Luis Rino | University of Aveiro (original) (raw)
Papers by Luis Rino
With a 4f 6 electronic configuration, europium ions in the trivalent charge state are known to be... more With a 4f 6 electronic configuration, europium ions in the trivalent charge state are known to be efficient activators in wide band gap matrices. Embedded in the aluminophosphate (Li 2 O–BaO–Al 2 O 3 –La 2 O 3 – P 2 O 5) glasses the optically activated Eu 3 þ ions lead to intense room temperature orange/red lumines-cence with 16–23 Cd/m 2 by using ultraviolet pumping. The as-prepared and heat treated europium doped glasses for temperatures below and above T g were studied by room temperature Raman spectroscopy, absorption, photoluminescence excitation, temperature dependent and time dependent photoluminescence. When the samples are excited by 325 nm wavelength photons, an enhancement of the red luminescence intensity by ca. one order of magnitude was found to occur for temperatures between 14 K and 350 K, for all the doped glasses. On the other hand, by using resonant excitation on the 5 L 6 Eu 3 þ excited state (λ exc $ 390 nm) the ion emission intensity was found to be nearly constant for temperatures up to 500 K. For higher temperatures a steeper decrease of the luminescence intensity occurs due to non-radiative competitive channels described by activation energies of ca. 235 meV and 450 meV by using 325 and 390 nm wavelength photons as excitation, respectively. The lifetime of the 5 D 0 level in these glasses is ca. 2.93 ms. A discussion of the thermal population and de-excitation mechanisms is performed.
Niobium oxides have been reported as an alternative to tantalum, and its oxide, for the productio... more Niobium oxides have been reported as an alternative to tantalum, and its oxide, for the production of capacitors, but these materials still require a further and exhaustive study. Understanding the dynamics of the oxidation process from NbO to Nb 2 O 5 is essential to explain and control the properties of a niobium oxide based capacitors. In situ XRD analysis of NbO powders was performed from 100 to 1100 • C, which showed a temperature range where only amorphous phase is present. The capacitor anodes, formed from the same type of NbO powders, were then heat-treated in air from room-temperature (RT) to 550 • C and recorded with a video camera to see the colour shift. The presence of core–shell structures and the increase of the shell thickness/amount with temperature are visible in SEM. Finally, in situ spectroscopy studies were performed, in order to observe the interference spectra which are responsible for the observed colours.
With a 4f 6 electronic configuration, europium ions in the trivalent charge state are known to be... more With a 4f 6 electronic configuration, europium ions in the trivalent charge state are known to be efficient activators in wide band gap matrices. Embedded in the aluminophosphate (Li 2 O–BaO–Al 2 O 3 –La 2 O 3 – P 2 O 5) glasses the optically activated Eu 3 þ ions lead to intense room temperature orange/red lumines-cence with 16–23 Cd/m 2 by using ultraviolet pumping. The as-prepared and heat treated europium doped glasses for temperatures below and above T g were studied by room temperature Raman spectroscopy, absorption, photoluminescence excitation, temperature dependent and time dependent photoluminescence. When the samples are excited by 325 nm wavelength photons, an enhancement of the red luminescence intensity by ca. one order of magnitude was found to occur for temperatures between 14 K and 350 K, for all the doped glasses. On the other hand, by using resonant excitation on the 5 L 6 Eu 3 þ excited state (λ exc $ 390 nm) the ion emission intensity was found to be nearly constant for temperatures up to 500 K. For higher temperatures a steeper decrease of the luminescence intensity occurs due to non-radiative competitive channels described by activation energies of ca. 235 meV and 450 meV by using 325 and 390 nm wavelength photons as excitation, respectively. The lifetime of the 5 D 0 level in these glasses is ca. 2.93 ms. A discussion of the thermal population and de-excitation mechanisms is performed.
