Luciano A. Bueno

White light generation by frequency upconversion in Tm3+∕Ho3+∕Yb3+-codoped fluorolead germanate glass

White light was produced exploiting an additive synthesis of red, green, and blue fluorescence through frequency upconversion in fluorolead-germanate glass codoped with Ho3+, Tm3+, and Yb3+. The 475, 540, and 650nm signals were, respectively, assigned to thulium (G41-H63) and holmium (S25;F45)→I85 and F55→I85, excited via energy tranfer from ytterbium. The dopant concentrations were adjusted, yielding the emission of a wide color gamut in the visible spectrum and the production of white light using excitation at 975nm. The spectral positions and purity (blue, 97%; green, 100%; red, 95%) of the three colors produced CIE-X=0.3438 and CIE-Y=0.3639 coordinates.

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 1G4 emitting level was accomplished through a multiion interaction involving ground-state absorption of pump photons around 800 nm by the Nd3+(4I9/2→2H9/2, 4F5/2) and Tm3+(3H6→3F4) ions followed by energy-transfer processes involving the Nd3+–Yb3+(4F3/2, 2F7/2→4I11/2, 2F5/2) and Yb3+–Tm3+(2F5/2, 3F4→2F7/2, 1G4) pairs.

Er3+ and Eu3+ containing transparent glass ceramics in the system PbGeO3–PbF2–CdF2

Abstract Glasses with composition 60PbGeO 3 –10PbF 2 –30CdF 2 (mol%) have been obtained in the bulk form with a high stability against crystallization. After doping them with 0.5 mol% of Er 3+ or Eu 3+ and appropriate heat treatment transparent glass ceramics could be obtained. Electronic spectroscopy, X-ray diffraction and transmission electron microscopy measurements have been made. β-PbF 2 : Er 3+ /Eu 3+ single crystals, 5–10 nm in size, are detected in the otherwise transparent composite medium, the size of the particles and absence of clustering allowing for the increased transparency of the final materials.

Structural and spectroscopic study of oxyfluoride glasses and glass-ceramics using europium ion as a structural probe

Universidade Federal Rural de Pernambuco (UFRPE), Dept Fis, Lab Foton, BR-52171900 Recife, PE, Brazil

Generation of wide color gamut visible light in rare-earth triply doped tantalum oxide crystalline ceramic powders

Multicolor visible light emitting near-infrared (NIR)-excited Tm/Ho/Yb-codoped tantalum oxide nanopowders were produced using the sol-gel method. The generation of wide color gamut fluorescence in glass-ceramic with orthorhombic Ta2O5 nanocrystals dispersed into amorphous silica-based matrix is observed. The light emission spectroscopic properties of the rare-earth doped SiO2:Ta2O5 nanocomposites as a function of the tantalum content and temperature of annealing is examined. Simultaneously emitted multicolor fluorescence consisting of blue (480 nm), green (540 nm), and red (650 nm) upconversion signals in the SiO2:Ta2O5 system doped with holmium and thulium and sensitized with ytterbium, is demonstrated. It is also demonstrated that the proper choice of the rare-earth content and the NIR excitation power yielded the generation and control of the three primary colors and allows the emission of a balanced white overall luminescence from the glass-ceramic nanopowder samples.

Characterisation of a new exopolysaccharide obtained from of fermented kefir grains in soymilk

Microbial exopolysaccharides (EPSs) have been widely studied in recent decades due to similarity to gums used in the food industry. Exopolysaccharides can be used in food processing as a thickener and/or stabiliser. This study aimed to investigate the physicochemical properties, thermal behaviour and structural composition of the lyophilised EPS obtained from the fermentation of kefir grains in soymilk. The EPS in concentration 18 mg/mL exhibited water activity of 0.204 and pH=6.20 at 25°C, reducing sugars content of 22.10% (v/v) and protein content of 2% (v/v). The thermogravimetric curve obtained was similar to those reported in the literature for other EPSs. The degradation temperature was 351.84°C and showed that the EPS in this study had a high thermal stability. Characteristic polysaccharide bands were observed in the infrared spectrum. The analysis by liquid chromatography coupled to electrospray ionisation mass spectrometry (LC-ESI-MS) showed that the EPS is only composed of glucose.

