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Papers by José Germino

Disentangling X‐Ray and Sunlight Irradiation Effects Under a Controllable Atmosphere in Metal Halide Perovskites

Solar RRL

Metal halide perovskites are versatile materials for photovoltaic and optoelectronic applications... more Metal halide perovskites are versatile materials for photovoltaic and optoelectronic applications owing to their adjustable bandgap and emission properties. Nevertheless, a drawback is their photo‐structural–chemical instability. Herein, structural and optical responses of metal halide perovskite films, exploiting in situ X‐ray and visible light stimuli under dry and humid atmospheres, are correlated. It shows that the interplay of the physical parameters responsible for sample evolution depends in a nontrivial way on the nature of the excitation, radiation power density, and moisture conditions. Two perovskite samples demonstrate the relevance of each composition. They are resilient under a dry atmosphere, but the presence of water or oxygen molecules in the ambient air leads to structural and optical changes under irradiation. However, the sample reaction depends on the photons’ excitation energy and power density to be effective. Under a dry atmosphere, the halide segregation inv...

Journal of the Brazilian Chemical Society

Sustainable energy generation has been a growing concern worldwide due to the alarming effects of... more Sustainable energy generation has been a growing concern worldwide due to the alarming effects of climate changes in the last few decades. In this scenario, perovskite solar cells hold great promise in contributing for a greener global energy matrix. Despite the great potential of this technology, several difficulties to deploy perovskite solar panels are yet to be overcome, being their long-term stability one of the most critical. In this sense, this work offers an alternative to improve the long-term, operational stability of the devices by passivating the CsFAMA perovskite active layer with a mixture of N-(2-aminoethyl)naphthalimide and mercaptopropionic acid. These modifications improved the perovskite and device stability under ambient conditions. The solar cells without encapsulation and with post-treatment with 5 mM modifier solution retained ca. 90% of its initial power conversion efficiency (PCE) after 500 h exposed to ambient conditions, while standard solar cells retained...

Light-induced halide segregation in perovskites with wrinkled morphology

Journal of Energy Chemistry

New strategies for the improvement of the photo and electroluminescent properties of Zn(II) and Pt(II) Salicylidenes

Color tunable hybrid light-emitting diodes based on perovskite quantum dot/conjugated polymer

Inorganic organic metal halide perovskite materials have been investigated for several technologi... more Inorganic organic metal halide perovskite materials have been investigated for several technological applications, such as photovoltaic cells, lasers, photodetectors and light emitting diodes (LEDs), either in the bulk form or as colloidal nanoparticles. Recently, all inorganic Cesium Lead Halide (CsPbX3, X=Cl,Br, I) perovskite quantum dots (PQDs) were reported with high photoluminescence quantum yield with narrow emission lines in the visible wavelengths. Here, green-emitting perovskite quantum dots (PQDs) prepared by a synthetic method based on a mixture of oleylamine and oleic acid as surfactants were applied in the electroluminescent layer of hybrid LEDs in combination with two different conjugated polymers: polyvinylcarbazole (PVK) or poly(9,9-di-n-octylfluorenyl-2,7-diyl) (PFO). The performance of the diodes and the emission color tuning upon dispersion of different concentrations of the PQDs in the polymer matrix is discussed. The presented approach aims at the combination of...

Effect of the Zn coordination complex on the excited-state and two-photon absorption spectra of a novel sallicylidene compound

Developing solid state NIR emitters and simultaneously discriminative detection trace water in or... more Developing solid state NIR emitters and simultaneously discriminative detection trace water in organic solvents has long been a significant challenge. In this work, a novel diketopyrrolopyrrole-based luminogen (DPP1) with excited state intramolecular proton transfer (ESIPT) and aggregation-induced emission (AIE) characteristics has been designed and synthesized. Its amorphous and crystal solids show red and NIR-emissive fluorescence at 625 nm and 675 nm, respectively. When DPP1 reacted with fluoride anion, the resulting system (DPP1.F) can discriminatively detect water content in aprotic solvents with colorimetric and fluorescent dual-modes. Distinct fluorescent responses of "turn on", "ratiometric turn off", "ratiometric turn on" and low limit of detection of 0.0064 v%, 0.042 v% and 0.192 v% in THF, acetone, and acetonitrile were obtained, respectively. The water-induced sensitive and fast change in THF was applied to the determination of water in foodstuffs in practical solid-state indicator paper strips.

