Blue Spectral Region Research Articles

Simultaneous imaging/reflectivity measurements to assess diagnostic mirror cleaning

Practical methods to clean ITER's diagnostic mirrors and restore reflectivity will be critical to ITER's plasma operations. We describe a technique to assess the efficacy of mirror cleaning techniques and detect any damage to the mirror surface. The method combines microscopic imaging and reflectivity measurements in the red, green, and blue spectral regions and at selected wavelengths. The method has been applied to laser cleaning of single crystal molybdenum mirrors coated with either carbon or beryllium films 150-420 nm thick. It is suitable for hazardous materials such as beryllium as the mirrors remain sealed in a vacuum chamber.

One‐Step Synthesis and Optical Properties of Benzoate‐ and Biphenolate‐Capped ZrO2 Nanoparticles

AbstractA simple one‐pot approach based on the “benzyl alcohol route” is used for the preparation of benzoate‐ and biphenolate‐capped zirconia and, benzoate‐capped Eu‐doped zirconia nanoparticles. Powder X‐ray diffraction studies and high‐ resolution transmission electron microscopy (HR‐TEM) showed that the nanoparticles present high crystallinity and uniform particle sizes ranging from 3 to 4 nm. FT‐IR and solid state NMR (SS‐NMR) studies revealed that the nanoparticles are coated with a large amount of organic species when the reaction temperature is above 300 °C. It was found that the alcohol used as solvent is oxidized at the surface of the nanoparticles to the respective carboxylic acid which acts as a stabilizer, controlling the nanoparticles growth. The optical properties of these hybrid nanoparticles were studied by room and low (12K) temperature photoluminescence spectroscopy, time‐resolved spectroscopy and absolute emission quantum yield. The as‐synthesized benzoate‐ and biphenolate‐capped nanoparticles exhibit interesting emission properties in the UV and blue spectral regions together with values of emission quantum yields much higher than those reported for zirconia nanoparticles of similar size. The photoluminescent properties were attributed to a cooperative effect of the capping ligands and the defects associated to the ZrO2 nanoparticles. Due to the overlapping of the various emission components involved (i.e., the emission of europium(III) intra‐4f6 transitions, defects in the zirconia and capping ligands) a tunable emission color ranging from purplish‐pink to greenish‐blue could be obtained for the europium‐doped zirconia nanoparticles by simply selecting different excitation wavelengths.

Breast Cancer Therapy Based on Melatonin

The usefulness of melatonin and melatoninergic drugs in breast cancer therapy is based on its Selective Estrogen Receptor Modulator (SERM) and Selective Estrogen Enzyme Modulator (SEEM) properties. Because of the oncostatic properties of melatonin, its nocturnal suppression by light-at-night (LAN) has been considered a risk-factor for breast cancer. Melatonin's SERM actions include modulation of estrogen-regulated cell proliferation, invasiveness and expression of proteins, growth factors and proto-oncogenes (hTERT, p53, p21, TGFβ, E-cadherin, etc.). These actions are observable with physiologic doses of melatonin only in cells expressing ERα, and mediated by MT1 melatonin receptors. Melatonin acts like a SEEM, inhibiting expression and activity of P450 aromatase, estrogen sulfatase and type 1, 17β- hydroxysteroid dehydrogenase, but stimulating that of estrogen sulfotransferase. This double action mechanism (SERM and SEEM), and the specificity for ERα bestows melatonin with potential advantages for breast cancer treatments, associated with other antiestrogenic drugs, and idea already patented. LAN enhances the growth of rat mammary tumors by decreasing or suppressing melatonin production. Epidemiologic studies have also described increased breast cancer risk in women exposed to LAN. Since the strongest suppression of nocturnal melatonin occurs with wavelength light of the blue spectral region, optical and lightening devices filtering the blue light spectrum have been proposed to avoid the risks of light-induced suppression of nocturnal melatonin.

