Perylene derivatives with large two-photon-absorption cross-sections for application in optical limiting and upconversion lasing

Perylene tetracarboxylic derivatives (PTCDs) display exceptionally high two-photon absorption (2PA) cross-sections (6, see Figure). In addition, the 2PA saturation behavior and strong two-photon-pumped fluorescence suggest that PTCD compounds may be attractive candidates for applications in optical limiting and two-photon-pumped upconversion lasing.

Incorporation of a liquid crystal to enhance the luminescence properties of Langmuir-Blodgett films of OC1OC6-PPV

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

Al3+ environments in nanostructured ZnAl2O4 and their effects on the luminescence properties

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

Radio luminescence properties of decaoctahedral BaZrO3

Radioluminescence (RL) emissions were obtained for the BaZrO3 self-assembled nanocrystals under decaoctahedral shape, if produced via microwave-assisted hydrothermal method. Trapped F centers created within the band gap are the result of order-disorder effects, which act as key factors supporting significant RL emission through a detrapping process. The influences of size and morphology on RL properties are take into account. No radiation damage or loss of emission intensity was observed. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

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

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

Luminescence quenching by iron in barium aluminoborate glasses

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Optical spectroscopy and frequency upconversion properties of Tm3+ doped tungstate fluorophosphate glasses

Tungstate fluorophosphate glasses of good optical quality were synthesized by fusion of the components and casting under air atmosphere. The absorption spectra from near-infrared to visible were obtained and the Judd-Ofelt parameters determined from the absorption bands. Transition probabilities, excited state lifetimes and transition branching ratios, were, determined from the measurements. Pumping with a 354.7 nm beam from a pulsed laser. resulted in emission at 450 nm. due to transition D-1(2)-->F-3(4) in Tm3+ ions and a broadband emission centered at approximate to 550 nm attributed to the glass matrix. When pumping at 650 nm, two emission bands at 450 nm (D-1(2)-->F-3(4)) and at 790 nm (H-3(4)-->H-3(6)) were observed. Excitation spectra were also obtained in order to understand the origin of both emissions. Theoretical and experimental lifetimes were determined and,the results were explained in terms of multiphonon relaxation. (C) 2003 American Institute of Physics.

Sensitized thulium blue upconversion emission in Nd3+/Tm3+/Yb3+ triply doped lead and cadmium germanate glass excited around 800 nm

Bright blue upconversion emission by thulium ions in PbGeO3-PbF2-CdF2 glass triply doped with Nd3+-Tm3+-Yb3+ under diode laser excitation around 800 nm is reported. The results revealed that the Nd3+/Tm3+/Yb3+-codoped sample generated ten times more 475 nm blue upconversion fluorescence than the Yb3+-sensitized Tm3+-doped one, under the same excitation power. The upconversion process also showed a strong dependence upon the Yb3+ concentration. The results also indicated that the neodymium ions played a major role in the upconversion process by transfering the 800 nm excitation to thulium ions. The population of the Tm3+ ions (1)G(4) emitting level was accomplished through a multiion interaction involving ground-state absorption of pump photons around 800 nm by the Nd3+(I-4(9/2)-->H-2(9/2), F-4(5/2)) and Tm3+(H-3(6)-->F-3(4)) ions followed by energy-transfer processes involving the Nd3+-Yb3+(F-4(3/2), F-2(7/2)-->I-4(11/2), F-2(5/2)) and Yb3+-Tm3+(F-2(5/2), F-3(4)-->F-2(7/2), (1)G(4)) pairs. (C) 2003 American Institute of Physics.

Photo luminescence: A probe for short, medium and long-range self-organization order in ZrTiO4 oxide

Photoluminescent disordered ZrTiO4 powders were obtained by the polymeric precursor soft-chemical method. This oxide system (ordered and disordered) was characterized by photoluminescence, Raman spectroscopy, X-ray diffraction, differential scanning calorimetry and UV vis absorption experiments. The UV absorption tail formation in the disordered oxides was related to the diminution of optical band gap. In the disordered phase, this oxide displayed broad band photoluminescence caused by change in coordination number of titanium and zirconium with oxygen atoms. The gap decreased from 3.09 eV in crystalline oxide to 2.16 eV in disordered oxide. The crystalline oxide presented an orthorhombic alpha-PbO2-type structure in which Zr4+ and Ti4+ were randomly distributed in octahedral coordination polyhedra with oxygen atoms. The amorphous-crystalline transition occurred at almost 700 degrees C, at which point the photoluminescence vanished. The Raman peak at close to 80-200 cm(-1) indicated the presence of locally ordered Ti-O-n and Zr-O-n polyhedra in disordered photoluminescent oxides. (c) 2006 Elsevier B.V. All rights reserved.