Journal of Materials Chemistry C, 2021

Correction for ‘Reduced graphene oxide in perovskite solar cells: the influence on film formation... more Correction for ‘Reduced graphene oxide in perovskite solar cells: the influence on film formation, photophysics, performance, and stability’ by Paulo Ernesto Marchezi et al., J. Mater. Chem. C, 2021, DOI: 10.1039/D1TC01360B.

Journal of Luminescence, 2021

′-bipyridylene)vinylene-alt-2,5-(1,4-bis(octyloxy)vinylene)] (PBPyVOctV), was synthesized by the ... more ′-bipyridylene)vinylene-alt-2,5-(1,4-bis(octyloxy)vinylene)] (PBPyVOctV), was synthesized by the polymerization of 5,5 ′-divinyl-2,2 ′-bipyridine with 1,4-dibromo-2,5-bis(octyloxy) benzene through a Heck cross-coupling reaction. Then, a metallopolymer, PBPyVOctV-Eu(tta) 3 , was obtained by the bipyridine chelating coordination of PBPyVOctV with europium (Eu(III)) complex, Eu(tta) 3 .xH 2 O (where tta is 2thenoyltrifluoroacetonate). The incorporation of an europium center into the polymer backbone changed the optical and electronic properties of the conjugated polymer. The photoluminescence of the materials and electroluminescence properties of solution-processed organic light-emitting diodes (OLEDs) consisting of composites of PVK as a host with PBPyVOctV, Eu(tta) 3 .xH 2 O or PBPyVOctV-Eu(tta) 3 as guests were studied. The diode containing PVK:PBPyVOctV-Eu(tta) 3 as emissive layer delivered the highest luminance and highest current efficiency, with an orange color emission, as a result of combined emissions from the europium ions and polymer structure.

Angewandte Chemie International Edition, 2020

Angabe der unten stehenden Digitalobjekt-Identifizierungsnummer (DOI) zitiert werden. Die deutsch... more Angabe der unten stehenden Digitalobjekt-Identifizierungsnummer (DOI) zitiert werden. Die deutsche Übersetzung wird gemeinsam mit der endgültigen englischen Fassung erscheinen. Die endgültige englische Fassung (Version of Record) wird ehestmöglich nach dem Redigieren und einem Korrekturgang als Early-View-Beitrag erscheinen und kann sich naturgemäß von der AA-Fassung unterscheiden. Leser sollten daher die endgültige Fassung, sobald sie veröffentlicht ist, verwenden. Für die AA-Fassung trägt der Autor die alleinige Verantwortung.

Materials Research, 2019

Carbon dots (C-dots) possess the attractive properties of high stability, low toxicity, good wate... more Carbon dots (C-dots) possess the attractive properties of high stability, low toxicity, good water solubility, simple synthetic routes as well as size and excitation-dependent photoluminescence (PL).The aim of this work was to synthesize photoluminescent C-dots by hydrothermal method using acerola fruit (Malpighiaemarginata) as a row material, since this fruit contains large number of organic molecules. Studies about the optimal synthesis conditions were performed, where these organic molecules were converted into C-dots by hydrothermal carbonization at 180 ºC for 18 h. The C-dots exhibited a green emission light at 459 nm when excited under UV-light (λ ex = 370 nm). These nanomaterials were also successfully used to prepare C-dots/poly (vinyl alcohol) luminescent composites (C-dots/PVA). Both C-dots and C-dots/PVA composite films were investigated by using colorimetric visual sensor for Fe 3+ metal ions detection. The results show that the prepared C-dots and C-dots/poly presented strong green emission light. The emission spectra of above materials were quenched in the presence of Fe 3+ ions. Thus, highly specific "turn off" fluorescence sensing of Fe 3+ was achieved using fluorescent C-dots. Regarding, this work describe that the polymeric films as sensors of metallic ions in aqueous solution appears as a new perspectives to design new composite materials.

Journal of Luminescence, 2018

The photo-and electroluminescent properties of a copolymer containing fluorene, terpyridine and c... more The photo-and electroluminescent properties of a copolymer containing fluorene, terpyridine and complexed sites with trivalent europium ions (LaPPS66Eu) was 2 investigated. The non-complexed backbone (LaPPS66) and an analogous chemical structure of the ligand/Eu 3+ site (LaPPS66M) as a model compound were used for comparison and interpretation of the photophysical properties. Experiments were carried out using PVK as a dispersive matrix either in a blend form or in a bilayer configuration. Absorption and emission spectra, time-resolved emission spectra (TRES) and Förster Resonance Energy Transfer efficiency () were used to account for the differences found for the photophysical properties of each configuration.

