Luminescent properties and lattice defects correlation on zinc oxide

The ZnO luminescent properties are strongly influenced by the preparation method and they are principally related to electronic and crystalline structures. This work reports about the correlation among luminescence properties of ZnO, obtained from zinc hydroxycarbonate, and crystalline lattice defects, microstrain, as function of thermal treatment. The crystallite size increase and the qualitative microstrain, obtained by Williamson-Hall plots, decrease as function of temperature. The evolution of electronic defects is analyzed by luminescence spectroscopy based on energy of the electronic transitions. From excitation spectrum, it is verified two bands around 377 nm and 405 nm attributed to the transitions between valence-conduction bands and valence band to interstitial zinc level, respectively. The emission spectra of sample treated at 600 degreesC shows large band at 670 nm. However, the green emission around 530 nm is observed for samples treated at 900 degreesC. The intensities of excitation and emission bands are associated with the increase of the electronic defects that depend on the strain lattice decrease. The lowest strain lattice results on the best green luminescent properties of zinc oxide. (C) 2001 Elsevier B.V. Ltd. All rights reserved.

Luminescent properties of some rare earth phosphates

Luminescent properties of scandium and yttrium phosphates are discussed and mechanisms involving their emissions proposed.

Local Er(III) environment in luminescent titanosilicates prepared from microporous precursors

The local environment of Er3+ ions in microporous titanosilicate ETS-10 and in synthetic narsarsukite and glassy materials obtained by calcination of ETS-10 has been investigated by EXAFS, Raman and photoluminescence spectroscopies. Er L-III-edge EXAFS studies of Er3+-doped ETS-10 support the view that the exchanged Er3+ ions reside close to the (negatively charged) TiO6 octahedra. In ETS-10, Er3+ is partially bonded to framework oxygen atoms and hydration water molecules. The Er...Ti distance (3.3 Angstrom) is similar to the Na...Ti distances (3.15-3.20 Angstrom) reported previously for Na-ETS-10. Although the exact location of the ErO6 units within the host structure of Er3+-doped synthetic narsarsukite is still an open question, it is most likely that Er3+ substitutes Ti4+ rather than Na+ ions. EXAFS spectroscopy indicates that no significant clustering of erbium atoms occurs in the titanosilicate samples studied. Evidence for the insertion of Er3+ ions in the framework of narsarsukite has been obtained by Raman spectroscopy. This is indicated by the increasing full-width at half-maximum (FWHM) of the 775 cm(-1) peak and the increasing intensity of the anatase peaks as the erbium content increases. In addition, as the narsarsukite Er3+ content increases a band at ca. 515 cm(-1) firstly broadens and subsequently a new peak appears at ca. 507 cm(-1).Er3+-doped narsarsukite exhibits a characteristic local vibrational frequency, (h) over bar omega ca. 330 cm(-1), with an electron-phonon coupling, g ca. 0.2, which constitutes additional evidence for framework Er3+ insertion. The number of lines in the infrared emission spectrum of synthetic narsarsukite indicates the presence of two optically-active erbium centres with very similar local environments and an average I-4(13/2) lifetime of 7.8 +/- 0.2 ms.

Synthesis and thermal characterization of luminescent powers of terbium(III) with mixed ligands

This work deals with the synthesis and thermal decomposition of complexes of general formula: Ln(beta-dik)(3)L (where Ln=Tb(+3), beta-dik=4,4,4-trifluoro-1-phenyl-1,3butanedione(btfa) and L=1,10-fenantroline(phen) or 2,2-bipiridine(bipy). The powders were characterized by melting point, FTIR spectroscopy, LTV-visible, elemental analysis, scanning differential calorimeter(DSC) and thermogravimetry(TG). The TG/DSC curves were obtained simultaneously in a system DSC-TGA, under nitrogen atmosphere. The experimental conditions were: 0.83 ml.s(-1) carrier gas flow, 2.0 +/- 0.5 mg samples and 10 degrees C.min(-1) heating rate. The CHN elemental analysis of the Tb(btfa)(3)bipy and Tb(btfa)(3)phen complexes, are in good agreement with the expected values. The IR spectra evinced that the metal ion is coordinated to the ligands via C=O and C-N groups. The TG/DTG/DSC curves of the complexes show that they decompose before melting. The profiles of the thermal decomposition of the Tb(btfa)3phen and Tb(btfa)3bipy showed six and five decomposition stages, respectively. Our data suggests that the thermal stability of the complexes under investigation followed the order: Tb(btfa)(3)phen < Tb(btfa)(3)bipy.