EU3+-O2- associates luminescence in Ba2SiO4

Results on the luminescence properties of Eu3+ in Ba2SiO4 sites and the presence of Eu3+-O2- associates are reported. The Ba2SiO4:Eu3+ emission spectra showed two groups of transitions that might be assigned to the D-5(0) --> F-7(0) one. In each group at least two lines were observed. This is possibly related to the different emission centers, attributed to Eu3+ occupying the Ba2+ sites, and to Eu3+-O2- associates in interstices. Excitation spectra presented two CT bands at 270 and 340 nm related to each emission center.

Twentyfold blue upconversion emission enhancement through thermal effects in Pr3+/Yb3+-codoped fluoroindate glasses excited at 1.064 mu m

Infrared-to-visible upconversion emission enhancement through thermal effects in Yb3+-sensitized Pr3+-doped fluoroindate glasses excited at 1.064 mu m is investigated. A twentyfold increase in the 485 nm blue emission intensity as the sample temperature was varied from 20 to 260 degrees C was observed. The visible upconversion fluorescence enhancement is ascribed to the temperature dependent multiphonon-assisted anti-Stokes excitation of the ytterbium sensitizer and excited-state absorption of the praseodymium acceptor. A model based upon conventional rate equations considering a temperature dependent effective absorption cross section for the F-2(7/2)-->F-2(5/2) transition of the Yb3+ and (1)G(4)-->P-3(0) excited-state absorption of the Pr3+, agrees very well with the experimental results. (C) 2000 American Institute of Physics. [S0021-8979(00)08209-8].

Luminescence of Eu(III) beta-diketone complex supported on functionalized macroporous silica matrix

This work reports on the photoluminescent properties of the complex diequatris(thenoyltrifluoroacetonate) europium(III), which was adsorbed or supported on tubes of modified surface silica matrix. The luminescence data and the experimental intensity parameter results evidence the existence of high interactions between the complex [Eu(tta)(3)(H2O)(2)] and the modified surface matrix. The anchored complex on macroporous silica shows higher intensity parameter values suggesting that the Eu-0 bond becomes more covalent than the adsorbed one. Therefore, the hypersensitive character of the D-5(0) --> F-7(2) transition increases evidencing a high contribution of the dynamic coupling mechanism possibly due to highly polarizable chemical environments occupied by europium(III) ion. The lifetimes of the complex on silica matrices were measured. (C) 2001 Elsevier B.V. Ltd. All rights reserved.

Red-green-blue upconversion emission and energy-transfer between Tm3+ and Er3+ ions in tellurite glasses excited at 1.064 mu m

Red, green, and blue emission through frequency upconversion and energy-transfer processes in tellurite glasses doped with Tm3+ and Er3+ excited at 1.064 mum is investigated. The Tm3+/Er3+-codoped samples produced intense upconversion emission signals at around 480, 530, 550 and 660 nm. The 480 nm blue emission was originated from the (1)G(4)-->H-3(6) transition of the Tm3+ ions excited by a multiphoton stepwise phonon-assisted excited-state absorption process. The 5 30, 5 50 nm green and 660 mn red upconversion luminescences were identified as originating from the H-2(11/2), S-4(3/2) --> I-4(15/2) and F-4(9/2) --> I-4(15/2) transitions of the Er3+ ions, respectively, populated via efficient cross-relaxation processes and excited-state absorption. White light generation employing a single infrared excitation source is also examined. (C) 2003 Elsevier B.V. (USA). All rights reserved.

Optical properties and frequency upconversion fluorescence in a Tm3+-doped alkali niobium tellurite glass

Optical spectroscopic properties of Tm3+-doped 60TeO(2)-10GeO(2)-10K(2)O-10Li(2)O-10Nb(2)O(5) glass are reported. The absorption spectra were obtained and radiative parameters were determined using the Judd-Ofelt theory. Characteristics of excited states were studied in two sets of experiments. Excitation at 360 nm originates a relatively narrow band emission at 450 nm attributed to transition D-1(2)-->F-3(4) of the Tm3+ ion with photon energy larger than the band-gap energy of the glass matrix. Excitation at 655 nm originates a frequency upconverted emission at 450 nm (D-1(2)-->F-3(4)) and emission at 790 nm (H-3(4)-->H-3(6)). The radiative lifetimes of levels D-1(2) and H-3(4) were measured and the differences between their experimental values and the theoretical predictions are understood as due to the contribution of energy transfer among Tm3+ ions. (C) 2003 American Institute of Physics.

Origin of photo luminescence in SrTiO3: a combined experimental and theoretical study

A joint experimental and theoretical study has been carried out to rationalize the photoluminescence properties of SrTiO3 perovskite thin films synthesized through a soft chemical processing. Only the amorphous samples present photoluminescence at room temperature. From the theoretical side, first principles quantum mechanical techniques, based on density functional theory at B3LYP level, have been employed to study the electronic structure of a crystalline (ST-c) and an asymmetric (ST-a) model. Electronic properties are analyzed in the light of the experimental results and their relevance in relation to the PL behavior of ST is discussed. (C) 2004 Elsevier B.V. All rights reserved.