Química Nova, 2017

NEW HYBRIDS BASED ON IRON (III) OXYHYDROXIDE AND GOLD NANOPARTICLES (AuNPs / FeOOH) as CATALYSTS ... more NEW HYBRIDS BASED ON IRON (III) OXYHYDROXIDE AND GOLD NANOPARTICLES (AuNPs / FeOOH) as CATALYSTS FOR THE REDUCTION OF ORGANIC ENVIRONMENTAL POLLUTANTS. A new δ-FeOOH supported nano-Au catalyst was prepared by a facile method using HAuCl 4 as the gold source and NaBH 4 as the reducing agent. The samples (denoted as AuNPs/FeOOH) were characterized by means of X-ray diffraction (XRD), UV-vis and infrared spectroscopies and scanning electron microscope (SEM). The obtained characterization data confirmed the formation of Au nanoparticles on the δ-FeOOH matrix surface. SEM observations showed that Au nanoparticles have a spherical morphology and good dispersion with a narrow size distribution on the surface of iron (III) oxyhydroxide. The catalyst exhibits significantly high catalytic activity for hydrogenation of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) at room temperature. The high performance obtained can be attributed to the specific characteristics of the nanostructure of the catalyst of nano-Au deposited on the external surface of δ-FeOOH, including plenty of oxygen-containing groups of δ-FeOOH for anchoring AuNPs. Moreover, the catalytic activity increased when the AuNPs content in the δ-FeOOH support. The AuNPs-based δ-FeOOH hybrids are interesting catalysts for hydrogenation of nitrophenols to aminophenols.

Au–ZnO prepared by simple in situ reduction and spontaneous of gold nanoparticles on the surface of the layered zinc hydroxide using a novel one-pot method

Materials Chemistry and Physics, 2015

Abstract This work reports on a reproducible and simple approach to the synthesis of nanocomposit... more Abstract This work reports on a reproducible and simple approach to the synthesis of nanocomposites based on gold metal nanoparticles (AuNPs) and layered compounds. Layered zinc hydroxide (ZHL-layered), a layered inorganic material, was used as host for the deposition of the gold nanoparticles. It was demonstrated that gold nanoparticles were rapidly formed when ZHL-layered was added to the ethanol chloroauric acid solution at room temperature. In this system, the ethyl alcohol acted as a solvent of the gold precursor and as a reducing agent, where the Au (III) ions were mainly reduced via redox reaction between the metallic precursor and the solvent. Measurements from gas chromatography/mass spectrometry showed that the AuNPs are produced with the formation of acetaldehyde. X-ray powder diffraction (XRD) indicated that the AuNPs were adsorbed on the surface of the ZHL-layered support. The structural, morphologic and optical properties of the nanocomposites based on AuNPs and ZHL-layered (Au-ZHL) were also investigated. According to UV–vis spectroscopy and transmission electron microscopy (TEM), the resulting nanoparticles were homogeneous, spherically shaped and highly stable with no aggregation dispersed in the ZHL-layered. This simple method indicates that Au (III) ions can be easily reduced, without the use of external reducing agents, in the presence of ZHL-layered and ethyl alcohol. Finally, we also demonstrated that Au-ZHL nanocomposites can be employed as templates for the preparation of zinc oxide decorated with AuNPs (hereafter named as Au–ZnO) using phase transformation at lower temperatures.

Durante este período de dois anos que se passaram de mestrado, agradeço primeiramente a Deus que ... more Durante este período de dois anos que se passaram de mestrado, agradeço primeiramente a Deus que me sustentou e que com certeza estava ao meu lado em tempos difíceis. Agradeço minha mãe e meu pai (in memorian), Maria Gomes Germino e Carlos Roberto Germino, que sempre deram apoio e incentivo a todas minhas escolhas. Agradeço minha orientadora e professora, Teresa Dib Zambon Atvars, pela oportunidade de ter realizado o mestrado, pelas discussões, pela confiança, pela ajuda em momentos difíceis, pela compreensão, etc., e rumo ao doutorado.

