Upconversion luminescence in Er3+ doped and Er3+/Yb3+ codoped zirconia and hafnia nanocrystals excited at 980 nm

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Yttrium oxysulfide nanosized spherical particles doped with Yb and Er or Yb and Tm: efficient materials for up-converting phosphor technology field

This work reports on the preparation, structural and luminescent studies of nanosized up-converter phosphors Y2O2S:Yb(4%), Er(0.1%) and Y2O2S:Yb(4%), Tm(0.1%),both from polymeric and basic carbonate precursors. The precursors were submitted to a sulphuration process that was previously developed for oxysulfide preparation from basic carbonate. From XRD data, all phosphors presented the oxysulfide phase and the mean crystallite size estimated from the Scherrer formula in the range of 15-20 nm. Polymeric precursor leads to the smallest crystallite size independent on the doping ion. SEM and TEM results confirmed that basic carbonate leads to spherical particles with narrow size distribution and mean diameter of 150 nm, and polymeric precursor smaller spherical particles with diameter between 20 and 40 nm. Up-conversion studies under 980 nm laser excitation showed that Er-doped phosphors present strong green emission related to H-2(11/2), S-4(3/2) --> I-4(15/2) Er transitions as well as the red ones, F-4(9/2) --> I-4(15/2). Tm-doped samples show strong blue emission assigned to (1)G(4) --> H-3(6) and also the red ones, related to (1)G(4) --> F-3(4). Therefore, the sulphuration method was successfully applied to prepare nanosized and nanostructured blue and green up-converter oxysulfide phosphors starting from basic carbonate and polymeric precursors. (C) 2003 Elsevier B.V. All rights reserved.

Lead-cadmium oxyfluoride glasses and glass-ceramics

Glasses and glass-ceramics have been obtained in oxyfluoride systems involving lead and cadmium fluorides and one of the well-known glass former oxides SiO2, B2O3 and TeO2. Vitreous domains were established and a wide range of compositions including high heavy metal contents lead to stable glasses. Amorphous structures have been studied by short-range order spectroscopy techniques (Raman scattering and x-ray absorption) and molecular basic structures have been identified. Besides the usual oxides, the role of glass former could also be proposed for cadmium ions. Special attention has been paid for crystallization process. Cubic lead fluoride, cubic lead tellurite, tetragonal tellurium oxide and a solid solution of the type Pb1-xCdxF2 are obtained as crystallization products depending on the composition and temperature of heat treatments. Pb1-xCdxF2 solid solutions are well known superionic materials and obtaining this solid solution as a crystal phase could be very interesting for applications concerning ionic electrical conduction properties. The addition of rare earth ions led to the control of the crystallization process. In the presence of the nucleating ion only the cubic form beta-PbF2 was identified. Rare earth ions are present in the crystal phase and crystal-like spectroscopic properties were observed suggesting interesting applications for these perfectly transparent glass ceramics in photonics.

Multiwavelength visible and white light generation by upconversion emission in Ho/Tm/Yb triply doped fluorogermanate glass-ceramic

Energy transfer excited multiwavelength visible upconversion emission and white light generation is described in a single sample of PbGeO(3)-PbF(2)-CdF(2) glass-ceramic triply doped With Ho/Tm/Yb under single infrared laser excitation. Blue (475 nm), green (540 mn), and red (650 nm), upconversion luminescence signals are generated, and the emissions are assigned, respectively, to thulium ((1)G(4)-(3)H(6)), and holmium ((5)S(2);(5)F(4)) -> (5)I(8), (5)F(5) -> (5)I(8)) ions transitions, both excited via successive energy transfers from ytterbium ions. It is experimentally shown that with a proper combination of the rare earth ions contents, white light may be produced, with the simultaneous generation of fluorescence with controllable intensities at the wavelengths of the three primary colours in a single sample and using a single near-infrared excitation source.

Tm and Tm-Tb-doped germanate glasses for S-band amplifiers

The mechanism involved in the Tm(3+)((3)F(4)) -> Tb(3+)((7)F(0,1,2)) energy transfer as a function of the Tb concentration was investigated in Tm:Tb-doped germanate (GLKZ) glass. The experimental transfer rate was determined from the best fit of the (3)F(4) luminescence decay due to the Tm -> Tb energy transfer using the Burshtein model. The result showed that the 1700 nm emission from (3)F(4) can be completely quenched by 0.8 mol% of Tb(3+). As a consequence, the (7)F(3) state of Tb(3+) interacts with the (3)H(4) upper excited state of TM(3+) slighting decreasing its population. The effective amplification coefficient beta(cm(-1)) that depends on the population density difference Delta n = n((3)H(4))-n((3)F(4)) involved in the optical transition of Tm(3+) (S-band) was calculated by solving the rate equations of the system for continuous pumping with laser at 792 nm, using the Runge-Kutta numerical method including terms of fourth order. The population density inversion An as a function of Tb(3+) concentration was calculated by computational simulation for three pumping intensities, 0.2, 2.2 and 4.4 kWcm(-2). These calculations were performed using the experimental Tm -> Tb transfer rates and the optical constants of the Tm (0.1 mol%) system. It was demonstrated that 0.2 mol% of Tb(3+) propitiates best population density inversion of Tin(3+) maximizing the amplification coefficient of Tm-doped (0.1 mol%) GLKZ glass when operating as laser intensity amplification at 1.47 mu m. (C) 2007 Elsevier B.V. All rights reserved.

