Claudia Felinto - Academia.edu (original) (raw)

Papers by Claudia Felinto

Research paper thumbnail of Microwave-Assisted Preparation of Luminescent Inorganic Materials: A Fast Route to Light Conversion and Storage Phosphors

Molecules

Luminescent inorganic materials are used in several technological applications such as light-emit... more Luminescent inorganic materials are used in several technological applications such as light-emitting displays, white LEDs for illumination, bioimaging, and photodynamic therapy. Usually, inorganic phosphors (e.g., complex oxides, silicates) need high temperatures and, in some cases, specific atmospheres to be formed or to obtain a homogeneous composition. Low ionic diffusion and high melting points of the precursors lead to long processing times in these solid-state syntheses with a cost in energy consumption when conventional heating methods are applied. Microwave-assisted synthesis relies on selective, volumetric heating attributed to the electromagnetic radiation interaction with the matter. The microwave heating allows for rapid heating rates and small temperature gradients yielding homogeneous, well-formed materials swiftly. Luminescent inorganic materials can benefit significantly from the microwave-assisted synthesis for high homogeneity, diverse morphology, and rapid screen...

Research paper thumbnail of Luminescent hybrid materials functionalized with lanthanide ethylenodiaminotetraacetate complexes containing β-diketonate as antenna ligands

Journal of Luminescence, 2015

ABSTRACT Three organic–inorganic hybrid materials based on silica gel functionalized with (3-amin... more ABSTRACT Three organic–inorganic hybrid materials based on silica gel functionalized with (3-aminopropyl)tri-methoxysilane (APTS), [3-(2-aminoetilamino)-propil]-trimetoxissilano (DAPTS) and 3-[2-(2-aminoetila-mino)etilamino] propiltrimetoxysilane (TAPTS) and subsequently modified with EDTA derivative were prepared by nonhomogeneous route and were then characterized. The resulting materials named SilXN-EDTA (X¼1 for APTS, 2 for DAPTS and 3 for TAPTS) were used to obtain new lanthanide Ln 3 þ-β-diketonate (Ln 3 þ ¼Eu 3 þ , Gd 3 þ and Tb 3 þ) complexes covalently linked to the functionalized silica gel surfaces (named SilXN-EDTALn-dik, dik ¼tta, dbm, bzac and acac). The photophysical properties of the new luminescent materials were investigated and compared with those with similar system presenting water molecules coordinated to the lanthanide ions, SilXN-EDTALn-H 2 O. The SilXN-EDTAEu-dik and SilXN-EDTATb-dik systems displayed characteristic red and green luminescence when excited by UV radiation. Furthermore, the quantitative results showed that the emission quantum efficiency (η), experimental intensity parameters Ω 2 and Ω 4 , and Einstein's emission coefficient (A 0J) of the SilXN-EDTAEu-dik materials were largely dependent on the ligands. Based on the luminescence data, the most efficient intramolecular energy transfer processes were found to the SilXN-EDTAEu-dik (dik: tta and dbm) and SilXN-EDTATb-acac materials, which exhibited more pure emission colors. These materials are promising red and green phosphors, respectively.

Research paper thumbnail of Modeling intramolecular energy transfer in lanthanide chelates: A critical review and recent advances

Research paper thumbnail of Synthesis, Structure Study, First-Principles Investigations and Luminescence Properties of Europium and Terbium Complexes

Research paper thumbnail of Luminescence properties of the Ln–EDTA complexes covalently linked to the chitosan biopolymers containing β‐diketonate as antenna ligands

Research paper thumbnail of Development of highly luminescent PMMA films doped with Eu3+β-diketonate coordinated on ancillary ligand

Journal of Materials Science: Materials in Electronics

In this work, [Eu(tta)3(4-picNO)2] and [Eu(dbm)3(4-picNO)] complexes were incorporated on differe... more In this work, [Eu(tta)3(4-picNO)2] and [Eu(dbm)3(4-picNO)] complexes were incorporated on different concentrations (x = 1, 3, 5, 10 and 15%) in PMMA polymeric matrix (4-picNO: 4-Methylpyridine N-oxide) by the solvent casting method, yielding transparent and highly luminescent polymeric films. These materials were analyzed by X-ray diffraction, scanning electron microscopy and by energy dispersive, ultraviolet–visible spectroscopy, luminescence and vacuum ultraviolet–ultraviolet spectroscopies. The luminescence spectra of doped PMMA films are in agreement with an efficient intramolecular diketonate (tta) ligand-to-europium energy transfer. Furthermore, the values of experimental intensity parameters (Ω2,4) for luminescent polymeric materials were quite similar to those ones for isolated complexes, indicating that there is a homogeneous dispersion of Eu3+ complexes in the polymeric matrix, preserving their chemical and structural features. These behavior were also observed from the CIE diagram that show great similarity between the (x,y) coordinates for the doped PMMA samples compared to the isolated β-diketonate complexes with a reddish color tuning. The photostability investigation of the doped PMMA polymeric films and Eu3+ complexes has been also reported.