Li 2 O–BaO–Al 2 O 3 –La 2 O 3 –P 2 O 5 glasses optically activated with rare earth ions with the ... more Li 2 O–BaO–Al 2 O 3 –La 2 O 3 –P 2 O 5 glasses optically activated with rare earth ions with the 4f 5 , and 4f 8 electronic configuration (Sm 3+ and Tb 3+ , respectively) were analyzed by Raman spectroscopy, absorption, excitation photoluminescence, decay curves and temperature dependent photoluminescence. The spec-troscopic characteristics of the as-prepared and heat treated samples at temperatures below and above T g were studied as well as their room temperature photometric properties under ultraviolet excitation. All the doped glasses exhibit typical signatures of the lanthanides in their trivalent charge state. For the samarium doped glass heat treated at 250 °C (<T g) the Sm 2+ luminescence was also observed. The analysis of the luminescence efficiency was performed in the interval range of 14 K to room temperature, where the integrated intensity of the luminescence was found to decrease for the Sm 3+ and Tb 3+ ions in the studied temperature range. Luminescence decay curves were found to be non-exponential for the 4 G 5/2 ? 6 H 7/2 and 5 D 3 ? 7 F 4 transitions of the Sm 3+ and Tb 3+ ions, respectively. The results strongly suggest the occurrence of energy transfer processes through cross relaxation phenomena, mediated by dipole–dipole interaction in all the studied samples. The decay of the 5 D 4 ? 7 F 5 emission of the Tb 3+ ions was found to be single exponential with a time constant of $3.1 ms. Based on the spectroscopic characteristics, models for recombination processes are proposed. The room temperature luminance photometric properties with ultraviolet excitation show that the samarium doped glasses have much lower luminance intensity (around 0.3 Cd/m 2) when compared with the 6–7 Cd/m 2 observed for the terbium doped ones.
Applied Physics A, 2013
Blends of Si nanocrystals (Si-NCs) and organic semiconductors are promising materials for new opt... more Blends of Si nanocrystals (Si-NCs) and organic semiconductors are promising materials for new optical and electronic devices processed from solutions. Here, we study how the optical properties of composite films containing Si-NCs and the organic semiconductor poly(3-hexylthiophene) (P3HT) are influenced by the composition and morphology resulting from different solution-processing parameters and different solvents used dichlorobenzene vs. chloroform). The optical spectra of the hybrid films are described using a simple phenomenological model, with which we can discern the contribution of each material in the films to the optical properties. From this analysis, we obtain quantitative information about the composition and morphology of the hybrid nanostructured films, which otherwise would be obtained from more demanding microscopy and
Novel nanomaterials and new nanotechnology applications are cornerstones of innovative high value... more Novel nanomaterials and new nanotechnology applications are cornerstones of innovative high value-added products in several industrial fields. From a technological point a view, there is a strong demand for techniques to fabricate and measure the properties of these nanomaterials and related devices. In parallel, at a more fundamental level, a higher comprehension of the materials physical properties at the nanoscale level is needed. Properties of these novel materials depend on a myriad of parameters. As an example optical properties will depend on such as feature size, shape, surface characteristics, interaction with the surrounding environment, etc. Characterization of nanomaterials employs expensive high-tech equipment combined with multidisciplinary teams of experts that cannot usually be accommodated in a Small to Medium-sized Enterprise budget. This talk will address the advantages for the industry, mainly SMEs to partnership with established academic laboratories in order to...
Scientific Reports
In this work we demonstrate by photoluminescence studies white light emission from a monolithic I... more In this work we demonstrate by photoluminescence studies white light emission from a monolithic InGaN/GaN single quantum well structure grown by metal organic chemical vapour deposition. As-grown and thermally annealed samples at high temperature (1000 °C, 1100 °C and 1200 °C) and high pressure (1.1 GPa) were analysed by spectroscopic techniques, and the annealing effect on the photoluminescence is deeply explored. Under laser excitation of 3.8 eV at room temperature, the as-grown structure exhibits two main emission bands: a yellow band peaked at 2.14 eV and a blue band peaked at 2.8 eV resulting in white light perception. Interestingly, the stability of the white light is preserved after annealing at the lowest temperature (1000 °C), but suppressed for higher temperatures due to a deterioration of the blue quantum well emission. Moreover, the control of the yellow/blue bands intensity ratio, responsible for the white colour coordinate temperatures, could be achieved after annealin...