Luminescent urea cross-linked tripodal siloxane-based hybrids

This work reports the synthesis of novel sol–gel derived urea cross-linked tripodal siloxane-based hybrids (classed as tri-ureasils) modified by the addition of phenyltriethoxysilane (PTES) and diphenyldimethoxysilane (DPDMS). The materials were produced as transparent monoliths and thin films (thickness = 3.3–17.5 ± 0.1 μm) and characterized by X-ray diffraction, mid-infrared spectroscopy, 29Si and 13C nuclear magnetic resonance, thermogravimetric analysis, ultraviolet/visible (UV/Vis) absorption and photoluminescence spectroscopies. The role played by PTES and DPDMS as light harvesting chromophores has been discussed and quantified through emission quantum yield and UV/Vis absorption measurements. All the hybrids show efficient emission at room temperature in the blue spectral region with maximum emission quantum yield values ranging from 0.01 ± 0.001 to 0.10 ± 0.01. The highest values were found for the tri-ureasils incorporating PTES and DPDMS essentially due to an increase in the absorption coefficient (from 1.4 × 103 cm−1, for the pristine tri-ureasil, to 8.6 × 103 cm−1, for the hybrids modified by the chromophores). The existence of energy transfer between the DPDMS and PTES excited states and the hybrid host intrinsic emitting levels (NH/C=O- and siliceous-related levels) has been discussed.

Influence of yttrium ions on the emission transfer features of Ce3+/Yb3+ co-doped lithium silicate glasses

Optical absorption and photoluminescence spectra (PL) of the glasses possessing compositions (49−x) Li2O−x Y2O3−50 SiO2:1.0 Ce2O3/1.0Yb2O3 and (49−x) Li2O−x Y2O3−50 SiO2:(0.5 Ce2O3+0.5 Yb2O3) with x varying from 5 to 15mol% were studied. The PL spectra of Ce3+ doped glasses excited at 360nm exhibited two broad parity allowed 5d(2D)→4f(2F5/2,7/2) bands in the blue spectral region, whereas the spectra of Yb3+ doped glasses excited at 900nm exhibited a broad emission band centered at about 980nm due to 2F5/2→2F7/2 transition. A significant enhancement in the intensity of NIR emission is observed due to the sensitization with Ce3+ ions. The increase in the rate of energy transfer from Ce3+ to Yb3+ could be observed with increasing Y2O3 content. The reasons for such improvement have been discussed within a framework of structural modifications taking place in the vicinity of Yb3+ ions.

On the influence of dopant ions on blue emission in kgw crystal excited by infrared laser radiation

The role of doping by Nd3+ and Tm3+ ions in the generation of blue emission in a KGW crystal excited by infrared radiation has been analyzed. Experimental measurements of the emission characteristics and theoretical results of modeling emission spectra of the doping ions are compared. A qualitative difference is shown between the calculated Tm3+ luminescence spectrum and that observed in the experiment. Data on branching ratios of luminescence from the 2P1/2 level of the Nd3+ ions suggest a low emission efficiency from this multiplet in the blue spectral region.

Synthesis and study of the properties of the solid solutions K2Y1−x Tb(Tm) x (MoO4)(PO4) and K2Y1−x Tm x (MoO4)(PO4)0.95(VO4)0.05

The solid solutions K2Y1−x Tb(Tm) x (MoO4)(PO4) and K2Y1−x Tm x (MoO4)(PO4)0.95(VO4)0.05 were synthesized, which are isostructural and crystallize in the orthorhombic crystal system (space group Ibca). The luminescence intensity of the terbium-containing samples increases with increase in the terbium content. The thulium-containing samples are characterized by intense luminescence in the blue spectral region and concentration quenching of luminescence. The introduction of the vanadate anion adversely affects the luminescence intensity.