Research paper thumbnail of Persistent luminescence of inorganic nanophosphors prepared by wet-chemical synthesis

Journal of Alloys and Compounds

The synthesis of efficient nanosized persistent luminescence materials remains a challenge for th... more The synthesis of efficient nanosized persistent luminescence materials remains a challenge for the community. Paradoxically, due to the dependence of the point lattice defects and the persistent luminescence efficiency, the control of the defect formation, favorable when the materials are prepared at high temperatures, normally leads to particle growth and sintering. In this work, efficient nanosized rare earth doped disilicates Sr2MgSi2O7:Eu2+,Dy3+ were synthesized via three different wet-chemical methods taking advantages of the microwave-assisted reduction process as a support step to produce high-quality polycrystalline materials. The crystallite size of the sample showed to be smaller when the decomposition temperature of the precursors is higher and close to the phase formation energy. The excitation VUV spectroscopy indicated that despite being nanocrystalline, the materials optical band gap has just a small difference compared one to another. The reduction of Eu3+ to Eu2+ was successfully obtained, since the f-d interconfigurational transitions of Eu2+ 4f65d1→4f7 emission were observed in the blue region of the spectra. The persistent luminescence efficiency measured through its lasting decay time was close to the commercial materials references and with the advantage of having size control during the synthesis method that can lead to the size dependent applications of photonic materials.

Research paper thumbnail of Photoluminescence of single-phased white light emission materials based on simultaneous Tb3+, Eu3+ and Dy3+ doping in CaWO4 matrix

Journal of Alloys and Compounds

Research paper thumbnail of Mechanoluminescence of Coordination Compounds

Research paper thumbnail of Preparation and photoluminescence properties of functionalized silica materials incorporating europium complexes

Optical Materials, Aug 1, 2011

Research paper thumbnail of Optical investigation of Y 2 O 3 : Sm 3 + nanophosphor prepared by combustion and Pechini methods

J Luminesc, 2007

ABSTRACT Nanoparticles of trivalent samarium ion doped into yttrium oxide with attractive photolu... more ABSTRACT Nanoparticles of trivalent samarium ion doped into yttrium oxide with attractive photoluminescent properties were prepared using combustion and Pechini methods treated at low heating temperatures. Combustion technique focused on an exothermic reaction between metal nitrates and glycine as fuel leading to the desired product where Y2O3:Sm3+ nanophosphor was heated at 400, 500 and . For Pechini method, which is based upon in situ polyesterification between citric acid and ethylene glycol, the phosphor material was treated only at . The powders were characterized by X-ray diffraction, infrared absorption spectroscopy and scanning electronic microscopy. Photoluminescent study of Y2O3:Sm3+ system showed the characteristic emission narrow lines containing (J+1/2)-manifolds of intraconfigurational transitions ( and ) of Sm3+ ion with the transition as a prominent intensity, when excitation was monitored at 406 nm . The luminescence decay curves suggest a mono-exponential behavior.

Research paper thumbnail of Comparison of Column Chromatographic and Precipitation Methods for the Purification of a Macrocyclic Polyether Extractant

Http Dx Doi Org 10 1081 Ss 100100814, Feb 15, 2007

ABSTRACT Column chromatography on aminopropyl-derivatized silica and precipitation of a complex w... more ABSTRACT Column chromatography on aminopropyl-derivatized silica and precipitation of a complex with perchloric acid have been evaluated as methods for the purification of di-tert-butylcyclohexano-18-crown-6 (DtBuCH18C6), a compound frequently employed for the selective extraction of strontium from acidic nitrate media. Both methods are shown to provide a simple and effective means of eliminating inactive sample components (i.e., impurities or stereoisomers incapable of extracting strontium) from the crown ether and enriching the material in 4(z),4′(z) cis-syn-cis DtBuCH18C6, a stereoisomer capable of highly efficient strontium extraction.

Research paper thumbnail of Synthesis and luminescent properties of supramolecules of β-diketonate of Eu(III) and crown ethers as ligands

This work reports the synthesis and luminescence behavior of the diaquatris(thenoyltrifluoraceton... more This work reports the synthesis and luminescence behavior of the diaquatris(thenoyltrifluoracetonate)europium(III) with dibenzo18-crown-6 (DB18C6) and 18-crown-6 (18C6), in the solid state. The new compounds Eu(TTA) 3 (H 2 O) 2 (DB18C6) 2 and Eu(TTA) 3 (H 2 O) 2 (18C6) 2 were characterized by elemental analysis, infrared spectroscopy, thermalanalysis and scattering electronic microscopy. The emission spectra show narrow emission bands that arise from the 5 D 0-7 F J transitions (J ¼ 024) of the Eu 3+ ion. The spectral data of the Eu(TTA) 3 (H 2 O) 2 (DB18C6) 2 and Eu(TTA) 3 (H 2 O) 2 (18C6) 2 compounds present, respectively, one and two peaks assigned to the 5 D 0-7 F 0 transition (B578 nm), suggesting one and two sites of symmetry around the metal ion. In addition, the luminescence decay curves of these DB18C6 and 18C6 systems were better fitted by a mono-and bi-exponential decays, respectively. The values of the experimental intensity parameters (O l) indicate that the europium ion in the complexes is in a highly polarizable chemical environment. The values of emission quantum efficiencies for the two Eu(III)-supramolecular compounds are similar (Z ¼ 26%).

Research paper thumbnail of Influence of titanium and lutetium on the persistent luminescence of ZrO_2

Optical Materials Express, 2012

Non-doped as well as titanium and lutetium doped zirconia (ZrO 2) materials were synthesized via ... more Non-doped as well as titanium and lutetium doped zirconia (ZrO 2) materials were synthesized via the sol-gel method and structurally characterized with X-ray powder diffraction. The addition of Ti in the zirconia lattice does not change the crystalline structure whilst the Lu doping introduces a small fraction of the tetragonal phase. The UV excitation results in a bright white-blue luminescence at ca. 500 nm for all the materials which emission could be assigned to the Ti 3+ e g  t 2g transition. The persistent luminescence originates from the same Ti 3+ center. The thermoluminescence data shows a well-defined though rather similar defect structures for all the zirconia materials. The kinetics of persistent luminescence was probed with the isothermal decay curve analyses which indicated significant retrapping. The short duration of persistent luminescence was attributed to the quasi-continuum distribution of the traps and to the possibility of shallow traps even below the room temperature.