Journal of the European Ceramic Society
Garnet structures are widely used to produce white-lighting phosphors in the LED industry since b... more Garnet structures are widely used to produce white-lighting phosphors in the LED industry since bright-blue (Ga,In)N sources became available, Yttrium aluminium garnet doped with cerium ions (YAG:Ce) being the most prominent due to the Ce3+ yellow emission combination with the blue emission of the (Ga,In)N chip. When excited in the near UV, Dy3+ ions can also emit strong blue and yellow bands and if incorporated in a suitable host, they are good candidates for white-lighting phosphors. Here, we present a variation of the solution synthesis combustion technique with two fuels combination that can be used to directly synthesize YAG:Dy nanopowders with crystallite sizes of about 40 nm. This process allow the production of the single phase YAG:Dy at low temperature and time load with minimum energy consumption, without the usual need of any post synthesis heat treatments, as confirmed by X-ray diffraction and Raman spectroscopy measurements. Photoluminescence measurements confirmed the ...
Broad blue band from the β-Ga 2 O 3 host 3 .
Physica Status Solidi C: Current Topics in Solid State Physics, Vol 10, No 4, 2013
physica status solidi (b), 2013
ABSTRACT Intra-4f12 transitions of Tm3+ ions in zirconia powders processed by solution combustion... more ABSTRACT Intra-4f12 transitions of Tm3+ ions in zirconia powders processed by solution combustion synthesis (CS) were studied by optical techniques. The results were compared with the ones obtained in reference samples of yttria stabilized zirconia fibers grown by laser floating zone. The spectroscopic features observed for the tetragonal fibre were compared with the Stark lines detected in the polyphasic (monoclinic and tetragonal) powder suggesting additional Tm3+ sites/environments due to the ions in the monoclinic host. The stability of the blue 1D2 → 3F4 and red 1G4 → 3H6 transitions was found to be strongly dependent on temperature. For the fibres, the blue luminescence increases by a factor of two between 15 K and the room temperature when pumping the sample in the 1D2 level. When the excitation is performed in the 1G4 state a higher stability of the red luminescence was found to occur in fibres than in the polyphasic powder. Constant 1G4 → 3H6 integrated intensity was observed in the fibres, while a decrease of the red luminescence efficiency occurs with temperature for the polyphasic powder. The suppression of the nonradiative paths which compete with the radiative transition could be attained by using thulium doped yttria stabilized CS powders.
Journal of the European Ceramic Society, 2013
ABSTRACT Niobium oxides have been reported as an alternative to tantalum, and its oxide, for the ... more ABSTRACT Niobium oxides have been reported as an alternative to tantalum, and its oxide, for the production of capacitors, but these materials still require a further and exhaustive study. Understanding the dynamics of the oxidation process from NbO to Nb2O5 is essential to explain and control the properties of a niobium oxide based capacitors. In situ XRD analysis of NbO powders was performed from 100 to 1100 °C, which showed a temperature range where only amorphous phase is present. The capacitor anodes, formed from the same type of NbO powders, were then heat-treated in air from room-temperature (RT) to 550 °C and recorded with a video camera to see the colour shift. The presence of core–shell structures and the increase of the shell thickness/amount with temperature are visible in SEM. Finally, in situ spectroscopy studies were performed, in order to observe the interference spectra which are responsible for the observed colours.
Journal of Materials Chemistry, 2011
... Dysprosium doped yttria stabilized zirconia single crystals grown by the laser floating zone ... more ... Dysprosium doped yttria stabilized zirconia single crystals grown by the laser floating zone method crystallize in the tetragonal form as confirmed by Raman spectroscopy. ... 3, S. Nakamura, The BlueLaser Diode: The Complete Story, Springer, Berlin, NewYork, 2nd edn, 2000 . ...