CCDC 1842335: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

The Journal of Physical Chemistry C, 2020

Zn(II) coordination compounds with asymmetric salicylidene ligands in poly[9,9-dioctylfluorenyl-2... more Zn(II) coordination compounds with asymmetric salicylidene ligands in poly[9,9-dioctylfluorenyl-2,7-diyl] (PFO) composites were used for all-solution-processable white organic light-emitting diode (WOLED) purposes. These Zn(II) complexes were strategically synthesized to optimize their electronic structures, starting from the widespread known salophen core. Vertical excitation energies and natural transition orbital (NTO) densities of Zn(salicylidenes) were evaluated using density functional theory/time-dependent density functional theory (DFT/TD-DFT) at the PBE0/6−311++G(d,p) level of theory, presenting good accuracy to their experimental optical properties. Diodes were assembled with Zn(salicylidenes) dispersed into a PFOconducting polymer matrix at 0.1, 0.5, 1.0, and 2.5 % mol•mol-1 with the architecture: ITO|PEDOT:PSS|PVK|PFO:Zn(salicylidene)|Ca|Al. The electrical properties of the diodes are dependent on the relative concentration of the coordination compounds in the polymer matrix, where an optimized performance was obtained using diluted samples. The modified Zn(salophen) derivatives (II and III) also presented greater performance compared to the precursor Zn(salophen) (I). In addition, interesting color tunability was obtained depending on the device composition, and for Zn(BTS) with 0.1 and 0.5%, we obtained coordinated color emission very similar to white (0.27, 0.36) and (0.29, 0.41), respectively. The observed color was a composition of the polymeric blue emission and green emission from the coordination compounds. The discussion of the efficiency was based on the determination of the carrier mobilities using the trap-charge limited current (TCLC) model. According to these values, the best performance of the diodes with Zn(BTS) is due to a pronounced increase of the charge mobility compared to the polymer itself and other coordination compounds.

The Journal of Physical Chemistry C, 2020

Two derivatives salicylidene-4,6-(dimethylamino)pyridine (KM1) and salicylidene-5-bromo-4,6-(dime... more Two derivatives salicylidene-4,6-(dimethylamino)pyridine (KM1) and salicylidene-5-bromo-4,6-(dimethylamino)pyridine (KM2) reactive to excited-state intramolecular proton transfer (ESIPT) were synthesized as a strategy to produce white light diodes with small organic molecules. White color resulted from the presence of both normal (420 nm) and tautomeric (550− 580 nm) species emission. The photophysical features of N* and T* were unveiled in solution and the solid state. The ESIPT mechanism revealed the influence of near attack conformation (NAC), and the relevance intramolecular hydrogen bonding (IMHB) further evaluated by 1 H NMR. Organic Light-emitting Diodes (OLEDs) were ensembled as Al/Ca/PVK:X/PE-DOT:PSS/ITO/glass where X = KM1 or KM2 (0.3% mol mol −1) using solution-processed protocols. KM1 or KM2 was solubilized in poly(9-vinylcarbazole), PVK, and the device of KM2 produced a chromaticity of (0.32, 0.27) according to the Commission Internationale de L'Eclairage (CIE) 1931 scale, which is slightly violet. The same device using KM1 reached CIE (0.33, 0.34), which is considered extremely close to pure white.

Advanced Optical Materials, 2020

2D metal halide semiconductors have been intensively studied in the past few years due to their u... more 2D metal halide semiconductors have been intensively studied in the past few years due to their unique optical properties and potential for new‐generation photonic devices. Despite the large number of recent works, this class of materials is still in need of further understanding due to their complex structural and optical characteristics. In this work, a molecular‐level explanation for the dual band emission in the 2D (C4H9NH3)2PbI4 in its bulk form is presented, demonstrating that this feature is caused by a strong exciton–phonon coupling. Temperature‐dependent photoluminescence with Raman and IR spectroscopies reveals that vibrations involving the C‐NH3+ butylammonium polar head are responsible for this exciton–phonon coupling. Additionally, experimental shifts in the mean phonon frequencies coupled with the electronic excitation, combined with a theoretical model, show that these vibrational modes present a soft‐mode behavior in the phase transition of this material.

Many multication perovskites for highly stable and efficient solar cells benefit from rubidium io... more Many multication perovskites for highly stable and efficient solar cells benefit from rubidium iodide introduced in the precursor solution. It is well known that Rb + influences positively the optoelectronic and mobility properties and has a direct effect upon crystallization and halide homogenization. As Rb + is often incorporated by adding RbI in the precursor solution, it can be difficult to distinguish the influence of Rb + and Iseparately. Herein, we report a post-passivation of methylammonium-free (CsFA) perovskite films with rubidium butyrate (RbBu). The passivation with RbBu increases the hydrophobicity of the perovskite surface and passivates shallow and deep traps, leading to an increase of chargecarrier lifetimes and diffusion lengths. Consequently, a better photovoltaic performance is also observed. These superior properties are attributed to both surface (halide-vacancy) and grain-boundary passivation by the carboxylate group and Rb + , respectively. We found that Rb + itself acts as a direct and powerful passivating agent for multication perovskites, and this is proven by decoupling its contribuition and halide's contribuition to other important performance parameters (e.g. crystallization, halide vacancies filling, etc).