Research paper thumbnail of Standard molar enthalpies of formation of Y2O3, Ho2O3, and Er2O3 at the temperature 298.15 K

The Journal of Chemical Thermodynamics, 1993

Abstract Samples of Y 2 O 3, Ho 2 O 3, and Er 2 O 3 that were crystalline, but dissolved relative... more Abstract Samples of Y 2 O 3, Ho 2 O 3, and Er 2 O 3 that were crystalline, but dissolved relatively rapidly, were synthesized by careful decomposition of the corresponding nitrates. Enthalpies of solution of high-purity samples of Y 2 O 3, and Er 2 O 3 were measured in ...

Research paper thumbnail of Comparison of Column Chromatographic and Precipitation Methods for the Purification of a Macrocyclic Polyether Extractant

Separation Science and Technology, 1999

Column chromatography on aminopropyl-derivatized silica and precipitation of a complex with perch... more Column chromatography on aminopropyl-derivatized silica and precipitation of a complex with perchloric acid have been evaluated as methods for the purification of di-tert-butylcyclohexano-18-crown-6 (DtBuCH18C6), a compound frequently employed for the ...

Research paper thumbnail of Synthesis and luminescent properties of Eu3+-complexes with 2-acyl-1,3-indandionates (ACIND) and TPPO ligands: The first X-ray structure of Eu–ACIND complex

Polyhedron, 2006

Europium complexes presenting general formulas [Eu(ACIND) 3 (H 2 O) 2 ] and [Eu(ACIND) 3 (TPPO) 2... more Europium complexes presenting general formulas [Eu(ACIND) 3 (H 2 O) 2 ] and [Eu(ACIND) 3 (TPPO) 2 ] have been synthesized and characterized. In these formulas ACIND is stands for the ligands 2-acetyl-1,3-indandionate (AIND), 2-isovaleryl-1,3-indandionate (ISOV-IND) or 2-benzyl-1,3-indandionate (BIND). The [Eu(ISOVIND) 3 (H 2 O)(EtOH)] complex was also prepared and its structure determined by single crystal X-ray analysis, showing that this complex crystallize in a monoclinic space group P2 1 /n with the water molecules bridging through the hydrogen bond. The Eu(III) ion is eight-coordinate in a bicapped trigonal prismatic geometry defined by the oxygen donor atoms with a site of symmetry close to C 2m. Isovaleryl groups in the ISOVIND molecules in the structure are disordered over two positions of the europium complex. Carbon atoms in ethanol molecule are disordered by the thermal vibration. Photoluminescence properties of these complexes in solid state were investigated both experimentally and theoretically, suggesting an efficient ligandto-metal intramolecular energy transfer process.

Research paper thumbnail of Luminescent nanoparticles of MgAl2O4:Eu,Dy prepared by citrate sol–gel method

Optical Materials, 2008

MgAl 2 O 4 :Eu, Dy nanoparticles were prepared by citrate sol-gel method and thermally treated at... more MgAl 2 O 4 :Eu, Dy nanoparticles were prepared by citrate sol-gel method and thermally treated at 600, 700, 800 and 900°C. The trivalent europium ion is partially reduced to the divalent state at 700 and 800°C. Infrared spectra of the phosphors showed bands around 700 and 520 cm À1 corresponding to the AlO 6 groups. X-ray diffraction patterns present sharp reflections of samples heated from 700 to 900°C indicating the MgAl 2 O 4 spinel phase. Grain size in the range 20-30 nm were observed by measurement of transmission electron microscopy (TEM). The emission spectra of the phosphors show a broadened band at 480 nm assigned to the 4f 6 5d ? 4f 7 (8 S 7/2) transition of Eu 2+ ion overlapped to the 4 F 9/2 ? 6 H 15/2 transition of the Dy 3+ ion. Besides, the 4 F 9/2 ? 6 H 13/2 transition (579 nm) of Dy 3+ ion is overlapped with the 5 D 0 ? 7 F 0 (578 nm) and 5 D 0 ? 7 F 1 (595 nm) transitions from the Eu 3+ ion. Excitation spectra of the sample heated at 900°C monitoring the excitation at 615 nm of 5 D 0 ? 7 F 2 transition of Eu 3+ ion exhibit a broad band assigned to the O ? Eu 3+ ligand-to-metal charge-transfer states (LMCT) around 280 nm. The samples present green persistent luminescence after exposure to UV radiation. The chromaticity coordinates were obtained from the luminescence emission spectrum.