European Journal of Inorganic Chemistry, 2014
With a 4f 6 electronic configuration, europium ions in the trivalent charge state are known to be... more With a 4f 6 electronic configuration, europium ions in the trivalent charge state are known to be efficient activators in wide band gap matrices. Embedded in the aluminophosphate (Li 2 O–BaO–Al 2 O 3 –La 2 O 3 – P 2 O 5) glasses the optically activated Eu 3 þ ions lead to intense room temperature orange/red lumines-cence with 16–23 Cd/m 2 by using ultraviolet pumping. The as-prepared and heat treated europium doped glasses for temperatures below and above T g were studied by room temperature Raman spectroscopy, absorption, photoluminescence excitation, temperature dependent and time dependent photoluminescence. When the samples are excited by 325 nm wavelength photons, an enhancement of the red luminescence intensity by ca. one order of magnitude was found to occur for temperatures between 14 K and 350 K, for all the doped glasses. On the other hand, by using resonant excitation on the 5 L 6 Eu 3 þ excited state (λ exc $ 390 nm) the ion emission intensity was found to be nearly constant for temperatures up to 500 K. For higher temperatures a steeper decrease of the luminescence intensity occurs due to non-radiative competitive channels described by activation energies of ca. 235 meV and 450 meV by using 325 and 390 nm wavelength photons as excitation, respectively. The lifetime of the 5 D 0 level in these glasses is ca. 2.93 ms. A discussion of the thermal population and de-excitation mechanisms is performed.
Niobium oxides have been reported as an alternative to tantalum, and its oxide, for the productio... more Niobium oxides have been reported as an alternative to tantalum, and its oxide, for the production of capacitors, but these materials still require a further and exhaustive study. Understanding the dynamics of the oxidation process from NbO to Nb 2 O 5 is essential to explain and control the properties of a niobium oxide based capacitors. In situ XRD analysis of NbO powders was performed from 100 to 1100 • C, which showed a temperature range where only amorphous phase is present. The capacitor anodes, formed from the same type of NbO powders, were then heat-treated in air from room-temperature (RT) to 550 • C and recorded with a video camera to see the colour shift. The presence of core–shell structures and the increase of the shell thickness/amount with temperature are visible in SEM. Finally, in situ spectroscopy studies were performed, in order to observe the interference spectra which are responsible for the observed colours.
With a 4f 6 electronic configuration, europium ions in the trivalent charge state are known to be... more With a 4f 6 electronic configuration, europium ions in the trivalent charge state are known to be efficient activators in wide band gap matrices. Embedded in the aluminophosphate (Li 2 O–BaO–Al 2 O 3 –La 2 O 3 – P 2 O 5) glasses the optically activated Eu 3 þ ions lead to intense room temperature orange/red lumines-cence with 16–23 Cd/m 2 by using ultraviolet pumping. The as-prepared and heat treated europium doped glasses for temperatures below and above T g were studied by room temperature Raman spectroscopy, absorption, photoluminescence excitation, temperature dependent and time dependent photoluminescence. When the samples are excited by 325 nm wavelength photons, an enhancement of the red luminescence intensity by ca. one order of magnitude was found to occur for temperatures between 14 K and 350 K, for all the doped glasses. On the other hand, by using resonant excitation on the 5 L 6 Eu 3 þ excited state (λ exc $ 390 nm) the ion emission intensity was found to be nearly constant for temperatures up to 500 K. For higher temperatures a steeper decrease of the luminescence intensity occurs due to non-radiative competitive channels described by activation energies of ca. 235 meV and 450 meV by using 325 and 390 nm wavelength photons as excitation, respectively. The lifetime of the 5 D 0 level in these glasses is ca. 2.93 ms. A discussion of the thermal population and de-excitation mechanisms is performed.