Sol–gel entrapped cobalt complex

This work describes optimized conditions for preparation of a cobalt complex entrapped in alumina amorphous materials in the form of powder. The hybrid materials, CoNHG, were obtained by a nonhydrolytic sol–gel route through condensation of aluminum chloride with diisopropylether in the presence of cobalt chloride. The materials were calcined at various temperatures. The presence of cobalt entrapped in the alumina matrix is confirmed by ultraviolet visible spectroscopy. The materials have been characterized by X-ray diffraction (XRD), surface area analysis, thermogravimetric analysis (TGA), differential thermal analyses (DTA) and transmission electron microscopy (TEM). The prepared alumina matrix materials are amorphous, even after heat treatment up to 750 jC. The XRD, TGA/DTA and TEM data support the increase of sample crystallization with increasing temperature. The specific surface area, pore size and pore diameter changed as a function of the heat treatment temperature employed. Different heat treatment temperatures result in materials with different compositions and structures, and influence their catalytic activity. The entrapped cobalt materials calcined at 750 jC efficiently catalyzed the epoxidation of (Z)-cyclooctene using iodozylbenzene as the oxygen donor.

Plant abiotic stress diagnostic by laser induced chlorophyll fluorescence spectral analysis of in vivo leaf tissue of biofuel species

Laser induced fluorescence is exploited to evaluate the effect of abiotic stresses upon the evolution and characteristics of in vivo chlorophyll emission spectra of leaves tissues of brazilian biofuel plants species(Saccharum officinarum and Jatropha curcas). The chlorophyll fluorescence spectra of 20 min predarkened intact leaves were studied employing several excitation wavelengths in the UV-VIS spectral region. Red(Fr) and far-red (FFr) chlorophyll fluorescence emission signals around 685 nm and 735 nm, respectively, were analyzed as a function of the stress intensity and the time of illumination(Kautsky effect). The Chl fluorescence ratio Fr/FFr which is a valuable nondestructive indicator of the chlorophyll content of leaves was investigated during a period of time of 30 days. The dependence of the Chl fluorescence ratio Fr/FFr upon the intensity of the abiotic stress(salinity) was examined. The results indicated that the salinity plays a major hole in the chlorophyll concentration of leaves in both plants spieces, with a significant reduction in the chlorophyll content for NaCl concentrations in the 25 - 200 mM range. The laser induced chlorophyll fluorescence analysis allowed detection of damage caused by salinity in the early stages of the plants growing process, and can be used as an early-warning indicator of salinity stress

Optical properties and energy-transfer frequency upconversion of Yb3+-sensitized Ho3+- and Tb3+-doped lead-cadmium-germanate glass and glass ceramic

In this report we investigate the optical properties and energy-transfer upconversion luminescence of Ho3+- and Tb3+/Yb3+-codoped PbGeO3-PbF2-CdF2 glass-ceramic under infrared excitation. In Ho3+/Yb3+-codoped sample, green (545 nm), red(652 nm), and near-infrared(754 nm) upconversion luminescence corresponding to the 4S2(5F4) → 5I8, 5F5 → 5I8, and 4S2(5F4) → 5I7, respectively, was readly observed. Blue (490 nm) signals assigned to the 5F2,3 → 5I8 transition was also detected. In the Tb3+/Yb3+ system, bright UV-visible emission around 384, 415, 438, 473-490, 545, 587, and 623 nm, identified as due to the 5D3(5G6) → 7FJ(J=6,5,4) and 5D4→7FJ(J=6,5,4,3) transitions, was measured. The comparison of the upconversion process in glass ceramic and its glassy precursor revealed that the former samples present much higher upconversion efficiencies. The dependence of the upconversion emission upon pump power, and doping contents was also examined. The results indicate that successive energy-transfer between ytterbium and holmium ions and cooperative energy-transfer between ytterbium and terbium ions followed by excited-state absorption are the dominant upconversion excitation mechanisms herein involved. The viability of using the samples for three-dimensional solid-state color displays is also discussed.

Upconversion fluorescence spectroscopy in rare earth doped sol-gel nano-glass ceramics

There has recently been a great deal of interest in searching for new materials for application as hosts in infrared-tovisible light upconverters or optical amplifiers based upon rare-earth doped systems. Some of their many applications include: color displays, high density optical recording, biomedical diagnostics, infrared laser viewers and indicators, fiber lasers and amplifiers. Fluorosilicate based sol gel glass ceramics have recently emerged as auspicious candidates for such photonic devices applications. These glasses are advantageous because they present low temperature of preparation, better mechanical strength, chemical durability, and thermal stability than fluoride-based glasses. The present work involves the investigation of optical transitions and upconversion fluorescence spectroscopy of trivalent lanthanide ions Er3+ codoped with Yb3+ in β-PbF2 nanocrystals dispersed in silica glassy matrix, excited with nearinfrared diode lasers. The dependence of the upconversion luminescence upon diode laser power, and the upconversion excitation mechanisms involved are also investigated.