Research paper thumbnail of Photoluminescence behavior of the Sm3+ and Tb3+ ions doped into the Gd2(WO4)3 matrix prepared by the Pechini and ceramic methods

Journal of the Brazilian Chemical Society, 2004

Os compostos Gd 2 (WO 4) 3 :RE 3+ (onde RE = Sm e Tb) preparados via métodos Pechini e cerâmico f... more Os compostos Gd 2 (WO 4) 3 :RE 3+ (onde RE = Sm e Tb) preparados via métodos Pechini e cerâmico foram caracterizados por difratometria de raios-X e espectroscopia de absorção na região do infravermelho. Estes materiais de terras raras apresentam alta intensidade luminescente, laranja para os compostos de Sm 3+ e verde para os de Tb 3+ , quando excitados com radiação UV. Os espectros de excitação dos compostos mostraram bandas largas oriundas da transferência de carga ligante-metal (O→W e O→RE 3+) e bandas estreitas associadas às transições intraconfiguracionais (4f-4f). Os espectros de excitação do sistema com Tb 3+ também exibiram bandas largas atribuídas à transição interconfiguracional (4f-5d). Quando os espectros de emissão dos compostos contendo Sm 3+ e Tb 3+ são obtidos com excitação no íon observa-se somente transições finas 4 G 5/2 → 6 H J (J = 5/2, 7/2, 9/2 e 11/2) e 5 D 4 → 7 F J (J = 0-6). Por outro lado, quando a excitação é monitorada na banda de transferência de carga (BTC, 270 nm) são também observadas bandas largas atribuídas a BTC (O→W). Os parâmetros de intensidade experimentais, η Sm e η Eu , apresentaram comportamentos similares, sugerindo que o íon Sm 3+ encontra-se em um ambiente químico altamente polarizável e que o caráter covalente da interação metal-ligante é semelhante àquele do sistema tungstato de európio. O processo de relaxação cruzada baseado nos níveis 5 D 3 e 5 D 4 do sistema Gd 2 (WO 4) 3 :Tb 3 foi reportado. The Gd 2 (WO 4) 3 :RE 3+ compounds (where RE 3+ = Sm and Tb) were prepared by the Pechini and ceramic methods and characterized by X-ray diffraction and infrared spectroscopy. These rare earth materials present high orange (Sm 3+-compound) and green (Tb 3+-compound) luminescence intensity under UV radiation. The excitation spectra of these compounds presented broad bands arising from ligand-to-metal charge transfer (O→W and O→RE 3+) and narrow bands from 4f-intraconfigurational transitions. The excitation spectra of Tb 3+ system also exhibit broad bands attributed to the interconfigurational transition (4f-5d). The emission spectra exhibited the 4 G 5/2 → 6 H J (J = 5/2, 7/2, 9/2 and 11/2) and 5 D 4 → 7 F J (J = 0-6) transitions (direct excitation), for the systems doped with Sm 3+ and Tb 3+ , respectively, while a broad band assigned to the LMCT (O→W) is observed when the excitation is monitored on the O→W LMCT state around 270 nm. The experimental intensity parameters η Sm and η Eu present similar behaviors, suggesting that the Sm 3+ ion is in a highly polarizable chemical environment with similar covalent character of the metal-donor atom interaction to the tungstate doped europium system. The cross-relaxation process from the 5 D 3 to the 5 D 4 levels of the Gd 2 (WO 4) 3 :Tb 3+ system has been also reported.

Research paper thumbnail of Energy Transfer Processes in Tb(III)-Dibenzoylmethanate Complexes with Phosphine Oxide Ligands

Journal of the Brazilian Chemical Society, 2013

Este trabalho relata a síntese, a caracterização e as propriedades luminescentes dos complexos de... more Este trabalho relata a síntese, a caracterização e as propriedades luminescentes dos complexos de fórmulas [Tb(DBM) 3 L], [Tb(DBM) 2 (NO 3)L 2)] e [Tb(DBM)(NO 3) 2 (HMPA) 2)] (DBM = dibenzoilmetanato; L: TPPO = óxido de trifenilfosfina ou HMPA = óxido de hexametilfosforamida). Os compostos foram caracterizados por análise elementar (CHN), titulação complexométrica com EDTA e espectroscopia no infravermelho com transformada de Fourier (FTIR), e as propriedades de fotoluminescência foram avaliadas. As energias dos estados tripletos do ligante DBM foram determinadas experimentalmente a partir dos espectros de fosforescência resolvidos no tempo dos compostos análogos do íon Gd 3+. As energias aumentam em função do número de ânions nitratos que substituem o ligante DBM nos complexos. Ademais, os espectros de luminescência e os tempos de vida dos níveis emissores revelaram que a eficiência de transferência de energia ligante-metal segue a mesma tendência. Ao contrário dos complexos tris-DBM, o bis-e o mono-DBM apresentaram elevada intensidade de luminescência, sendo candidatos promissores para camadas emissoras de luz em dispositivos moleculares conversores de luz (LCMD). The Tb 3+-b-diketonate complexes [Tb(DBM) 3 L], [Tb(DBM) 2 (NO 3)L 2 ] and [Tb(DBM)(NO 3) 2 (HMPA) 2 ] (DBM = dibenzoylmethanate; L: TPPO = triphenylphosphine oxide or HMPA = hexamethylphosphine oxide) were prepared and characterized by elemental analysis (CHN), complexometric titration with EDTA and Fourier transform infrared (FTIR) spectroscopy, and the photoluminescence properties evaluated. The triplet state energies of the coordinated DBM ligands were determined using time-resolved phosphorescence spectra of analogous Gd 3+ complexes. The results show that the energies increase along with the number of coordinated nitrate anions replacing the DBM ligand in the complexes. The luminescence spectra and emission lifetime measurements revealed that the ligand-to-metal energy transfer efficiency follows the same tendency. Unlike the tris-DBM complexes, bis-and mono-DBM presented high luminescence, and may act as promising candidates for preparation of the emitting layer of light converting molecular devices (LCMDs).