Nanoscale manipulation of CdSe quantum dots in layer-by-layer films: influence of the host polyelectrolyte on the luminescent properties

Thioglycolic acid-capped Use quantum dots (QDs) were assembled on glass substrates with two distinct polyelectrolytes, viz poly(allylamine hydrochloride) (PAH) and poly(amidoamine) (PAMAM), generation 4 dendrimer, via the layer-by-layer (LbL) technique. Films containing up to 30 polyelectrolyte/QD bilayers were prepared. The growth of the multilayers was monitored with UV-vis spectroscopy, which showed an almost linear increase in the absorbance of the 2.8 nm QDs at 535 nm with the number of deposited bilayers. AFM measurements estimated a film thickness of 3 nm per bilayer for the PAH/Cdse films. The adsorption process and the optical properties of the PAMAM/CdSe LbL films were further analyzed layer-by-layer using surface plasmon resonance (SPR), from which a thickness of 3.2 nm was found for a PAMAM/CdSe bilayer. Photoluminescence measurements revealed higher photooxidation of the quantum dots in PAH/CdSe than in PAMAM/CdSe films. (c) 2004 Elsevier B.V. All rights reserved.

Structure of luminescent mono and di-urethanesil nanocomposites doped with Eu3+ ions

A structure modeling of two families of sol-gel derived Eu3+-doped organic/inorganic hybrids based on the results of small-angle X-ray scattering experiments is reported. The materials are composed of poly(oxyethylene) chains grafted at one or both ends to siloxane groups and are called mono- and di-urethanesils, respectively. A theoretical function corresponding to a two-level hierarchical structure model fits well the experimental Scattering curves. The first level corresponds to small siloxane clusters embedded in a polymeric matrix. The secondary level is associated to the existence of siloxane cluster rich domains surrounded by a cluster-depleted polymeric matrix. Results show that increasing europium doping favors the growth of the secondary domains. (C) 2002 Elsevier B.V. B.V. All rights reserved.

Morphological and luminescent studies on nanosized Er, Yb-Yttrium oxide up-converter prepared from different precursors

In this paper, we report luminescent and morphological studies with yttrium oxide samples doped with ytterbium and erbium. The samples were prepared by the combustion method and also from different precursors: oxalate, basic carbonate and polymeric resin. All powders were identified Lis being an yttrium oxide with a C-form structure, independent of the employed precursor. From mean crystallite size measurements, it was verified that oxides prepared through the polymeric precursor and combustion methods lead to the smallest crystallite size. Particle shape and size were investigated by SEM and TEM, and showed that both the oxalate precursor and the combustion methods do not provide oxide materials of suitable shape or size, on the other hand. The basic carbonate and polymeric precursors resulted in spherically shaped particles with an average diameter of 90 and 15 run. respectively, Upon 980 run diode laser excitation, green and red emission lines were detected for all samples and were assigned to the H-2(11/2) S-4(3/2) -> I-4(15/2) and (4)Fg(9/2) -> 4I(15/12) transitions, respectively. Such transitions are characteristic for Er3+ and result from energy transfer from Yb3+ energy levels, F-2(7/2) -> F-2(5/2). A relationship between the decrease in the mean crystallite size and the enhancement in red emission was also established as well as the influence of the presence of a high percentage of Yb-3 Both factors promote ET from Yb3+ (F-2(5/2)) to Er3+ (I-4(11/2)). (c) 2004 Elsevier B.V. All rights reserved.

