Tb3+-> Eu3+ Energy Transfer in Mixed-Lanthanide-Organic Frameworks

In this work, we report a theoretical and experimental investigation of the energy transfer mechanism in two isotypical 2D coordination polymers, (infinity)[(Tb1-xEux)(DPA)(HDPA)], where H(2)DPA is pyridine 2,6-dicarboxylic acid and x = 0.05 or 0.50. Emission spectra of (infinity)[(Tb0.95Eu0.05)(DPA)(HDPA)] and (infinity)[(Tb0.5Eu0.5)(DPA)(HDPA)], (I) and (2), show that the high quenching effect on Tb3+ emission caused by Eu3+ ion indicates an efficient Tb3+-> Eu3+ energy transfer (ET). The k(ET) of Tb3+-> Eu3+ ET and rise rates (k(r)) of Eu3+ as a function of temperature for (1) are on the same order of magnitude, indicating that the sensitization of the Eu3+5D0 level is highly fed by ET from the D-5(4) level of Tb3+ ion. The eta(ET) and R-0 values vary in the 67-79% and 7.15 to 7.93 angstrom ranges. Hence, Tb3+ is enabled to transfer efficiently to Eu3+ that can occupy the possible sites at 6.32 and 6.75 angstrom. For (2), the ET processes occur on average with eta(ET) and R-0 of 97% and 31 angstrom, respectively. Consequently, Tb3+ ion is enabled to transfer energy to Eu3+ localized at different layers. The theoretical model developed by Malta was implemented aiming to insert more insights about the dominant mechanisms involved in the ET between lanthanides ions. Calculated single Tb3+-> Eu3+ ETs are three orders of magnitude inferior to those experimentally; however, it can be explained by the theoretical model that does not consider the role of phonon assistance in the Ln(3+)-> Ln(3+) ET processes. In addition, the Tb3+-> Eu3+ ET processes are predominantly governed by dipole-dipole (d-d) and dipole-quadrupole (d-q) mechanisms.

Near-infrared quantum cutting through a three-step energy transfer process in Nd3+-Yb3+ co-doped fluoroindogallate glasses

The Nd3+-Yb3+ couple was investigated in fluoroindogallate glasses using optical spectroscopy to elucidate the energy transfer mechanisms involved in the downconversion (DC) process. Upon excitation of a Nd3+ ion by an ultraviolet photon, DC through a three-step energy transfer process occurs, in which the energy of the ultraviolet photon absorbed by the Nd3+ ion is converted into three infrared photons emitted by Yb3+ ions, i.e. quantum cutting (QC). In addition, with excitation in the visible, our results confirm that the DC process occurs through a one-step energy transfer process, in which the energy of a visible photon absorbed by the Nd3+ ion is converted into only one infrared photon emitted by an Yb3+ ion. Time-resolved measurements enabled the estimation of the efficiencies of the cross-relaxation processes between Nd3+ and Yb3+ ions.

Measurement and model calculation of the temperature dependence of ligand-to-metal energy transfer rates in lanthanide complexes

Temperature dependent transient curves of excited levels of a model Eu3+ complex have been measured for the first time. A coincidence between the temperature dependent rise time of the 5D0 emitting level and decay time of the 5D1 excited level in the [Eu(tta)3(H2O)2] complex has been found, which unambiguously proves the T1→5D1→5D0 sensitization pathway. A theoretical approach for the temperature dependent energy transfer rates has been successfully applied to the rationalization of the experimental data.

A MODIS-Based Energy Balance to Estimate Evapotranspiration for Clear-Sky Days in Brazilian Tropical Savannas

Evapotranspiration (ET) plays an important role in global climate dynamics and in primary production of terrestrial ecosystems; it represents the mass and energy transfer from the land to atmosphere. Limitations to measuring ET at large scales using ground-based methods have motivated the development of satellite remote sensing techniques. The purpose of this work is to evaluate the accuracy of the SEBAL algorithm for estimating surface turbulent heat fluxes at regional scale, using 28 images from MODIS. SEBAL estimates are compared with eddy-covariance (EC) measurements and results from the hydrological model MGB-IPH. SEBAL instantaneous estimates of latent heat flux (LE) yielded r(2) = 0.64 and r(2) = 0.62 over sugarcane croplands and savannas when compared against in situ EC estimates. At the same sites, daily aggregated estimates of LE were r(2) = 0.76 and r(2) = 0.66, respectively. Energy balance closure showed that turbulent fluxes over sugarcane croplands were underestimated by 7% and 9% over savannas. Average daily ET from SEBAL is in close agreement with estimates from the hydrological model for an overlay of 38,100 km(2) (r(2) = 0.88). Inputs to which the algorithm is most sensitive are vegetation index (NDVI), gradient of temperature (dT) to compute sensible heat flux (H) and net radiation (Re). It was verified that SEBAL has a tendency to overestimate results both at local and regional scales probably because of low sensitivity to soil moisture and water stress. Nevertheless the results confirm the potential of the SEBAL algorithm, when used with MODIS images for estimating instantaneous LE and daily ET from large areas.