Research paper thumbnail of Microwave-Assisted Preparation of Luminescent Inorganic Materials: A Fast Route to Light Conversion and Storage Phosphors

Molecules

Luminescent inorganic materials are used in several technological applications such as light-emit... more Luminescent inorganic materials are used in several technological applications such as light-emitting displays, white LEDs for illumination, bioimaging, and photodynamic therapy. Usually, inorganic phosphors (e.g., complex oxides, silicates) need high temperatures and, in some cases, specific atmospheres to be formed or to obtain a homogeneous composition. Low ionic diffusion and high melting points of the precursors lead to long processing times in these solid-state syntheses with a cost in energy consumption when conventional heating methods are applied. Microwave-assisted synthesis relies on selective, volumetric heating attributed to the electromagnetic radiation interaction with the matter. The microwave heating allows for rapid heating rates and small temperature gradients yielding homogeneous, well-formed materials swiftly. Luminescent inorganic materials can benefit significantly from the microwave-assisted synthesis for high homogeneity, diverse morphology, and rapid screen...

Research paper thumbnail of Luminescent hybrid materials functionalized with lanthanide ethylenodiaminotetraacetate complexes containing β-diketonate as antenna ligands

Journal of Luminescence, 2015

ABSTRACT Three organic–inorganic hybrid materials based on silica gel functionalized with (3-amin... more ABSTRACT Three organic–inorganic hybrid materials based on silica gel functionalized with (3-aminopropyl)tri-methoxysilane (APTS), [3-(2-aminoetilamino)-propil]-trimetoxissilano (DAPTS) and 3-[2-(2-aminoetila-mino)etilamino] propiltrimetoxysilane (TAPTS) and subsequently modified with EDTA derivative were prepared by nonhomogeneous route and were then characterized. The resulting materials named SilXN-EDTA (X¼1 for APTS, 2 for DAPTS and 3 for TAPTS) were used to obtain new lanthanide Ln 3 þ-β-diketonate (Ln 3 þ ¼Eu 3 þ , Gd 3 þ and Tb 3 þ) complexes covalently linked to the functionalized silica gel surfaces (named SilXN-EDTALn-dik, dik ¼tta, dbm, bzac and acac). The photophysical properties of the new luminescent materials were investigated and compared with those with similar system presenting water molecules coordinated to the lanthanide ions, SilXN-EDTALn-H 2 O. The SilXN-EDTAEu-dik and SilXN-EDTATb-dik systems displayed characteristic red and green luminescence when excited by UV radiation. Furthermore, the quantitative results showed that the emission quantum efficiency (η), experimental intensity parameters Ω 2 and Ω 4 , and Einstein's emission coefficient (A 0J) of the SilXN-EDTAEu-dik materials were largely dependent on the ligands. Based on the luminescence data, the most efficient intramolecular energy transfer processes were found to the SilXN-EDTAEu-dik (dik: tta and dbm) and SilXN-EDTATb-acac materials, which exhibited more pure emission colors. These materials are promising red and green phosphors, respectively.

Research paper thumbnail of Modeling intramolecular energy transfer in lanthanide chelates: A critical review and recent advances

Research paper thumbnail of Synthesis, Structure Study, First-Principles Investigations and Luminescence Properties of Europium and Terbium Complexes

Research paper thumbnail of Luminescence properties of the Ln–EDTA complexes covalently linked to the chitosan biopolymers containing β‐diketonate as antenna ligands

Research paper thumbnail of Development of highly luminescent PMMA films doped with Eu3+β-diketonate coordinated on ancillary ligand

Journal of Materials Science: Materials in Electronics

In this work, [Eu(tta)3(4-picNO)2] and [Eu(dbm)3(4-picNO)] complexes were incorporated on differe... more In this work, [Eu(tta)3(4-picNO)2] and [Eu(dbm)3(4-picNO)] complexes were incorporated on different concentrations (x = 1, 3, 5, 10 and 15%) in PMMA polymeric matrix (4-picNO: 4-Methylpyridine N-oxide) by the solvent casting method, yielding transparent and highly luminescent polymeric films. These materials were analyzed by X-ray diffraction, scanning electron microscopy and by energy dispersive, ultraviolet–visible spectroscopy, luminescence and vacuum ultraviolet–ultraviolet spectroscopies. The luminescence spectra of doped PMMA films are in agreement with an efficient intramolecular diketonate (tta) ligand-to-europium energy transfer. Furthermore, the values of experimental intensity parameters (Ω2,4) for luminescent polymeric materials were quite similar to those ones for isolated complexes, indicating that there is a homogeneous dispersion of Eu3+ complexes in the polymeric matrix, preserving their chemical and structural features. These behavior were also observed from the CIE diagram that show great similarity between the (x,y) coordinates for the doped PMMA samples compared to the isolated β-diketonate complexes with a reddish color tuning. The photostability investigation of the doped PMMA polymeric films and Eu3+ complexes has been also reported.