MODELING THE NEAR-UV BAND OF GK STARS. II. NON-LTE MODELS

We present a grid of atmospheric models and synthetic spectral energy distributions (SEDs) for late-type dwarfs and giants of solar and 1/3 solar metallicity with many opacity sources computed in self-consistent Non-Local Thermodynamic Equilibrium (NLTE), and compare them to the LTE grid of Short & Hauschildt (2010) (Paper I). We describe, for the first time, how the NLTE treatment affects the thermal equilibrium of the atmospheric structure (T(tau) relation) and the SED as a finely sampled function of Teff, log g, and [A/H] among solar metallicity and mildly metal poor red giants. We compare the computed SEDs to the library of observed spectrophotometry described in Paper I across the entire visible band, and in the blue and red regions of the spectrum separately. We find that for the giants of both metallicities, the NLTE models yield best fit Teff values that are ~30 to 90 K lower than those provided by LTE models, while providing greater consistency between \log g values, and, for Arcturus, Teff values, fitted separately to the blue and red spectral regions. There is marginal evidence that NLTE models give more consistent best fit Teff values between the red and blue bands for earlier spectral classes among the solar metallicity GK giants than they do for the later classes, but no model fits the blue band spectrum well for any class. For the two dwarf spectral classes that we are able to study, the effect of NLTE on derived parameters is less significant.

Psychophysical optimization of lighting spectra for naturalness, preference, and chromatic diversity

The optimal spectral profiles of lighting for naturalness, individual preference, and chromatic diversity were estimated with psychophysical experiments in which observers selected illuminants from a set of metamers of D65 to render outdoor and indoor scenes. For naturalness, the illuminant selected was more spectrally structured than daylight and had a low color rendering index. For preference, the illuminant was similar but produced colors a little more saturated. For chromatic diversity, the spectrum was much more structured, with clearly defined peaks in the blue, green, and red spectral regions. These experiments show that light sources with specific structured spectra may have important visual applications in lighting.

Gain comparison in polar and nonpolarsemipolar gallium-nitride-based laser diodes

Experimental gain spectra at continuous-wave (CW) operation of laser diodes (LDs) fabricated from c-plane, nonpolar and semipolar GaN-based materials emitting in violet, blue and green spectral regions are presented. Gain spectra were obtained using the Hakki–Paoli method at high resolution. The ability of the setup to resolve the sharp Fabry–Perot longitudinal peaks of the lasers at all injection currents allowed us to accurately measure the current density to reach transparency on the devices characterized in this work, and determine both total losses and differential modal gain curves up to threshold. We present a comparison of transparency current density and modal gain for nonpolar and c-plane LDs in violet and blue regions. The main parameters for the analysis are the internal electric fields (for c-plane lasers), hole effective masses and valence band splittings. In a preliminary analysis, we investigated the gain spectrum of semipolar green LDs and observed a significantly lower total linewidth (homogeneous plus inhomogeneous) than reported elsewhere, which seems to indicate that inhomogeneous broadening is not the main issue governing the evolution toward high performance green LDs.

Fluorescence quenching in porous silicon/conjugated polymer composites

AbstractMEH‐PPV and m‐LPPP polymers were spin‐coated onto porous silicon (PS). Quenching of the polymer and PS fluorescence has been investigated by means of time‐resolved and steady state fluorescence spectroscopy. Decay kinetics of the PS fluorescence in the blue spectral region attributed to the oxidized silicon surface reveals its quenching by the polymer film. No clear evidence of the opposite process, quenching of the polymer fluorescence by PS has been obtained.

Melt-growth of 1,1,4,4-tetraphenyl-1,3-butadiene crystals on different substrates

We exploit the favourable optical and chemical stability of a model organic semiconductor, 1,1,4,4-tetraphenyl-1,3-butadiene, which is highly emissive in the blue spectral region, to explore crystal melt-growth on several substrates. Different polymorphs were obtained with either monocrystalline or fan-like morphology. We demonstrate the relationship between the optical properties and the crystal structure and morphology.

Using in situ hyperspectral reflectance data to distinguish nine aquatic plant species

