Elias A. Silva

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.

Water deficit and salt stress diagnosis through LED induced chlorophyll fluorescence analysis in Jatropha curcas L. oil plants for biodiesel

Light-emitting-diode induced chlorophyll fluorescence analysis is employed to investigate the effect of water and salt stress upon the growth process of physicnut(jatropha curcas) grain oil plants for biofuel. Red(Fr) and far-red (FFr) chlorophyll fluorescence emission signals around 685 nm and 735 nm, respectively, were observed and examined as a function of the stress intensity(salt concentration and water deficit) for a period of time of 30 days. The chlorophyll fluorescence(ChlF) ratio Fr/FFr which is a valuable nondestructive and nonintrusive indicator of the chlorophyll content of leaves was exploited to monitor the level of stress experienced by the jatropha plants. The ChlF technique data indicated that salinity plays a minor role in the chlorophyll concentration of leaves tissues for NaCl concentrations in the 25 to 200 mM range, and results agreed quite well with those obtained using conventional destructive spectrophotometric methods. Nevertheless, for higher NaCl concentrations a noticeable decrease in the Chl content was observed. The Chl fluorescence ratio analysis also permitted detection of damage caused by water deficit in the early stages of the plants growing process. A significant variation of the Fr/FFr ratio was observed sample in the first 10 days of the experiment when one compared control and nonwatered samples. The results suggest that the technique may potentially be applied as an early-warning indicator of stress caused by water deficit.

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

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.

Generation of wide color gamut visible light in NIR-excited thulium-holmium-ytterbium codoped tantalum oxide nanopowders

Multicolor visible light emitting 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.

White light and three-color (RGB) generation by upconversion in fluorogermanate glass for solid state three-dimensional displays

White light was produced exploiting additive synthesis of red, green, and blue(RGB) fluorescence generated through frequency upconversion in fluorogermanate glass samples co-doped with Ho3+, Tm3+ and Yb3+, and excited by a single source of near-infrared radiation. The blue(475 nm), green(540 nm), and red(650 nm), upconversion luminescence signals were, respectively, assigned to thulium(1G4 - 3H6), and holmium(5S2;5F4) → 5I8, 5F5 → 5I8) ions, both excited via successive energy-transfers from ytterbium ions. The Tm3+, Ho3+, and Yb3+ concentrations in the glass host were adjusted yielding the emission of a wide color gamut in the visible spectrum, and the production of white light using a single infrared source of excitation at 975 nm.

Intense red upconversion fluorescence emission in NIR-excited erbium-ytterbium doped laponite-derived phosphor

In this report the optical properties and energy-transfer frequency upconversion luminescence of Er3+/Yb3+-codoped laponite-derived powders under 975 nm infrared excitation is investigated. The 75%(laponite):25%(PbF2) samples doped with erbium and ytterbium ions, generated high intensity red emission around 660 nm and lower intensity green emission around 525, and 545 nm. The observed emission signals were examined as a function of the excitation power and annealing temperature. The results indicate that energy-transfer, and excited-state absorption are the major upconversion excitation mechanism for the erbium excited-state red emitting level. The precursor glass samples were also heat treated at annealing temperatures of 300 °C, 400 °C, 500 °C, and 600 °C, for a 2h period. The dependence of the visible upconversion luminescence emission upon the annealing temperature indicated the existence of an optimum temperature which leads to the generation of the most intense and spectrally pure red emission signal.

Infrared-To-Visible Upconversion Fluorescence Spectroscopy in Trivalent Rare-Earth-Doped Lead-Magnesium-Fluorophosphate Glass

There has recently been a great deal of interest in searching for new vitreous materials for application as hosts in infrared-to-visible 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. Fluorophosphate-based glasses have recently emerged as auspicious candidates for such photonic devices applications. These glasses are advantageous because they present low nonlinear refractive indeces, better mechanical strength, chemical durability, and thermal stability than fluoride-based glasses and are suitable for developing low-loss, high strength, and low-cost optical fibers. It has recently been shown also that the fluorophosphate-based glass is an excellent candidate for high power lasers and broadband amplifiers in the eye-safe region around 1.5 μm for applications in communication, medicine, and meteorology. The present work involves the investigation of optical transitions and upconversion fluorescence spectroscopy of trivalent lanthanide ions Er3+ and Tm3+ codoped with Yb3+ in P2O5-PbO-MgF2 glass, excited with near-infrared diode lasers. The dependence of the upconversion luminescence upon the Yb3+-concentration and diode laser power, and the upconversion excitation mechanisms involved are also investigated. The viability of using these glasses as host for practical applications in optical temperature sensors will also be presented.

Observation of silicon-mediated alleviation of cadmium stress in maize (Zea mays L.) seedlings via LED-induced chlorophyll fluorescence

LED-induced chlorophyll fluorescence analysis is exploited to observe, and monitor the time evolution of silicon-induced alleviation of toxicity in maize (Zea mays L.) seedlings in cadmium contaminated soil. Red, and far-red emissions were examined as a function of cadmium-silicon concentrations, during the 20 days period of the seedlings growing process under stress. The chlorophyll fluorescence spectral analysis provided detection, and evaluation of the damage imposed by the metal stress in the early stages of the plant growing process. The technique also provided the time evolution evaluation of the silicon-induced tolerance enhancement of maize plants to cadmium, which is not viable using conventional in vitro spectral analysis techniques

LED induced chlorophyll fluorescence signatures from leaves of Saccharum officinarum seedlings under water deficit stress

LED-induced chlorophyll fluorescence spectral signatures from Saccharum officinarum leaves are employed to evaluate the effect of water deficit upon the plant growing process. The chlorophyll fluorescence spectral analysis is a nondestructive and nonintrusive indicator of the chlorophyll content of leaves and abiotic stress intensity, and is used to monitor the time evolution of the effect of water deficit stress upon plants physiological state. Red and far-red emission signals around 685 nm and 735 nm, respectively, are observed and examined as a function of irrigation amount. The intensity ratio of the fluorescence emissions allow one to detect signs of damage in the early stages of the plants growing process, and before traces of visible stress became apparent. The results indicated an unusual behavior of the fluorescence ratio for water stress that can potentially be used as a discriminator amongst several abiotic stresses.