Research paper thumbnail of Persistent luminescence of inorganic nanophosphors prepared by wet-chemical synthesis

Journal of Alloys and Compounds

The synthesis of efficient nanosized persistent luminescence materials remains a challenge for th... more The synthesis of efficient nanosized persistent luminescence materials remains a challenge for the community. Paradoxically, due to the dependence of the point lattice defects and the persistent luminescence efficiency, the control of the defect formation, favorable when the materials are prepared at high temperatures, normally leads to particle growth and sintering. In this work, efficient nanosized rare earth doped disilicates Sr2MgSi2O7:Eu2+,Dy3+ were synthesized via three different wet-chemical methods taking advantages of the microwave-assisted reduction process as a support step to produce high-quality polycrystalline materials. The crystallite size of the sample showed to be smaller when the decomposition temperature of the precursors is higher and close to the phase formation energy. The excitation VUV spectroscopy indicated that despite being nanocrystalline, the materials optical band gap has just a small difference compared one to another. The reduction of Eu3+ to Eu2+ was successfully obtained, since the f-d interconfigurational transitions of Eu2+ 4f65d1→4f7 emission were observed in the blue region of the spectra. The persistent luminescence efficiency measured through its lasting decay time was close to the commercial materials references and with the advantage of having size control during the synthesis method that can lead to the size dependent applications of photonic materials.

Research paper thumbnail of Photoluminescence of single-phased white light emission materials based on simultaneous Tb3+, Eu3+ and Dy3+ doping in CaWO4 matrix

Journal of Alloys and Compounds

Research paper thumbnail of Mechanoluminescence of Coordination Compounds

Research paper thumbnail of Preparation and photoluminescence properties of functionalized silica materials incorporating europium complexes

Optical Materials, Aug 1, 2011

Research paper thumbnail of Optical investigation of Y 2 O 3 : Sm 3 + nanophosphor prepared by combustion and Pechini methods

J Luminesc, 2007

ABSTRACT Nanoparticles of trivalent samarium ion doped into yttrium oxide with attractive photolu... more ABSTRACT Nanoparticles of trivalent samarium ion doped into yttrium oxide with attractive photoluminescent properties were prepared using combustion and Pechini methods treated at low heating temperatures. Combustion technique focused on an exothermic reaction between metal nitrates and glycine as fuel leading to the desired product where Y2O3:Sm3+ nanophosphor was heated at 400, 500 and . For Pechini method, which is based upon in situ polyesterification between citric acid and ethylene glycol, the phosphor material was treated only at . The powders were characterized by X-ray diffraction, infrared absorption spectroscopy and scanning electronic microscopy. Photoluminescent study of Y2O3:Sm3+ system showed the characteristic emission narrow lines containing (J+1/2)-manifolds of intraconfigurational transitions ( and ) of Sm3+ ion with the transition as a prominent intensity, when excitation was monitored at 406 nm . The luminescence decay curves suggest a mono-exponential behavior.

Research paper thumbnail of Comparison of Column Chromatographic and Precipitation Methods for the Purification of a Macrocyclic Polyether Extractant

Http Dx Doi Org 10 1081 Ss 100100814, Feb 15, 2007

ABSTRACT Column chromatography on aminopropyl-derivatized silica and precipitation of a complex w... more ABSTRACT Column chromatography on aminopropyl-derivatized silica and precipitation of a complex with perchloric acid have been evaluated as methods for the purification of di-tert-butylcyclohexano-18-crown-6 (DtBuCH18C6), a compound frequently employed for the selective extraction of strontium from acidic nitrate media. Both methods are shown to provide a simple and effective means of eliminating inactive sample components (i.e., impurities or stereoisomers incapable of extracting strontium) from the crown ether and enriching the material in 4(z),4′(z) cis-syn-cis DtBuCH18C6, a stereoisomer capable of highly efficient strontium extraction.

Research paper thumbnail of Synthesis and luminescent properties of supramolecules of β-diketonate of Eu(III) and crown ethers as ligands

This work reports the synthesis and luminescence behavior of the diaquatris(thenoyltrifluoraceton... more This work reports the synthesis and luminescence behavior of the diaquatris(thenoyltrifluoracetonate)europium(III) with dibenzo18-crown-6 (DB18C6) and 18-crown-6 (18C6), in the solid state. The new compounds Eu(TTA) 3 (H 2 O) 2 (DB18C6) 2 and Eu(TTA) 3 (H 2 O) 2 (18C6) 2 were characterized by elemental analysis, infrared spectroscopy, thermalanalysis and scattering electronic microscopy. The emission spectra show narrow emission bands that arise from the 5 D 0-7 F J transitions (J ¼ 024) of the Eu 3+ ion. The spectral data of the Eu(TTA) 3 (H 2 O) 2 (DB18C6) 2 and Eu(TTA) 3 (H 2 O) 2 (18C6) 2 compounds present, respectively, one and two peaks assigned to the 5 D 0-7 F 0 transition (B578 nm), suggesting one and two sites of symmetry around the metal ion. In addition, the luminescence decay curves of these DB18C6 and 18C6 systems were better fitted by a mono-and bi-exponential decays, respectively. The values of the experimental intensity parameters (O l) indicate that the europium ion in the complexes is in a highly polarizable chemical environment. The values of emission quantum efficiencies for the two Eu(III)-supramolecular compounds are similar (Z ¼ 26%).

Research paper thumbnail of Influence of titanium and lutetium on the persistent luminescence of ZrO_2

Optical Materials Express, 2012

Non-doped as well as titanium and lutetium doped zirconia (ZrO 2) materials were synthesized via ... more Non-doped as well as titanium and lutetium doped zirconia (ZrO 2) materials were synthesized via the sol-gel method and structurally characterized with X-ray powder diffraction. The addition of Ti in the zirconia lattice does not change the crystalline structure whilst the Lu doping introduces a small fraction of the tetragonal phase. The UV excitation results in a bright white-blue luminescence at ca. 500 nm for all the materials which emission could be assigned to the Ti 3+ e g  t 2g transition. The persistent luminescence originates from the same Ti 3+ center. The thermoluminescence data shows a well-defined though rather similar defect structures for all the zirconia materials. The kinetics of persistent luminescence was probed with the isothermal decay curve analyses which indicated significant retrapping. The short duration of persistent luminescence was attributed to the quasi-continuum distribution of the traps and to the possibility of shallow traps even below the room temperature.