Dually fluorescent silica nanoparticles

The cationic dyes 9-aminoacridine (9AA) and safranine (Sf) were entrapped into silica spheres of about 0.2 mu m diameter prepared by modified Stober method. The fluorescent materials are investigated by steady-state and time-resolved emission, in addition of confocal fluorescence microscopy. Silica particles containing 9-aminoacridine (SP9AA) and safranine (SPSf or both dyes (SPSf9AA) are emissive particles. When both dyes are present in the same particle but loaded in sequential stages 9AA emission is quenched as a consequence of energy transfer from 9AA (donor) to Sf (acceptor). This result suggests that particle growing processes where the acceptor is incorporated first into the core do not prevent donor/acceptor pairs to be close due to an overlay of the concentration gradients of both dyes in a radial core-shell like distribution. (C) 2010 Elsevier B.V. All rights reserved.

Color tunability of intense upconversion emission from Er3+-Yb3+ co-doped SiO2-Ta2O5 glass ceramic planar waveguides

This work reports on the infrared-to-visible CW frequency upconversion from planar waveguides based on Er3+-Yb3+-doped 100-xSiO(2)-xTa(2)O(5) obtained by a sol-gel process and deposited onto a SiO2-Si substrate by dip-coating. Surface morphology and optical parameters of the planar waveguides were analyzed by atomic force microscopy and the m-line technique. The influence of the composition on the electronic properties of the glass-ceramic films was followed by the band gap ranging from 4.35 to 4.51 eV upon modification of the Ta2O5 content. Intense green and red emissions were detected from the upconversion process for all the samples after excitation at 980 nm. The relative intensities of the emission bands around 550 nm and 665 nm, assigned to the H-2(11/2) -> I-4(15/2), S-4(3/2) -> I-4(15/2), and F-4(9/2) -> I-4(15/2) transitions, depended on the tantalum oxide content and the power of the laser source at 980 nm. The upconversion dynamics were investigated as a function of the Ta2O5 content and the number of photons involved in each emission process. Based on the upconversion emission spectra and 1931CIE chromaticity diagram, it is shown that color can be tailored by composition and pump power. The glass ceramic films are attractive materials for application in upconversion lasers and near infrared-to-visible upconverters in solar cells.

Extracellular ATP triggers proteolysis and cytosolic Ca2+ rise in Plasmodium berghei and Plasmodium yoelii malaria parasites

Background: Plasmodium has a complex cell biology and it is essential to dissect the cell-signalling pathways underlying its survival within the host. Methods: Using the fluorescence resonance energy transfer (FRET) peptide substrate Abz-AIKFFARQ-EDDnp and Fluo4/AM, the effects of extracellular ATP on triggering proteolysis and Ca2+ signalling in Plasmodium berghei and Plasmodium yoelii malaria parasites were investigated. Results: The protease activity was blocked in the presence of the purinergic receptor blockers suramin (50 mu M) and PPADS (50 mu M) or the extracellular and intracellular calcium chelators EGTA (5 mM) and BAPTA/AM (25, 100, 200 and 500 mu M), respectively for P. yoelii and P. berghei. Addition of ATP (50, 70, 200 and 250 mu M) to isolated parasites previously loaded with Fluo4/AM in a Ca2+-containing medium led to an increase in cytosolic calcium. This rise was blocked by pre-incubating the parasites with either purinergic antagonists PPADS (50 mu M), TNP-ATP (50 mu M) or the purinergic blockers KN-62 (10 mu M) and Ip5I (10 mu M). Incubating P. berghei infected cells with KN-62 (200 mu M) resulted in a changed profile of merozoite surface protein 1 (MSP1) processing as revealed by western blot assays. Moreover incubating P. berghei for 17 h with KN-62 (10 mu M) led to an increase in rings forms (82% +/- 4, n = 11) and a decrease in trophozoite forms (18% +/- 4, n = 11). Conclusions: The data clearly show that purinergic signalling modulates P. berghei protease(s) activity and that MSP1 is one target in this pathway.