Disentangling X‐Ray and Sunlight Irradiation Effects Under a Controllable Atmosphere in Metal Halide Perovskites

Solar RRL

Metal halide perovskites are versatile materials for photovoltaic and optoelectronic applications... more Metal halide perovskites are versatile materials for photovoltaic and optoelectronic applications owing to their adjustable bandgap and emission properties. Nevertheless, a drawback is their photo‐structural–chemical instability. Herein, structural and optical responses of metal halide perovskite films, exploiting in situ X‐ray and visible light stimuli under dry and humid atmospheres, are correlated. It shows that the interplay of the physical parameters responsible for sample evolution depends in a nontrivial way on the nature of the excitation, radiation power density, and moisture conditions. Two perovskite samples demonstrate the relevance of each composition. They are resilient under a dry atmosphere, but the presence of water or oxygen molecules in the ambient air leads to structural and optical changes under irradiation. However, the sample reaction depends on the photons’ excitation energy and power density to be effective. Under a dry atmosphere, the halide segregation inv...

Journal of the Brazilian Chemical Society

Sustainable energy generation has been a growing concern worldwide due to the alarming effects of... more Sustainable energy generation has been a growing concern worldwide due to the alarming effects of climate changes in the last few decades. In this scenario, perovskite solar cells hold great promise in contributing for a greener global energy matrix. Despite the great potential of this technology, several difficulties to deploy perovskite solar panels are yet to be overcome, being their long-term stability one of the most critical. In this sense, this work offers an alternative to improve the long-term, operational stability of the devices by passivating the CsFAMA perovskite active layer with a mixture of N-(2-aminoethyl)naphthalimide and mercaptopropionic acid. These modifications improved the perovskite and device stability under ambient conditions. The solar cells without encapsulation and with post-treatment with 5 mM modifier solution retained ca. 90% of its initial power conversion efficiency (PCE) after 500 h exposed to ambient conditions, while standard solar cells retained...

Light-induced halide segregation in perovskites with wrinkled morphology

Journal of Energy Chemistry

New strategies for the improvement of the photo and electroluminescent properties of Zn(II) and Pt(II) Salicylidenes

Color tunable hybrid light-emitting diodes based on perovskite quantum dot/conjugated polymer

Inorganic organic metal halide perovskite materials have been investigated for several technologi... more Inorganic organic metal halide perovskite materials have been investigated for several technological applications, such as photovoltaic cells, lasers, photodetectors and light emitting diodes (LEDs), either in the bulk form or as colloidal nanoparticles. Recently, all inorganic Cesium Lead Halide (CsPbX3, X=Cl,Br, I) perovskite quantum dots (PQDs) were reported with high photoluminescence quantum yield with narrow emission lines in the visible wavelengths. Here, green-emitting perovskite quantum dots (PQDs) prepared by a synthetic method based on a mixture of oleylamine and oleic acid as surfactants were applied in the electroluminescent layer of hybrid LEDs in combination with two different conjugated polymers: polyvinylcarbazole (PVK) or poly(9,9-di-n-octylfluorenyl-2,7-diyl) (PFO). The performance of the diodes and the emission color tuning upon dispersion of different concentrations of the PQDs in the polymer matrix is discussed. The presented approach aims at the combination of...

Effect of the Zn coordination complex on the excited-state and two-photon absorption spectra of a novel sallicylidene compound

Developing solid state NIR emitters and simultaneously discriminative detection trace water in or... more Developing solid state NIR emitters and simultaneously discriminative detection trace water in organic solvents has long been a significant challenge. In this work, a novel diketopyrrolopyrrole-based luminogen (DPP1) with excited state intramolecular proton transfer (ESIPT) and aggregation-induced emission (AIE) characteristics has been designed and synthesized. Its amorphous and crystal solids show red and NIR-emissive fluorescence at 625 nm and 675 nm, respectively. When DPP1 reacted with fluoride anion, the resulting system (DPP1.F) can discriminatively detect water content in aprotic solvents with colorimetric and fluorescent dual-modes. Distinct fluorescent responses of "turn on", "ratiometric turn off", "ratiometric turn on" and low limit of detection of 0.0064 v%, 0.042 v% and 0.192 v% in THF, acetone, and acetonitrile were obtained, respectively. The water-induced sensitive and fast change in THF was applied to the determination of water in foodstuffs in practical solid-state indicator paper strips.

Journal of Materials Chemistry C, 2021

Correction for ‘Reduced graphene oxide in perovskite solar cells: the influence on film formation... more Correction for ‘Reduced graphene oxide in perovskite solar cells: the influence on film formation, photophysics, performance, and stability’ by Paulo Ernesto Marchezi et al., J. Mater. Chem. C, 2021, DOI: 10.1039/D1TC01360B.