Research paper thumbnail of Standard molar enthalpies of formation of Y2O3, Ho2O3, and Er2O3 at the temperature 298.15 K

The Journal of Chemical Thermodynamics, 1993

Abstract Samples of Y 2 O 3, Ho 2 O 3, and Er 2 O 3 that were crystalline, but dissolved relative... more Abstract Samples of Y 2 O 3, Ho 2 O 3, and Er 2 O 3 that were crystalline, but dissolved relatively rapidly, were synthesized by careful decomposition of the corresponding nitrates. Enthalpies of solution of high-purity samples of Y 2 O 3, and Er 2 O 3 were measured in ...

Research paper thumbnail of Comparison of Column Chromatographic and Precipitation Methods for the Purification of a Macrocyclic Polyether Extractant

Separation Science and Technology, 1999

Column chromatography on aminopropyl-derivatized silica and precipitation of a complex with perch... more Column chromatography on aminopropyl-derivatized silica and precipitation of a complex with perchloric acid have been evaluated as methods for the purification of di-tert-butylcyclohexano-18-crown-6 (DtBuCH18C6), a compound frequently employed for the ...

Research paper thumbnail of Synthesis and luminescent properties of Eu3+-complexes with 2-acyl-1,3-indandionates (ACIND) and TPPO ligands: The first X-ray structure of Eu–ACIND complex

Polyhedron, 2006

Europium complexes presenting general formulas [Eu(ACIND) 3 (H 2 O) 2 ] and [Eu(ACIND) 3 (TPPO) 2... more Europium complexes presenting general formulas [Eu(ACIND) 3 (H 2 O) 2 ] and [Eu(ACIND) 3 (TPPO) 2 ] have been synthesized and characterized. In these formulas ACIND is stands for the ligands 2-acetyl-1,3-indandionate (AIND), 2-isovaleryl-1,3-indandionate (ISOV-IND) or 2-benzyl-1,3-indandionate (BIND). The [Eu(ISOVIND) 3 (H 2 O)(EtOH)] complex was also prepared and its structure determined by single crystal X-ray analysis, showing that this complex crystallize in a monoclinic space group P2 1 /n with the water molecules bridging through the hydrogen bond. The Eu(III) ion is eight-coordinate in a bicapped trigonal prismatic geometry defined by the oxygen donor atoms with a site of symmetry close to C 2m. Isovaleryl groups in the ISOVIND molecules in the structure are disordered over two positions of the europium complex. Carbon atoms in ethanol molecule are disordered by the thermal vibration. Photoluminescence properties of these complexes in solid state were investigated both experimentally and theoretically, suggesting an efficient ligandto-metal intramolecular energy transfer process.

Research paper thumbnail of Luminescent nanoparticles of MgAl2O4:Eu,Dy prepared by citrate sol–gel method

Optical Materials, 2008

MgAl 2 O 4 :Eu, Dy nanoparticles were prepared by citrate sol-gel method and thermally treated at... more MgAl 2 O 4 :Eu, Dy nanoparticles were prepared by citrate sol-gel method and thermally treated at 600, 700, 800 and 900°C. The trivalent europium ion is partially reduced to the divalent state at 700 and 800°C. Infrared spectra of the phosphors showed bands around 700 and 520 cm À1 corresponding to the AlO 6 groups. X-ray diffraction patterns present sharp reflections of samples heated from 700 to 900°C indicating the MgAl 2 O 4 spinel phase. Grain size in the range 20-30 nm were observed by measurement of transmission electron microscopy (TEM). The emission spectra of the phosphors show a broadened band at 480 nm assigned to the 4f 6 5d ? 4f 7 (8 S 7/2) transition of Eu 2+ ion overlapped to the 4 F 9/2 ? 6 H 15/2 transition of the Dy 3+ ion. Besides, the 4 F 9/2 ? 6 H 13/2 transition (579 nm) of Dy 3+ ion is overlapped with the 5 D 0 ? 7 F 0 (578 nm) and 5 D 0 ? 7 F 1 (595 nm) transitions from the Eu 3+ ion. Excitation spectra of the sample heated at 900°C monitoring the excitation at 615 nm of 5 D 0 ? 7 F 2 transition of Eu 3+ ion exhibit a broad band assigned to the O ? Eu 3+ ligand-to-metal charge-transfer states (LMCT) around 280 nm. The samples present green persistent luminescence after exposure to UV radiation. The chromaticity coordinates were obtained from the luminescence emission spectrum.