Persistent luminescence mechanisms: human imagination at work

The present status and future progress of the mechanisms of persistent luminescence are critically treated with the present knowledge. The advantages to be achieved by a further need as well as the pitfalls of the excessive use of imagination are shown. As usual, in the beginning of the present era of persistent luminescence since the mid 1990s, the imagination played a more important role than the sparse solid experimental data and the chemical common sense and knowledge was largely ignored. Since some five years, the mechanistic studies seem to have reached the maturity and - perhaps deceivingly - it seems that there are only details to be solved. However, the development of red emitting nanocrystalline materials poses a challenge also to the more fundamental studies and interpretation. The questions still luring in the darkness include the problems how the increased surface area affects the defect structure and how the "persistent energy transfer" really works. There is still some light to be thrown onto these matters starting with agreeing on the terminology: the term phosphorescence should be abandoned altogether. The long lifetime of persistent luminescence is due to trapping of excitation energy, not to the forbidden nature of the luminescent transition. However, the technically well-suited term "afterglow" should be retained for harmful, short persistent luminescence. (C) 2012 Optical Society of America

Plasmonic Coupling in Er3+:Au Tellurite Glass

In this paper, we report on luminescence and absorbance effects of Er+3:Au-doped tellurite glasses synthesized by a melting-quenching and heat treatment technique. After annealing times of 2.5, 5.0, 7.5, and 10.0 h, at 300 A degrees C, the gold nanoparticles (GNP) effects on the Er+3 are verified from luminescence spectra and the corresponding levels lifetime. The localized surface plasmon resonance around 800 nm produced a maximum fluorescence enhancement for the band ranging from 800 to 840 nm, corresponding to the transitions H-4(11/2) -> aEuro parts per thousand I-4(13/2) (805 nm) and S-4(3/2) -> aEuro parts per thousand I-4(13/2) (840 nm), with annealing time till 7.5 h. The measured lifetime of the levels H-4(11/2) and S-4(3/2) confirmed the lifetime reduction due to the energy transfer from the GNP to Er+3, causing an enhanced photon emission rate in these levels.

Novel europium and gadolinium complexes with methaneseleninate as ligand: Synthesis, characterization and spectroscopic study

The methaneseleninate and 1,10-phenanthroline were used as ligands in the synthesis of new lanthanide complexes. The photostability, emission quantum yield (q) and quantum efficiency (eta) of the D-5(0) emitting level of the Eu3+ ion were determined. An energy level diagram was used to establish the most relevant channels involved in the ligand-to-metal intramolecular energy transfer process. The nephelauxetic effect was investigated to assess the covalency of the ligand-metal chemical bond. The values of the experimental 4f-4f intensity parameters, suggest that this ion is in a chemical environment less polarisable than in the case of complexes with beta-diketonates as ligands. (C) 2011 Elsevier B.V. All rights reserved.

Photophysical properties of a fluorene-bipyridine copolymer and its complexes with europium

The synthesis and structural characterization of a europium complexed fluorene-bipyridine copolymer are described. A level of ion insertion of 80% in molar basis was achieved, and theoretical calculations showed that it required a twist of 179 degrees (49 kJ) between the pyridine units. Spectroscopy data showed that no electronic coupling between the main backbone and the complexation sites had occurred, but these hindered the interchain aggregation observed in the non complexed polymer. Preliminary electroluminescence studies showed that the EL and PL spectra are consistent, and that the ion had a trapping effect in the charge transport. (C) 2011 Elsevier B.V. All rights reserved.

Cytochrome c-promoted cardiolipin oxidation generates singlet molecular oxygen

The interaction of cytochrome c (cyt c) with cardiolipin (CL) induces protein conformational changes that favor peroxidase activity. This process has been correlated with CL oxidation and the induction of cell death. Here we report evidence demonstrating the generation of singlet molecular oxygen [O-2((1)Delta(g))] by a cyt c-CL complex in a model membrane containing CL. The formation of singlet oxygen was directly evidenced by luminescence measurements at 1270 nm and by chemical trapping experiments. Singlet oxygen generation required cyt c-CL binding and occurred at pH values higher than 6, consistent with lipid-protein interactions involving fully deprotonated CL species and positively charged residues in the protein. Moreover, singlet oxygen formation was specifically observed for tetralinoleoyl CL species and was not observed with monounsaturated and saturated CL species. Our results show that there are at least two mechanisms leading to singlet oxygen formation: one with fast kinetics involving the generation of singlet oxygen directly from CL hydroperoxide decomposition and the other involving CL oxidation. The contribution of the first mechanism was clearly evidenced by the detection of labeled singlet oxygen [O-18(2)((1)Delta(g))] from liposomes supplemented with 18-oxygen-labeled CL hydroperoxides. However quantitative analysis showed that singlet oxygen yield from CL hydroperoxides was minor (<5%) and that most of the singlet oxygen is formed from the second mechanism. Based on these data and previous findings we propose a mechanism of singlet oxygen generation through reactions involving peroxyl radicals (Russell mechanism) and excited triplet carbonyl intermediates (energy transfer mechanism).