In situ hyperspectral reflectance data were studied at 50 bands (10 nm bandwidth) over the 400–900 nm spectral range to determine their potential for distinguishing among nine aquatic plant species: American lotus [Nelumbo lutea (Willd.) Pers.], American pondweed (Potamogeton nodusus Poir.), giant duckweed [Spirodela polyrrhiza (L.) Schleid.], Mexican waterlily (Nymphaea mexicana Zucc.), white waterlily (Nymphaea odorata Aiton), spatterdock [Nuphar lutea (L.) Sm.], giant salvinia (Salvinia molesta Mitchell), waterhyacinth [Eichhornia crassipes (Mart.) Solms] and waterlettuce (Pistia stratiotes L.). The species were studied on three dates: 30 May, 1 July and 3 August 2009. All nine species were studied in July and August, while only eight species were studied in May; giant duckweed was not studied in May due to insufficient availability. Two procedures were used to determine the optimum bands for discriminating among species: multiple comparison range tests and stepwise discriminant analysis. Multiple comparison range tests results for May showed that most separations among species occurred at bands 795–865 nm in the near-infrared (NIR) spectral region where up to six species could be distinguished. For July, few species could be distinguished amongthe 50 bands; most separations occurred at the 715 nm red-NIR edge band where four species could be differentiated. The optimum bands in August occurred in the green (525–595 nm), red (605–635 nm) and red-NIR edge (695–705 nm) spectral regions where up to six species could be distinguished. Stepwise discriminant analysis identified 11 bands in the blue, green, red-NIR edge and NIR spectral regions to be significant to discriminate among the eight species in May. For July and August, stepwise discriminant analysis identified 15bands and 13 bands, respectively, from the blue to NIR regions to be significant for discriminating among the nine species.

Wavelength‐Emission Tuning of ZnO Nanowire‐Based Light‐Emitting Diodes by Cu Doping: Experimental and Computational Insights

AbstractThe band‐gap engineering of doped ZnO nanowires is of the utmost importance for tunable light‐emitting‐diode (LED) applications. A combined experimental and density‐functional theory (DFT) study of ZnO doping by copper (Zn2+ substitution by Cu2+) is presented. ZnO:Cu nanowires are epitaxially grown on magnesium‐doped p‐GaN by electrochemical deposition. The heterojunction is integrated into a LED structure. Efficient charge injection and radiative recombination in the Cu‐doped ZnO nanowires are demonstrated. In the devices, the nanowires act as the light emitters. At room temperature, Cu‐doped ZnO LEDs exhibit low‐threshold emission voltage and electroluminescence emission shifted from the ultraviolet to violet–blue spectral region compared to pure ZnO LEDs. The emission wavelength can be tuned by changing the copper content in the ZnO nanoemitters. The shift is explained by DFT calculations with the appearance of copper d states in the ZnO band‐gap and subsequent gap reduction upon doping. The presented data demonstrate the possibility to tune the band‐gap of ZnO nanowire emitters by copper doping for nano‐LEDs.

The optical properties of rare earth Gd doped ZnO nanocrystals

We present a study of the light emission properties, from UV to blue spectral region, of Gd doped ZnO nanocrystals fabricated by means of a thermal evaporation vapor phase deposition process. The samples were grown from a mixed Zn/Gd source, with a molar percentage of Gd ranging from 0% (pure ZnO) to 5%, 10%, or 15%, in a constant O2/Ar gas mixture flowing at 500°C. The pure ZnO nanocrystals exhibited a strong and predominant UV emission peaking at 375nm. Besides the UV emission of ZnO nanocrystals, two strong blue emissions, located at 432 and 397nm, are observed for the sample doped with 5% Gd. The strong blue emissions are mainly induced by the impurity levels of Gd introduced into the band gap of the ZnO nanocrystals. The UV emission of ZnO decreases as the doping concentration of Gd increases, and the blue emission is replaced by a broad defect emission due to the greater number of defects and impurities, as well as Gd2O3 on the surface. The results show that the optical properties of ZnO can be tuned by the doping concentration of Gd.

Spectral and time-resolved fluorescence signature of four weed species as affected by selected herbicides

In the present study we show for the first time the suitability of the laser-induced fluorescence technique to evaluate in vivo herbicide-induced damages as revealed by changes of fluorescence spectra and lifetime. Four herbicides of different modes of action (glyphosate, bromoxynil, mesotrione, and amitrole) were selected and applied to four weed species ( Stellaria media, Setaria viridis, Chenopodium album, and Viola arvensis). Modifications of the fluorescence signature depended on the agrochemical – plant species interaction as well as on the time after application. Measurements in the red and far-red spectral region reveal disturbances in the functionality of the photosynthetic apparatus and chlorophyll concentration, e.g. after application of bromoxynil or mesotrione. Recordings in the blue and green spectral regions indicate changes of both amount and composition of specific fluorophores, i.e. after application of glyphosate and amitrole. In all spectral measurements, the position of peak maxima was not affected by herbicide application. The fluorescence lifetime, expressed as LT mean or as lifetime 1 (LT1, short-duration) and LT2 (long-duration) fractions, provided additional information to the spectrally resolved data. Thereby, significant alterations of the lifetime duration and fractional characteristics were observed at specific wavelengths, e.g. after application of bromoxynil, mesotrione, or amitrole.