Nanostructure and luminescent properties of sol-gel derived europium-doped amine functionalised hybrids

The effect of doping by europium triflate on the nanoscopic structure of organic-inorganic hybrid formed by a siliceous network containing pendant amine-terminated propyl chains, called aminosils, was investigated by Small-Angle X-ray Scattering (SAXS). It appears that the composites exhibit a two-level structure. The first level consists of well-condensed cubic-like siloxane octamers, with a radius of gyration around 2 angstrom. The second level is formed by the aggregation of these siloxane nanodomains to form larger structures, in which the nanodomains are spatially correlated and separated by the organic pendant chains. Europium doping inhibits the aggregation between siloxane octamers, leading to a less compact second-level structure. This can be explained by the Eu3+ stop coordination close to the external surface of the siloxane nanodomains, as detected by luminescence spectroscopy.

Luminescent properties of yttrium diphenylphosphinate activated by europium

The synthesis and spectroscopic characterization of yttrium diphenylphosphinates doped with europium are reported. The purity of all samples was confirmed by carbon and hydrogen micro analysis, thermal analysis, IR vibrational spectroscopy, and X-ray diffraction. Luminescence spectra indicated the presence of two or more symmetry centers. The dynamic luminescence measurements suggested that one symmetry site presented an inversion center, while the others had lower symmetry. The average quantum yield of Eu3+ emission in the yttrium, matrices was 60%. (c) 2005 Elsevier B.V. All rights reserved.

Study of the annealing temperature effect on the structural and luminescent properties of SrWO4:Eu phosphors prepared by a non-hydrolytic sol-gel process

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Non-leachable highly luminescent ordered mesoporous SiO2 spherical particles

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Luminescent nano-composites generated from a spray

The spray-pyrolysis (SP) synthesis technique has been employed to obtain SiO2:Eu3+ and gamma-AlOOH:Eu3+, It was possible to obtain sub-micrometric spherical particles of SiO2 with luminescent Eu3+ ions bonded to the silica surface or embedded in amorphous silica beads, by controlling the synthesis and annealing process. Boehmite y-AlOOH doped with Eu3+ nanoparticles were synthesized by SP at moderate temperature (200 degrees C) with Eu3+ ions bonded to the surface hydroxyls of the boehmite nanocrystals. Luminescent nanocomposites were obtained by controlled reaction of gamma-AlOOH:Eu3+ nanocrystals with ASN (asparagine). In these nano-composites, the Eu3+ are held at the surface of the boehmite nanocrystals and partially shielded from interactions with additional luminescence quenchers (hydroxyl groups, water molecules). (C) 2008 Elsevier B.V. All rights reserved.

Structural and Spectroscopic Properties of Luminescent Er3+-Doped SiO2-Ta2O5 Nanocomposites

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Synthesis of a functionalized europium complex and deposition of luminescent Langmuir-Blodgett (LB) films

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Syntheses and luminescent properties of tetrahedral nickel(0) complexes

Tetrahedral nickel(0) complexes [NiL4], [Ni(dppe)2] and [Ni(CO)2(SbPh3)2] (L=AsPh3, SbPh3, P(OPh)3, dppe=1,2-bis(diphenylphosphino)ethane) were prepared by reduction of NiCl2·6H2O with NaBH4 under N2 or CO atmosphere in the presence of the ligand. The complex [Ni(SbPh3)4] was also obtained by electrolysis at -1.3 V (Ag/Ag+), under a platinum gauze, of the system NiCl2·6H2O/SbPh3 (molar ratio=1:4). These complexes, both in the solid state and in solution, show an orange emission at room temperature, when excited with UV radiation. A qualitative molecular orbital diagram for the [NiL4] complexes is proposed. Electronic absorption spectra of the complexes show bands near 400 nm assigned as MLCT π*2e←d2t2. A 1A1←3T1 transition is suggested for the emission observed in these systems. Lifetimes in microsecond range were estimated from time-resolved emission spectra. Spectroscopic properties of the free ligands have also been investigated.