End-to-end Distance Distribution in Fluorescent Derivatives of Bradykinin in Interaction with Lipid Vesicles

Cellular membranes have relevant roles in processes related to proteases like human kallikreins and cathepsins. As enzyme and substrate may interact with cell membranes and associated co-factors, it is important to take into account the behavior of peptide substrates in the lipid environment. In this paper we report an study based on energy transfer in two bradykinin derived peptides labeled with the donor-acceptor pair Abz/Eddnp (ortho-aminobenzoic acid/N-[2,4-dinitrophenyl]-ethylenediamine). Time-resolved fluorescence experiments were performed in phosphate buffer and in the presence of large unilamelar vesicles of phospholipids, and of micelles of sodium dodecyl sulphate (SDS). The decay kinetics were analyzed using the program CONTIN to obtain end-to-end distance distribution functions f(r). Despite of the large difference in the number of residues the end-to-end distance of the longer peptide (9 amino acid residues) is only 20 % larger than the values obtained for the shorter peptide (5 amino acid residues). The proline residue, in position 4 of the bradykinin sequence promotes a turn in the longer peptide chain, shortening its end-to-end distance. The surfactant SDS has a strong disorganizing effect, substantially broadening the distance distributions, while temperature increase has mild effects in the flexibility of the chains, causing small increase in the distribution width. The interaction with phospholipid vesicles stabilizes more compact conformations, decreasing end-to-end distances in the peptides. Anisotropy experiments showed that rotational diffusion was not severely affected by the interaction with the vesicles, suggesting a location for the peptides in the surface region of the bilayer, a result consistent with small effect of lipid phase transition on the peptides conformations.

NIR luminescent Er3+/Yb3+ co-doped SiO2-ZrO2 nanostructured planar and channel waveguides: Optical and structural properties

Optical and structural properties of planar and channel waveguides based on sol gel Er3+ and Yb3+ co-doped SiO2-ZrO2 are reported. Microstructured channels with high homogeneous surface profile were written onto the surface of multilayered densified films deposited on SiO2/Si substrates by a femtosecond laser etching technique. The densification of the planar waveguides was evaluated from changes in the refractive index and thickness, with full densification being achieved at 900 degrees C after annealing from 23 up to 500 min, depending on the ZrO2 content Crystal nucleation and growth took place together with densification, thereby producing transparent glass ceramic planar waveguides containing rare earth-doped ZrO2 nanocrystals dispersed in a silica-based glassy host Low roughness and crack-free surface as well as high confinement coefficient were achieved for all the compositions. Enhanced NIR luminescence of the Er3+ ions was observed for the Yb3+- codoped planar waveguides, denoting an efficient energy transfer from the Yb3+ to the Er3+ ion. (C) 2012 Elsevier B.V. All rights reserved.

Efficient plasmonic coupling between Er3+:(Ag/Au) in tellurite glasses

We report a systematic study of the localized surface plasmon resonance effects on the photoluminescence of Er3+-doped tellurite glasses containing Silver or Gold nanoparticles. The Silver and Gold nanoparticles are obtained by means of reduction of Ag ions (Ag+ -> Ag-0) or Au ions (Au3+ -> Au-0) during the melting process followed by the formation of nanoparticles by heat treatment of the glasses. Absorption and photoluminescence spectra reveal particular features of the interaction between the metallic nanoparticles and Er3+ ions. The photoluminescence enhancement observed is due to dipole coupling of Silver nanoparticles with the I-4(13/2) -> I-4(15/2) Er3+ transition and Gold nanoparticles with the H-2(11/2)-> I-4(13/2) (805 nm) and S-4(3/2) -> I-4(13/2) (840 nm) Er3+ transitions. Such process is achieved via an efficient coupling yielding an energy transfer from the nanoparticles to the Er3+ ions, which is confirmed from the theoretical spectra calculated through the decay rate. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.