Tm3+ and Tm3+-Ho3+ doped fluorogermanate glasses for S-band amplifiers

Two series of glasses with composition (mol%) 70PbGeO3- 15PbF2-15CdF2, the first one with different Tm 3+ contents (0.2, 0.4, 0.6 and 0.8 mol%) and the second one with 0.2 mol% Tm3+ and different Ho3+ contents (0.1, 0.5, 1.0 and 1.5 mol%), have been prepared and some of their spectroscopic properties studied. Absorption in the visible-near infrared and emission in the near infrared region of the electromagnetic spectrum have been obtained. Concerning emission at the 1.4-1.5 μm region, optimization of rare earth ions content leads to 0.2 and 0.5 mol% for Tm3+ and Ho3+, respectively. We discuss potential application of these compositions. © 2005 Elsevier B.V. All rights reserved.

Study of Er3+ fluorescence on tellurite glasses containing Ag nanoparticles

Optical characteristics of tellurite glasses containing silver nanoparticles (NPs) and the influence on the emission spectrum of Er 3+ ions were studied. The transitions 4f ↔ 4f from erbium ions, mainly the 4I13/2 → 4I15/2 transition that involve upconversion energy process, have a strongly dependence with the chemical structure of the rare earth ion. In the present work, silver nanparticles (NPs) embedded in the host vitreous material, show a significant enhance (or quenching) on the erbium fluorescence due the long-range electromagnetic interaction between the plasmon surface energy of the Ag NPs (Localized Surface Plasmon Resonance -LSPR) and the Er3+ ions.

Production and characterization of Tm3+/Yb3+ codoped waveguides based on PbO-GeO2 thin films

Fabrication and optical characterization of Tm3+/Yb3+ codoped PbO-GeO2 (PGO) pedestal-type waveguides are investigated in this work. It is important to mention that, to the best of authors' knowledge, the use of PGO pedestal-type waveguide has not been studied before. PGO thin films codoped with Tm3+ and Yb3+ were obtained through RF magnetron sputtering technique. The pedestal profile was obtained using conventional optical lithography procedures, followed by plasma etching and sputtering deposition. The profile of Tm3+/Yb3+ codoped PGO waveguides was observed by means of Scanning Electron Microscopy (SEM) measurements. Also the infrared and infrared-to-visible frequency upconversion luminescences of Tm3+ ions were measured exciting the samples with a cw 980 nm diode laser. Propagation losses around 11 dB/cm and 9 dB/cm were obtained at 630 and 1050 nm, respectively, for waveguides in the 20-100 μm width range. Single-mode propagation was observed for waveguides width up to 12 μm and 7 μm, at 1050 nm and 630 nm, respectively; larger waveguides width provided multi-mode propagation. The present results corroborate the possibility of using Tm3+/Yb3+ codoped PGO thin films as active waveguide for photonic applications. © 2013 Elsevier B.V. All rights reserved.

Infrared to visible up-conversion emission in Er3+/Yb 3+ codoped fluoro-phosphate glass-ceramics

Erbium Er3+ and ytterbium Yb3+ codoped fluoro-phosphate glasses belonging to the system NaPO3-YF 3-BaF2-CaF2 have been prepared by the classical melt-quenching technique. Glasses containing up to 10 wt% of erbium and ytterbium fluorides have been obtained and characterized using differential scanning calorimetry (DSC) and UV-visible and near-infrared spectroscopy. Transparent and homogeneous glass-ceramics have been then reproducibly synthetized by appropriate heat treatment above glass transition temperature of a selected parent glass. Structural investigations of the crystallization performed through X-ray diffractometry (XRD) and scanning electron microscopy (SEM) have evidenced the formation of fluorite-type cubic crystals based during the devitrification process. Finally, infrared to visible up-conversion emission upon excitation at 975 nm has been studied on the Er3+ and Yb 3+ codoped glass-ceramics as a function of thermal treatment time. A large enhancement of intensity of the up-conversion emissions-about 150 times- has been observed in the glass-ceramics if compared to the parent glass one, suggesting an incorporation of the rare-earth ions (REI) into the crystalline phase. © 2012 The American Ceramic Society.

Enhanced optical properties of germanate and tellurite glasses containing metal or semiconductor nanoparticles

Germanium- and tellurium-based glasses have been largely studied due to their recognized potential for photonics. In this paper, we review our recent studies that include the investigation of the Stokes and anti-Stokes photoluminescence (PL) in different glass systems containing metallic and semiconductor nanoparticles (NPs). In the case of the samples with metallic NPs, the enhanced PL was attributed to the increased local field on the rare-earth ions located in the proximity of the NPs and/or the energy transfer from the metallic NPs to the rare-earth ions. For the glasses containing silicon NPs, the PL enhancement was mainly due to the energy transfer from the NPs to the Er3+ ions. The nonlinear (NL) optical properties of PbO-GeO 2 films containing gold NPs were also investigated. The experiments in the pico- and subpicosecond regimes revealed enhanced values of the NL refractive indices and large NL absorption coefficients in comparison with the films without gold NPs. The reported experiments demonstrate that germanate and tellurite glasses, having appropriate rare-earth ions doping and NPs concentration, are strong candidates for PL-based devices, all-optical switches, and optical limiting. © 2013 Cid Bartolomeu de Araujo et al.

Influência do pH da suspensão coloidal nas propriedades de filmes finos de Sn'O IND. 2'

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

Matrizes semicondutoras GaAs e Sn'X IND. 2' dopado com terras-raras Ce ou Eu: investigação do transporte elétrico

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

Obtenção de espécies moleculares e supramoleculares a partir de reações de auto-montagem entre íons lantanídeos e moléculas orgânicas multilópicas

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Fotoluminescência e transporte elétrico em 'SNO IND. 2' dopado com os íons terras-raras 'ER POT. 3'/' e 'EU POT. 3'/'

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Caracterização estrutural de pós de 'SRTIO IND.3' puro e dopado com samário

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)