Li 2 O–BaO–Al 2 O 3 –La 2 O 3 –P 2 O 5 glasses optically activated with rare earth ions with the ... more Li 2 O–BaO–Al 2 O 3 –La 2 O 3 –P 2 O 5 glasses optically activated with rare earth ions with the 4f 5 , and 4f 8 electronic configuration (Sm 3+ and Tb 3+ , respectively) were analyzed by Raman spectroscopy, absorption, excitation photoluminescence, decay curves and temperature dependent photoluminescence. The spec-troscopic characteristics of the as-prepared and heat treated samples at temperatures below and above T g were studied as well as their room temperature photometric properties under ultraviolet excitation. All the doped glasses exhibit typical signatures of the lanthanides in their trivalent charge state. For the samarium doped glass heat treated at 250 °C (<T g) the Sm 2+ luminescence was also observed. The analysis of the luminescence efficiency was performed in the interval range of 14 K to room temperature, where the integrated intensity of the luminescence was found to decrease for the Sm 3+ and Tb 3+ ions in the studied temperature range. Luminescence decay curves were found to be non-exponential for the 4 G 5/2 ? 6 H 7/2 and 5 D 3 ? 7 F 4 transitions of the Sm 3+ and Tb 3+ ions, respectively. The results strongly suggest the occurrence of energy transfer processes through cross relaxation phenomena, mediated by dipole–dipole interaction in all the studied samples. The decay of the 5 D 4 ? 7 F 5 emission of the Tb 3+ ions was found to be single exponential with a time constant of $3.1 ms. Based on the spectroscopic characteristics, models for recombination processes are proposed. The room temperature luminance photometric properties with ultraviolet excitation show that the samarium doped glasses have much lower luminance intensity (around 0.3 Cd/m 2) when compared with the 6–7 Cd/m 2 observed for the terbium doped ones.
Applied Physics A, 2013
Blends of Si nanocrystals (Si-NCs) and organic semiconductors are promising materials for new opt... more Blends of Si nanocrystals (Si-NCs) and organic semiconductors are promising materials for new optical and electronic devices processed from solutions. Here, we study how the optical properties of composite films containing Si-NCs and the organic semiconductor poly(3-hexylthiophene) (P3HT) are influenced by the composition and morphology resulting from different solution-processing parameters and different solvents used dichlorobenzene vs. chloroform). The optical spectra of the hybrid films are described using a simple phenomenological model, with which we can discern the contribution of each material in the films to the optical properties. From this analysis, we obtain quantitative information about the composition and morphology of the hybrid nanostructured films, which otherwise would be obtained from more demanding microscopy and
Novel nanomaterials and new nanotechnology applications are cornerstones of innovative high value... more Novel nanomaterials and new nanotechnology applications are cornerstones of innovative high value-added products in several industrial fields. From a technological point a view, there is a strong demand for techniques to fabricate and measure the properties of these nanomaterials and related devices. In parallel, at a more fundamental level, a higher comprehension of the materials physical properties at the nanoscale level is needed. Properties of these novel materials depend on a myriad of parameters. As an example optical properties will depend on such as feature size, shape, surface characteristics, interaction with the surrounding environment, etc. Characterization of nanomaterials employs expensive high-tech equipment combined with multidisciplinary teams of experts that cannot usually be accommodated in a Small to Medium-sized Enterprise budget. This talk will address the advantages for the industry, mainly SMEs to partnership with established academic laboratories in order to...
Scientific Reports
In this work we demonstrate by photoluminescence studies white light emission from a monolithic I... more In this work we demonstrate by photoluminescence studies white light emission from a monolithic InGaN/GaN single quantum well structure grown by metal organic chemical vapour deposition. As-grown and thermally annealed samples at high temperature (1000 °C, 1100 °C and 1200 °C) and high pressure (1.1 GPa) were analysed by spectroscopic techniques, and the annealing effect on the photoluminescence is deeply explored. Under laser excitation of 3.8 eV at room temperature, the as-grown structure exhibits two main emission bands: a yellow band peaked at 2.14 eV and a blue band peaked at 2.8 eV resulting in white light perception. Interestingly, the stability of the white light is preserved after annealing at the lowest temperature (1000 °C), but suppressed for higher temperatures due to a deterioration of the blue quantum well emission. Moreover, the control of the yellow/blue bands intensity ratio, responsible for the white colour coordinate temperatures, could be achieved after annealin...