Journal of Luminescence, 2021

′-bipyridylene)vinylene-alt-2,5-(1,4-bis(octyloxy)vinylene)] (PBPyVOctV), was synthesized by the ... more ′-bipyridylene)vinylene-alt-2,5-(1,4-bis(octyloxy)vinylene)] (PBPyVOctV), was synthesized by the polymerization of 5,5 ′-divinyl-2,2 ′-bipyridine with 1,4-dibromo-2,5-bis(octyloxy) benzene through a Heck cross-coupling reaction. Then, a metallopolymer, PBPyVOctV-Eu(tta) 3 , was obtained by the bipyridine chelating coordination of PBPyVOctV with europium (Eu(III)) complex, Eu(tta) 3 .xH 2 O (where tta is 2thenoyltrifluoroacetonate). The incorporation of an europium center into the polymer backbone changed the optical and electronic properties of the conjugated polymer. The photoluminescence of the materials and electroluminescence properties of solution-processed organic light-emitting diodes (OLEDs) consisting of composites of PVK as a host with PBPyVOctV, Eu(tta) 3 .xH 2 O or PBPyVOctV-Eu(tta) 3 as guests were studied. The diode containing PVK:PBPyVOctV-Eu(tta) 3 as emissive layer delivered the highest luminance and highest current efficiency, with an orange color emission, as a result of combined emissions from the europium ions and polymer structure.

Angewandte Chemie International Edition, 2020

Angabe der unten stehenden Digitalobjekt-Identifizierungsnummer (DOI) zitiert werden. Die deutsch... more Angabe der unten stehenden Digitalobjekt-Identifizierungsnummer (DOI) zitiert werden. Die deutsche Übersetzung wird gemeinsam mit der endgültigen englischen Fassung erscheinen. Die endgültige englische Fassung (Version of Record) wird ehestmöglich nach dem Redigieren und einem Korrekturgang als Early-View-Beitrag erscheinen und kann sich naturgemäß von der AA-Fassung unterscheiden. Leser sollten daher die endgültige Fassung, sobald sie veröffentlicht ist, verwenden. Für die AA-Fassung trägt der Autor die alleinige Verantwortung.

Materials Research, 2019

Carbon dots (C-dots) possess the attractive properties of high stability, low toxicity, good wate... more Carbon dots (C-dots) possess the attractive properties of high stability, low toxicity, good water solubility, simple synthetic routes as well as size and excitation-dependent photoluminescence (PL).The aim of this work was to synthesize photoluminescent C-dots by hydrothermal method using acerola fruit (Malpighiaemarginata) as a row material, since this fruit contains large number of organic molecules. Studies about the optimal synthesis conditions were performed, where these organic molecules were converted into C-dots by hydrothermal carbonization at 180 ºC for 18 h. The C-dots exhibited a green emission light at 459 nm when excited under UV-light (λ ex = 370 nm). These nanomaterials were also successfully used to prepare C-dots/poly (vinyl alcohol) luminescent composites (C-dots/PVA). Both C-dots and C-dots/PVA composite films were investigated by using colorimetric visual sensor for Fe 3+ metal ions detection. The results show that the prepared C-dots and C-dots/poly presented strong green emission light. The emission spectra of above materials were quenched in the presence of Fe 3+ ions. Thus, highly specific "turn off" fluorescence sensing of Fe 3+ was achieved using fluorescent C-dots. Regarding, this work describe that the polymeric films as sensors of metallic ions in aqueous solution appears as a new perspectives to design new composite materials.

Journal of Luminescence, 2018

The photo-and electroluminescent properties of a copolymer containing fluorene, terpyridine and c... more The photo-and electroluminescent properties of a copolymer containing fluorene, terpyridine and complexed sites with trivalent europium ions (LaPPS66Eu) was 2 investigated. The non-complexed backbone (LaPPS66) and an analogous chemical structure of the ligand/Eu 3+ site (LaPPS66M) as a model compound were used for comparison and interpretation of the photophysical properties. Experiments were carried out using PVK as a dispersive matrix either in a blend form or in a bilayer configuration. Absorption and emission spectra, time-resolved emission spectra (TRES) and Förster Resonance Energy Transfer efficiency () were used to account for the differences found for the photophysical properties of each configuration.

