Sol-gel deposition of calcium silicate red-emitting luminescent films doped with Eu3+

Eu3+-activated calcium silicate (CaO-SiO2:Eu3+) luminescent films were prepared by the sol-gel method. The structural evolution of the film was studied by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM), and the luminescence properties of the phosphor films were investigated as a function of heat treatment temperature. The XRD study indicates that a kilchoanite phase forms in the film sintered at 800 degreesC, which is different from that in gel powder treated under the same conditions. The SEM results show that the film thickness decreases and the particles in the film become smaller with increasing heat treatment temperature. The CaO-SiO2:Eu film shows the characteristic emission of Eu3+ under UV excitation, with the Eu3+ D-5(0)-->F-7(2) band (616 nm) being the most prominent. A large difference in the Eu3+ lifetime is observed between the film samples treated at 500 and 700 degreesC (or above). Concentration quenching occurs when the Eu3+ doping concentration is above 6 mol% of Ca2+ in the film.

A STUDY ON THE LUMINESCENCE PROPERTIES OF EU3+ AND DY3+ IN M(2)RE(8)(SIO4)(6)O-2 (M=MG, CA RE=Y, GD, LA)

In this paper, the luminescence properties of Eu3+ and Dy3+ in the oxyapatites M(2)RE(8)(SiO4)(6)O-2 (M=Mg, Ca; RE=Y, Gd, La) were studied. The spectral characters of Eu3+ were discussed in relation to the crystal structure. The dependence of the red-to-orange intensity ratio and the position of the charge transfer band of Eu3+ and the yellow-to-blue intensity ratio of Dy3+ together with their fluorescence intensities (I-R for Eu3+ and I-Y for Dy3+) On the M(2+) and the substitution of BO45- and PO43- for SiO44- was discussed. Finally, the concentration quenching of Dy3+ luminescence was reported.

INVESTIGATION ON THE LUMINESCENCE PROPERTIES OF DY3+ AND EU3+ IN M3LN2(BO3)4 (M=CA, SR, BA, LN= LA, GD, Y)

In this paper, the luminescence properties of Dy3+ and Eu3+ in M3Ln2 (BO3)4 (M = Ca,Sr,Ba; Ln = La, Gd, Y) were systematically studied. The hypersensitive transitions of Dy3+ and Eu3+ were investigated in relation to the host compositions; the relationship between the energy of Eu3+ charge-transfer band and M2+ ion was discussed, and the concentration quenching of Dy3+ luminescence was reported.

Studies on Fluorescence Efficiency and Photodegradation of Rhodamine 6G Doped PMMA Using a Dual Beam Thermal Lens Technique

In this paper we report the use of the dual beam thermal lens technique as a quantitative method to determine absolute fluorescence quantum efficiency and concentration quenching of fluorescence emission from rhodamine 6G doped Poly(methyl methacrylate) (PMMA), prepared with different concentrations of the dye. A comparison of the present data with that reported in the literature indicates that the observed variation of fluorescence quantum yield with respect to the dye concentration follows a similar profile as in the earlier reported observations on rhodamine 6G in solution. The photodegradation of the dye molecules under cw laser excitation is also studied using the present method.

Fluorescence Decay Characteristics of the Green Emission From CaF2:Ho3+

Variations in the decay times of the characteristic green emissions at 522.7, 551.3, 549.6, 547.6, 542.2, 540.2, 535.9 and 533.5nm from CaF2 :H03+ with concentration are studied at RT and LNT. A pulsed N2 laser beam of power density 1.5 MW cm-2 is used for the excitation. Temperature dependent concentration quenching of the decay times are observed for all the emission bands. But an increase in the decay time due to the reabsorption process is also observed for a few of the above bands.

1.5 mu m emission and infrared-to-visible frequency upconversion in Er+3/Yb+3-doped phosphoniobate glasses

Sodium phosphoniobate glasses with the composition (mol%) 75NaPO(3)-25Nb(2)O(5) and containing 2 mol% Yb3+ and x mol% Er3+ (0.01 <= x <= 2) were prepared using the conventional melting/casting process. Er3+ emission at 1.5 mu m and infrared-to-visible upconversion emission, upon excitation at 976 nm, are evaluated as a function of the Er3+ concentration. For the lowest Er3+ content, 1.5 mu m emission quantum efficiency was 90%. Increasing the Er3+ concentration up to 2 mol%, the emission quantum efficiency was observed to decrease to 37% due to concentration quenching. The green and red upconversion emission intensity ratio was studied as a function of Yb3+ co-doping and the Er3+-Er3+ energy transfer processes. (c) 2006 Elsevier B.V. All rights reserved.

Luminescence and non-radiative processes in lanthanide squarate hydrates

The luminescence properties of solid hydrated lanthanide squarates (Ln2(C4O4)3(H2O) x; x = 8 or 13;Ln3+ = Gd, La, Eu, Tb, Pr) are reported for temperatures down to 4.2K. The luminescence of the squarate group is observed for the Gd3+ and La3+ compounds at low temperatures (below 150K). The Pr3+ compound does not show any emission at all, not even at 4.2K. This is ascribed to the quenching of the Pr3+ emission by multiphonon relaxation and/or concentration quenching. The quantum efficiencies of the 5D0 emission of Eu3+ and of the 5D4 emission of Tb3+ in these squarate complexes are strikingly different. Whereas the Tb3+ emission shows a temperature independent quantum efficiency of 50% upon ligand excitation, the Eu3+ emission is strongly quenched, showing a temperature dependent quantum efficiency of 0.8% at 4.2K upon ligand excitation. This quenching is ascribed to the low energy position of the charge-transfer state of Eu3+ in these compounds.