Journal of the European Ceramic Society
Garnet structures are widely used to produce white-lighting phosphors in the LED industry since b... more Garnet structures are widely used to produce white-lighting phosphors in the LED industry since bright-blue (Ga,In)N sources became available, Yttrium aluminium garnet doped with cerium ions (YAG:Ce) being the most prominent due to the Ce3+ yellow emission combination with the blue emission of the (Ga,In)N chip. When excited in the near UV, Dy3+ ions can also emit strong blue and yellow bands and if incorporated in a suitable host, they are good candidates for white-lighting phosphors. Here, we present a variation of the solution synthesis combustion technique with two fuels combination that can be used to directly synthesize YAG:Dy nanopowders with crystallite sizes of about 40 nm. This process allow the production of the single phase YAG:Dy at low temperature and time load with minimum energy consumption, without the usual need of any post synthesis heat treatments, as confirmed by X-ray diffraction and Raman spectroscopy measurements. Photoluminescence measurements confirmed the ...
Broad blue band from the β-Ga 2 O 3 host 3 .
Physica Status Solidi C: Current Topics in Solid State Physics, Vol 10, No 4, 2013
physica status solidi (b), 2013
ABSTRACT Intra-4f12 transitions of Tm3+ ions in zirconia powders processed by solution combustion... more ABSTRACT Intra-4f12 transitions of Tm3+ ions in zirconia powders processed by solution combustion synthesis (CS) were studied by optical techniques. The results were compared with the ones obtained in reference samples of yttria stabilized zirconia fibers grown by laser floating zone. The spectroscopic features observed for the tetragonal fibre were compared with the Stark lines detected in the polyphasic (monoclinic and tetragonal) powder suggesting additional Tm3+ sites/environments due to the ions in the monoclinic host. The stability of the blue 1D2 → 3F4 and red 1G4 → 3H6 transitions was found to be strongly dependent on temperature. For the fibres, the blue luminescence increases by a factor of two between 15 K and the room temperature when pumping the sample in the 1D2 level. When the excitation is performed in the 1G4 state a higher stability of the red luminescence was found to occur in fibres than in the polyphasic powder. Constant 1G4 → 3H6 integrated intensity was observed in the fibres, while a decrease of the red luminescence efficiency occurs with temperature for the polyphasic powder. The suppression of the nonradiative paths which compete with the radiative transition could be attained by using thulium doped yttria stabilized CS powders.
Journal of the European Ceramic Society, 2013
ABSTRACT Niobium oxides have been reported as an alternative to tantalum, and its oxide, for the ... more ABSTRACT Niobium oxides have been reported as an alternative to tantalum, and its oxide, for the production of capacitors, but these materials still require a further and exhaustive study. Understanding the dynamics of the oxidation process from NbO to Nb2O5 is essential to explain and control the properties of a niobium oxide based capacitors. In situ XRD analysis of NbO powders was performed from 100 to 1100 °C, which showed a temperature range where only amorphous phase is present. The capacitor anodes, formed from the same type of NbO powders, were then heat-treated in air from room-temperature (RT) to 550 °C and recorded with a video camera to see the colour shift. The presence of core–shell structures and the increase of the shell thickness/amount with temperature are visible in SEM. Finally, in situ spectroscopy studies were performed, in order to observe the interference spectra which are responsible for the observed colours.
Journal of Materials Chemistry, 2011
... Dysprosium doped yttria stabilized zirconia single crystals grown by the laser floating zone ... more ... Dysprosium doped yttria stabilized zirconia single crystals grown by the laser floating zone method crystallize in the tetragonal form as confirmed by Raman spectroscopy. ... 3, S. Nakamura, The BlueLaser Diode: The Complete Story, Springer, Berlin, NewYork, 2nd edn, 2000 . ...
European Journal of Inorganic Chemistry, 2014