Química Nova, 2017

NEW HYBRIDS BASED ON IRON (III) OXYHYDROXIDE AND GOLD NANOPARTICLES (AuNPs / FeOOH) as CATALYSTS ... more NEW HYBRIDS BASED ON IRON (III) OXYHYDROXIDE AND GOLD NANOPARTICLES (AuNPs / FeOOH) as CATALYSTS FOR THE REDUCTION OF ORGANIC ENVIRONMENTAL POLLUTANTS. A new δ-FeOOH supported nano-Au catalyst was prepared by a facile method using HAuCl 4 as the gold source and NaBH 4 as the reducing agent. The samples (denoted as AuNPs/FeOOH) were characterized by means of X-ray diffraction (XRD), UV-vis and infrared spectroscopies and scanning electron microscope (SEM). The obtained characterization data confirmed the formation of Au nanoparticles on the δ-FeOOH matrix surface. SEM observations showed that Au nanoparticles have a spherical morphology and good dispersion with a narrow size distribution on the surface of iron (III) oxyhydroxide. The catalyst exhibits significantly high catalytic activity for hydrogenation of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) at room temperature. The high performance obtained can be attributed to the specific characteristics of the nanostructure of the catalyst of nano-Au deposited on the external surface of δ-FeOOH, including plenty of oxygen-containing groups of δ-FeOOH for anchoring AuNPs. Moreover, the catalytic activity increased when the AuNPs content in the δ-FeOOH support. The AuNPs-based δ-FeOOH hybrids are interesting catalysts for hydrogenation of nitrophenols to aminophenols.

Au–ZnO prepared by simple in situ reduction and spontaneous of gold nanoparticles on the surface of the layered zinc hydroxide using a novel one-pot method

Materials Chemistry and Physics, 2015

Abstract This work reports on a reproducible and simple approach to the synthesis of nanocomposit... more Abstract This work reports on a reproducible and simple approach to the synthesis of nanocomposites based on gold metal nanoparticles (AuNPs) and layered compounds. Layered zinc hydroxide (ZHL-layered), a layered inorganic material, was used as host for the deposition of the gold nanoparticles. It was demonstrated that gold nanoparticles were rapidly formed when ZHL-layered was added to the ethanol chloroauric acid solution at room temperature. In this system, the ethyl alcohol acted as a solvent of the gold precursor and as a reducing agent, where the Au (III) ions were mainly reduced via redox reaction between the metallic precursor and the solvent. Measurements from gas chromatography/mass spectrometry showed that the AuNPs are produced with the formation of acetaldehyde. X-ray powder diffraction (XRD) indicated that the AuNPs were adsorbed on the surface of the ZHL-layered support. The structural, morphologic and optical properties of the nanocomposites based on AuNPs and ZHL-layered (Au-ZHL) were also investigated. According to UV–vis spectroscopy and transmission electron microscopy (TEM), the resulting nanoparticles were homogeneous, spherically shaped and highly stable with no aggregation dispersed in the ZHL-layered. This simple method indicates that Au (III) ions can be easily reduced, without the use of external reducing agents, in the presence of ZHL-layered and ethyl alcohol. Finally, we also demonstrated that Au-ZHL nanocomposites can be employed as templates for the preparation of zinc oxide decorated with AuNPs (hereafter named as Au–ZnO) using phase transformation at lower temperatures.

Durante este período de dois anos que se passaram de mestrado, agradeço primeiramente a Deus que ... more Durante este período de dois anos que se passaram de mestrado, agradeço primeiramente a Deus que me sustentou e que com certeza estava ao meu lado em tempos difíceis. Agradeço minha mãe e meu pai (in memorian), Maria Gomes Germino e Carlos Roberto Germino, que sempre deram apoio e incentivo a todas minhas escolhas. Agradeço minha orientadora e professora, Teresa Dib Zambon Atvars, pela oportunidade de ter realizado o mestrado, pelas discussões, pela confiança, pela ajuda em momentos difíceis, pela compreensão, etc., e rumo ao doutorado.