Modulação das propriedade ópticas de semicondutores pela incorporação de íons terras raras

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Vidros e vitrocerâmicas em sistemas oxifluoretos

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

The effect of composition, electron irradiation and quenching on ionic conductivity in a new solid polymer electrolyte: (PEG) (x) NH4I

We have prepared, characterized and investigated a new PEG-2000 based solid polymer electrolyte (PEG) x NH4I. Ionic conductivity measurements have been made as a function of salt concentration as well as temperature in the range 265–330 K. Selected compositions of the electrolyte were exposed to a beam of 8 MeV electrons to an accumulated dose of 10 kGy to study the effect on ionic conductivity. The electrolyte samples were also quenched at liquid nitrogen temperature and conductivity measurements were made. The ionic conductivity at room temperature exhibits a characteristic double peak for the composition x = 20 and 70. Both electron beam irradiation and quenching at low temperature have resulted in an increase in conductivity by 1–2 orders of magnitude. The enhancement of conductivity upon irradiation and quenching is interpreted as due to an increase in amorphous region and decrease in crystallinity of the electrolyte. DSC and proton NMR measurements also support this conclusion.

Interaction of rat testis protein, TP, with nucleic acids in vitro. Fluorescence quenching, UV absorption, and thermal denaturation studies

The nucleic acid binding properties of the testis protein, TP, were studied with the help of physical techniques, namely, fluorescence quenching, UV difference absorption spectroscopy, and thermal melting. Results of quenching of tyrosine fluorescence of TP upon its binding to double-stranded and denatured rat liver nucleosome core DNA and poly(rA) suggest that the tyrosine residues of TP interact/intercalate with the bases of these nucleic acids. From the fluorescence quenching data, obtained at 50 mM NaCl concentration, the apparent association constants for binding of TP to native and denatured DNA and poly(rA) were calculated to be 4.4 X 10(3) M-1, 2.86 X 10(4) M-1, and 8.5 X 10(4) M-1, respectively. UV difference absorption spectra upon TP binding to poly(rA) and rat liver core DNA showed a TP-induced hyperchromicity at 260 nm which is suggestive of local melting of poly(rA) and DNA. The results from thermal melting studies of binding of TP to calf thymus DNA at 1 mM NaCl as well as 50 mM NaCl showed that although at 1 mM NaCl TP brings about a slight stabilization of the DNA against thermal melting, a destabilization of the DNA was observed at 50 mM NaCl. From these results it is concluded that TP, having a higher affinity for single-stranded nucleic acids, destabilizes double- stranded DNA, thus behaving like a DNA-melting protein.

Inhibition of self-quenching in thioketones by micellar compartmentalization

The technique of micellar compartmentalization has been used to inhibit the diffusion-controlled self-quenching process in thioketones. By adjusting the ratio of the bulk concentration of the thioketone solute to the bulk concentration of micelles multiple occupancy of the micelles was avoided. Under these conditions enhanced phosphorescence intensity was observed in nitrogen-purged micellar solutions compared with that in acetonitrile solutions, indicating that the thioketone triple was indeed protected from deactivation by a ground statet

High Er3+ concentration low refractive index fluorophosphate glass for evanescent wave optical amplifiers

This is about the first reported laser glass with very low no, high Er3+ concentration and no quenching. In this work, a series of high Er3+ concentration (10.6-12.2 x 10(20) ions/cm(3)), low refractive index (n(1550) < 1.47) and relatively high fluorescence lifetime (6.8-12.6 ms) fluorophosphate glasses were made. A cw-pumping evanescent wave optical amplifier experiment was performed with it, and a relative gain of around 2dB at 1550 nm wavelength was achieved while the noise level was almost unchanged. To our knowledge, this is the first successful relative gain in evanescent wave optical amplifiers (EWOA) demonstrated with cw pumping. It is a valuable study of specially designed fluorophosphate glass suitable for EWOA communication experiment. (C) 2008 Elsevier B.V. All rights reserved.

Modeling and optimizing of high-concentration erbium-doped fiber amplifiers with consideration of ion-clusters

Starting from the modeling of isolated ions and ion-clusters, a closed form rate and power evolution equations for high-concentration erbium-doped fiber amplifiers are constructed. Based on the equations, the effects of the fraction of ion-clusters in total ions and the number of ions per cluster on the performance of high-concentration erbium-doped fiber amplifiers are analyzed numerically. The results show that the presence of the ion-clusters deteriorates amplifier performance, such as the signal power, signal gain, the threshold pump power for zero gain, saturated signal gain, and the maximum gain efficiency, etc. The optimum fiber length or other parameters should be modified with the ion-clusters being taken into account for the amplifiers to achieve a better performance. (c) 2007 Elsevier B.V. All rights reserved.

Formation and Properties of a Novel Heavy-Metal Chalcogenide Glass Doped with a High Dysprosium Concentration

A novel heavy-metal chalcogenide glass doped with a high dysprosium ion (Dy(3+)) concentration was prepared by the well-established melt-quenching technique from high-purity elements. The results show that when Cadmium (Cd) is introduced into chalcogenide glass, the concentration of Dy(3+) ions doped in GeGaCdS glasses is markedly increased, the thermodynamic performance improves, and the difference between T(g) and T(x) is >120 degrees C. The Vickers microhardness is also modified greatly, about 245 kgf/mm(2). The optical spectra indicate that all absorption and emission bands of Dy(3+) are clearly observed and red-shifted with increasing Dy(3+) concentration.