Multicolor Up-Conversion Luminescence in Rare-Earth Doped NaLaF4

In this work we tried to achieve multicolor up-conversion luminescence in low phonon energy material NaLaF4 doped with different Er3+ Tm3+ and Yb3+ concentrations. Up-conversion luminescence was measured and main luminescence bands from Er3+ and Tm3+ in red, green and blue spectral regions were observed. The relative intensities of the luminescence bands could be changed by changing the doping levels of rare-earth ions. Changes in the up-conversion luminescence color could be achieved by applying different infrared pump power density. The color coordinates of the multicolor up-conversion luminescence depending on doping level as well as on the pump power density were presented in CIE (x, y) chromaticity diagram (1931).

Photophysical Properties of 9,10-Disubstituted Anthracene Derivatives in Solution and Films

We have carried out absorption, time-resolved fluorescence, and fluorescence quantum yield measurements of four new soluble anthracene derivatives. They show natural radiative lifetimes in the range of 2.5-4.4 ns, which is 5-10 times shorter than those reported for unsubstituted anthracene. The 9,10-bis(phenylethynyl)anthracene (BPEA) derivatives show the largest fluorescence transition dipoles, which is attributed to extended π-conjugation between anthracene and phenyls through acetylene linkages. Spin-cast films of the BPEA derivatives show strong fluorescence quenching by weakly emitting low energy excitations, which is attributed to excimer-like traps. Quenching is significantly reduced when bulky dendrons are attached so that they give maximum coverage of the emitting chromophore and prevent their aggregation. The results show that anthracene derivatives can be developed into efficient solution-processable fluorescent emitters for the blue and green spectral regions.

Adiabatic frequency conversion of ultrafast pulses

A new method for efficient, broadband sum and difference frequency generation of ultrafast pulses is demonstrated. The principles of the method follow from an analogy between frequency conversion and coherent optical excitation of a two-level system. For conversion of ultrafast pulses, the concepts of adiabatic conversion are developed further in order to account for dispersion and group velocity mismatch. The scheme was implemented using aperiodically poled nonlinear crystals and a single step nonlinear mixing process, leading to conversion of near-IR (∼790 nm) ultrafast pulses into the blue (∼450 nm) and mid-IR (∼3.15 μm) spectral regions. Conversion bandwidths up to 15 THz FWHM and efficiencies up to 50% are reported.

Drop shaped zinc oxide quantum dots and their self-assembly into dendritic nanostructures: Liquid assisted pulsed laser ablation and characterizations

Complex nanostructures and nano-assemblies have exhibited their potential application in the fabrication of future molecular machines and molecular devices. Liquid phase pulsed laser ablation is an easy, versatile, environmental friendly and rapidly growing method for the synthesis of nanostructured materials. Nanosecond pulsed laser ablation of zinc rod placed on the bottom of glass vessel containing methanol is used to produce colloidal solution of drop shaped zinc oxide quantum dots and their self-assembly into various dendritic nanostructures. UV–vis absorption, diffuse reflectance, transmission electron microscopy, and photoluminescence spectroscopy techniques are used for the optical, microscopic, structural and defect diagnosis of obtained colloidal quantum dots and their nano-assemblies. The average length, width and aspect ratio of drop shaped zinc oxide quantum dots are 6±2.4nm, 3.5±1.4nm and 1.69±0.4nm, respectively. Careful investigation of assemblies shows that most of them have linear growth, i.e. growth in longitudinal direction is higher as compared to the transverse direction with three types of classifications as (i) linear axis symmetrical branching, (ii) linear axis asymmetrical branching and (iii) curvilinear axis asymmetrical branching. Photoluminescence spectrum has emission peaks in UV, violet, blue and green spectral region corresponding to the excitonic and various defect related emissions.