CCDC 1842335: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

The Journal of Physical Chemistry C, 2020

Zn(II) coordination compounds with asymmetric salicylidene ligands in poly[9,9-dioctylfluorenyl-2... more Zn(II) coordination compounds with asymmetric salicylidene ligands in poly[9,9-dioctylfluorenyl-2,7-diyl] (PFO) composites were used for all-solution-processable white organic light-emitting diode (WOLED) purposes. These Zn(II) complexes were strategically synthesized to optimize their electronic structures, starting from the widespread known salophen core. Vertical excitation energies and natural transition orbital (NTO) densities of Zn(salicylidenes) were evaluated using density functional theory/time-dependent density functional theory (DFT/TD-DFT) at the PBE0/6−311++G(d,p) level of theory, presenting good accuracy to their experimental optical properties. Diodes were assembled with Zn(salicylidenes) dispersed into a PFOconducting polymer matrix at 0.1, 0.5, 1.0, and 2.5 % mol•mol-1 with the architecture: ITO|PEDOT:PSS|PVK|PFO:Zn(salicylidene)|Ca|Al. The electrical properties of the diodes are dependent on the relative concentration of the coordination compounds in the polymer matrix, where an optimized performance was obtained using diluted samples. The modified Zn(salophen) derivatives (II and III) also presented greater performance compared to the precursor Zn(salophen) (I). In addition, interesting color tunability was obtained depending on the device composition, and for Zn(BTS) with 0.1 and 0.5%, we obtained coordinated color emission very similar to white (0.27, 0.36) and (0.29, 0.41), respectively. The observed color was a composition of the polymeric blue emission and green emission from the coordination compounds. The discussion of the efficiency was based on the determination of the carrier mobilities using the trap-charge limited current (TCLC) model. According to these values, the best performance of the diodes with Zn(BTS) is due to a pronounced increase of the charge mobility compared to the polymer itself and other coordination compounds.

The Journal of Physical Chemistry C, 2020

Two derivatives salicylidene-4,6-(dimethylamino)pyridine (KM1) and salicylidene-5-bromo-4,6-(dime... more Two derivatives salicylidene-4,6-(dimethylamino)pyridine (KM1) and salicylidene-5-bromo-4,6-(dimethylamino)pyridine (KM2) reactive to excited-state intramolecular proton transfer (ESIPT) were synthesized as a strategy to produce white light diodes with small organic molecules. White color resulted from the presence of both normal (420 nm) and tautomeric (550− 580 nm) species emission. The photophysical features of N* and T* were unveiled in solution and the solid state. The ESIPT mechanism revealed the influence of near attack conformation (NAC), and the relevance intramolecular hydrogen bonding (IMHB) further evaluated by 1 H NMR. Organic Light-emitting Diodes (OLEDs) were ensembled as Al/Ca/PVK:X/PE-DOT:PSS/ITO/glass where X = KM1 or KM2 (0.3% mol mol −1) using solution-processed protocols. KM1 or KM2 was solubilized in poly(9-vinylcarbazole), PVK, and the device of KM2 produced a chromaticity of (0.32, 0.27) according to the Commission Internationale de L'Eclairage (CIE) 1931 scale, which is slightly violet. The same device using KM1 reached CIE (0.33, 0.34), which is considered extremely close to pure white.

Advanced Optical Materials, 2020

2D metal halide semiconductors have been intensively studied in the past few years due to their u... more 2D metal halide semiconductors have been intensively studied in the past few years due to their unique optical properties and potential for new‐generation photonic devices. Despite the large number of recent works, this class of materials is still in need of further understanding due to their complex structural and optical characteristics. In this work, a molecular‐level explanation for the dual band emission in the 2D (C4H9NH3)2PbI4 in its bulk form is presented, demonstrating that this feature is caused by a strong exciton–phonon coupling. Temperature‐dependent photoluminescence with Raman and IR spectroscopies reveals that vibrations involving the C‐NH3+ butylammonium polar head are responsible for this exciton–phonon coupling. Additionally, experimental shifts in the mean phonon frequencies coupled with the electronic excitation, combined with a theoretical model, show that these vibrational modes present a soft‐mode behavior in the phase transition of this material.

Many multication perovskites for highly stable and efficient solar cells benefit from rubidium io... more Many multication perovskites for highly stable and efficient solar cells benefit from rubidium iodide introduced in the precursor solution. It is well known that Rb + influences positively the optoelectronic and mobility properties and has a direct effect upon crystallization and halide homogenization. As Rb + is often incorporated by adding RbI in the precursor solution, it can be difficult to distinguish the influence of Rb + and Iseparately. Herein, we report a post-passivation of methylammonium-free (CsFA) perovskite films with rubidium butyrate (RbBu). The passivation with RbBu increases the hydrophobicity of the perovskite surface and passivates shallow and deep traps, leading to an increase of chargecarrier lifetimes and diffusion lengths. Consequently, a better photovoltaic performance is also observed. These superior properties are attributed to both surface (halide-vacancy) and grain-boundary passivation by the carboxylate group and Rb + , respectively. We found that Rb + itself acts as a direct and powerful passivating agent for multication perovskites, and this is proven by decoupling its contribuition and halide's contribuition to other important performance parameters (e.g. crystallization, halide vacancies filling, etc).