Research paper thumbnail of Photoluminescence behavior of the Sm3+ and Tb3+ ions doped into the Gd2(WO4)3 matrix prepared by the Pechini and ceramic methods

Journal of the Brazilian Chemical Society, 2004

Os compostos Gd 2 (WO 4) 3 :RE 3+ (onde RE = Sm e Tb) preparados via métodos Pechini e cerâmico f... more Os compostos Gd 2 (WO 4) 3 :RE 3+ (onde RE = Sm e Tb) preparados via métodos Pechini e cerâmico foram caracterizados por difratometria de raios-X e espectroscopia de absorção na região do infravermelho. Estes materiais de terras raras apresentam alta intensidade luminescente, laranja para os compostos de Sm 3+ e verde para os de Tb 3+ , quando excitados com radiação UV. Os espectros de excitação dos compostos mostraram bandas largas oriundas da transferência de carga ligante-metal (O→W e O→RE 3+) e bandas estreitas associadas às transições intraconfiguracionais (4f-4f). Os espectros de excitação do sistema com Tb 3+ também exibiram bandas largas atribuídas à transição interconfiguracional (4f-5d). Quando os espectros de emissão dos compostos contendo Sm 3+ e Tb 3+ são obtidos com excitação no íon observa-se somente transições finas 4 G 5/2 → 6 H J (J = 5/2, 7/2, 9/2 e 11/2) e 5 D 4 → 7 F J (J = 0-6). Por outro lado, quando a excitação é monitorada na banda de transferência de carga (BTC, 270 nm) são também observadas bandas largas atribuídas a BTC (O→W). Os parâmetros de intensidade experimentais, η Sm e η Eu , apresentaram comportamentos similares, sugerindo que o íon Sm 3+ encontra-se em um ambiente químico altamente polarizável e que o caráter covalente da interação metal-ligante é semelhante àquele do sistema tungstato de európio. O processo de relaxação cruzada baseado nos níveis 5 D 3 e 5 D 4 do sistema Gd 2 (WO 4) 3 :Tb 3 foi reportado. The Gd 2 (WO 4) 3 :RE 3+ compounds (where RE 3+ = Sm and Tb) were prepared by the Pechini and ceramic methods and characterized by X-ray diffraction and infrared spectroscopy. These rare earth materials present high orange (Sm 3+-compound) and green (Tb 3+-compound) luminescence intensity under UV radiation. The excitation spectra of these compounds presented broad bands arising from ligand-to-metal charge transfer (O→W and O→RE 3+) and narrow bands from 4f-intraconfigurational transitions. The excitation spectra of Tb 3+ system also exhibit broad bands attributed to the interconfigurational transition (4f-5d). The emission spectra exhibited the 4 G 5/2 → 6 H J (J = 5/2, 7/2, 9/2 and 11/2) and 5 D 4 → 7 F J (J = 0-6) transitions (direct excitation), for the systems doped with Sm 3+ and Tb 3+ , respectively, while a broad band assigned to the LMCT (O→W) is observed when the excitation is monitored on the O→W LMCT state around 270 nm. The experimental intensity parameters η Sm and η Eu present similar behaviors, suggesting that the Sm 3+ ion is in a highly polarizable chemical environment with similar covalent character of the metal-donor atom interaction to the tungstate doped europium system. The cross-relaxation process from the 5 D 3 to the 5 D 4 levels of the Gd 2 (WO 4) 3 :Tb 3+ system has been also reported.

Research paper thumbnail of Energy Transfer Processes in Tb(III)-Dibenzoylmethanate Complexes with Phosphine Oxide Ligands

Journal of the Brazilian Chemical Society, 2013

Este trabalho relata a síntese, a caracterização e as propriedades luminescentes dos complexos de... more Este trabalho relata a síntese, a caracterização e as propriedades luminescentes dos complexos de fórmulas [Tb(DBM) 3 L], [Tb(DBM) 2 (NO 3)L 2)] e [Tb(DBM)(NO 3) 2 (HMPA) 2)] (DBM = dibenzoilmetanato; L: TPPO = óxido de trifenilfosfina ou HMPA = óxido de hexametilfosforamida). Os compostos foram caracterizados por análise elementar (CHN), titulação complexométrica com EDTA e espectroscopia no infravermelho com transformada de Fourier (FTIR), e as propriedades de fotoluminescência foram avaliadas. As energias dos estados tripletos do ligante DBM foram determinadas experimentalmente a partir dos espectros de fosforescência resolvidos no tempo dos compostos análogos do íon Gd 3+. As energias aumentam em função do número de ânions nitratos que substituem o ligante DBM nos complexos. Ademais, os espectros de luminescência e os tempos de vida dos níveis emissores revelaram que a eficiência de transferência de energia ligante-metal segue a mesma tendência. Ao contrário dos complexos tris-DBM, o bis-e o mono-DBM apresentaram elevada intensidade de luminescência, sendo candidatos promissores para camadas emissoras de luz em dispositivos moleculares conversores de luz (LCMD). The Tb 3+-b-diketonate complexes [Tb(DBM) 3 L], [Tb(DBM) 2 (NO 3)L 2 ] and [Tb(DBM)(NO 3) 2 (HMPA) 2 ] (DBM = dibenzoylmethanate; L: TPPO = triphenylphosphine oxide or HMPA = hexamethylphosphine oxide) were prepared and characterized by elemental analysis (CHN), complexometric titration with EDTA and Fourier transform infrared (FTIR) spectroscopy, and the photoluminescence properties evaluated. The triplet state energies of the coordinated DBM ligands were determined using time-resolved phosphorescence spectra of analogous Gd 3+ complexes. The results show that the energies increase along with the number of coordinated nitrate anions replacing the DBM ligand in the complexes. The luminescence spectra and emission lifetime measurements revealed that the ligand-to-metal energy transfer efficiency follows the same tendency. Unlike the tris-DBM complexes, bis-and mono-DBM presented high luminescence, and may act as promising candidates for preparation of the emitting layer of light converting molecular devices (LCMDs).