and the local structure of the samples were discussed by means of X-ray diffraction
Journal of Alloys and Compounds, 2004
Novel luminescent materials were prepared by introducing a new Eu 3+ complex of 2,6-dihydroxybenz... more Novel luminescent materials were prepared by introducing a new Eu 3+ complex of 2,6-dihydroxybenzoic acid (2,6-H 2 dhb) into a silica gel made by the sol-gel method. The crystal structure of the resulting complex [ n Bu 4 N] 2 [Eu(2,6-Hdhb) 5 (H 2 O) 2 ] was determined using single-crystal X-ray diffraction. The compound was further characterised using FTIR, FT-Raman and elemental analysis. Photoluminescence measurements were performed for the isolated Eu(III) 2,6-dihydroxybenzoate complex and also for the related silica composite material.
Inorganic Chemistry Communications, 2003
The new erbium(III) complex of picolinic acid (Hpic), [ n Bu 4 N][Er(pic) 4 ] Á 5.5H 2 O, was syn... more The new erbium(III) complex of picolinic acid (Hpic), [ n Bu 4 N][Er(pic) 4 ] Á 5.5H 2 O, was synthesized and the crystal structure determined by single-crystal X-ray diffraction. The compound was further characterized using IR, Raman, 1 H NMR and elemental analysis. The picolinate ligands (pic À) are coordinated through N,O-chelation to the erbium cations, as shown by X-ray diffraction and spectroscopic results, leading to an eight coordinate complex. Photoluminescence measurements were performed for this compound which exhibits infrared emission.
Advanced Materials, 2010
A luminescent molecular thermometer for long-term absolute temperature measurements at the nanoscale
The sol-gel method using metal alkoxide has been investigated to prepare aluminum-yttrium oxide a... more The sol-gel method using metal alkoxide has been investigated to prepare aluminum-yttrium oxide as yttrium-aluminum garnet (YAG) matrix composite fiber. In this paper we investigate the influence of yttrium content and temperature in the synthesis of Eu(III)-doped aluminum-yttrium oxide by non-hydrolytic sol-gel route. The formation process and the local structure of the samples were discussed by means of X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and photoluminescence (PL) spectroscopy. For temperatures around 800 1C, initial crystallization was observed and the phases Y 4 Al 2 O 9 (YAM) and Y 3 Al 5 O 12 (YAG) appear. For samples treated at 800 and 1500 1C the emission spectra display preferentially the f-f transitions characteristic of the YAM monoclinic phase, whereas the YAG cubic appears as the favored phase at 1100 1C, in accordance with the Eu(III) centrosymmetrical local site. r
Inorganic Chemistry, 2006
Two calix[4]azacrowns, capped with two aminopolyamide bridges, were used as ligands for the compl... more Two calix[4]azacrowns, capped with two aminopolyamide bridges, were used as ligands for the complexation of lanthanide ions [Eu(III), Tb(III), Nd(III), Er(III), La(III)]. The formation of 1:2 and 1:1 complexes was observed, and stability constants, determined by UV absorption and fluorescence spectroscopy, were found to be generally on the order of log beta(11) approximately 5-6 and log beta(12) approximately 10. The structural changes of the ligands upon La(III) complexation were probed by 1H NMR spectroscopy. The two ligands were observed to have opposite fluorescence behaviors, namely, fluorescence enhancement (via blocking of photoinduced electron transfer from amine groups) or quenching (via lanthanide-chromophore interactions) upon metal ion complexation. Long-lived lanthanide luminescence was sensitized by excitation in the pi,pi band of the aromatic moieties of the ligands. The direct involvement of the antenna triplet state was demonstrated via quenching of the ligand phosphorescence by Tb(III). Generally, Eu(III) luminescence was weak (Phi(lum) &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;/= 0.01%) and much shorter lived (tau(lum) = 0.36 ms) than the Tb(III) emission. The latter, on the other hand, reached lifetimes of up to 2.60 ms and quantum yields as high as 12% for one of the ligands. Water/deuterium oxide exchange experiments showed the presence of only one solvent molecule in the coordination sphere of the lanthanides. However, Eu(III) luminescence was efficiently quenched by NH oscillators and the presence of a ligand-to-metal charge transfer state. Near-infrared luminescence of Nd(III) was also generated by energy-transfer sensitization.