Long-wavelength Spectral Region Research Articles

The Pigment World: Life's Origins as Photon-Dissipating Pigments.

Many of the fundamental molecules of life share extraordinary pigment-like optical properties in the long-wavelength UV-C spectral region. These include strong photon absorption and rapid (sub-pico-second) dissipation of the induced electronic excitation energy into heat through peaked conical intersections. These properties have been attributed to a "natural selection" of molecules resistant to the dangerous UV-C light incident on Earth's surface during the Archean. In contrast, the "thermodynamic dissipation theory for the origin of life" argues that, far from being detrimental, UV-C light was, in fact, the thermodynamic potential driving the dissipative structuring of life at its origin. The optical properties were thus the thermodynamic "design goals" of microscopic dissipative structuring of organic UV-C pigments, today known as the "fundamental molecules of life", from common precursors under this light. This "UV-C Pigment World" evolved towards greater solar photon dissipation through more complex dissipative structuring pathways, eventually producing visible pigments to dissipate less energetic, but higher intensity, visible photons up to wavelengths of the "red edge". The propagation and dispersal of organic pigments, catalyzed by animals, and their coupling with abiotic dissipative processes, such as the water cycle, culminated in the apex photon dissipative structure, today's biosphere.

Impact of Glass Irradiation on Laser-Induced Breakdown Spectroscopy Data Analysis.

Increased absorption of optical materials arising from exposure to ionizing radiation must be accounted for to accurately analyze laser-induced breakdown spectroscopy (LIBS) data retrieved from high-radiation environments. We evaluate this effect on two examples that mimic the diagnostics placed within novel nuclear reactor designs. The analysis is performed on LIBS data measured with 1% Xe gas in an ambient He environment and 1% Eu in a molten LiCl-KCl matrix, along with the measured optical absorption from the gamma- and neutron-irradiated low-OH fused silica and sapphire glasses. Significant changes in the number of laser shots required to reach a 3σ detection level are observed for the Eu data, increasing by two orders of magnitude after exposure to a 1.7 × 1017 n/cm2 neutron fluence. For all cases examined, the spectral dependence of absorption results in the introduction of systematic errors. Moreover, if lines from different spectral regions are used to create Boltzmann plots, this attenuation leads to statistically significant changes in the temperatures calculated from the Xe II lines and Eu II lines, lowering them from 8000 ± 610 K to 6900 ± 810 K and from 15,800 ± 400 K to 7200 ± 800 K, respectively, for exposure to the 1.7 × 1017 n/cm2 fluence. The temperature range required for a 95% confidence interval for the calculated temperature is also broadened. In the case of measuring the Xe spectrum, these effects may be mitigated using only the longer-wavelength spectral region, where radiation attenuation is relatively small, or through analysis using the iterative Saha-Boltzmann method.

In-Composition Graded Quantum Barriers for Polarization Manipulation in InGaN-Based Yellow Light-Emitting Diodes

Highly efficient indium gallium nitride (InGaN)-based yellow light-emitting diodes (LEDs) with low efficiency droop have always been pursued for next-generation displays and lighting products. In this work, we report an InGaN quantum barrier (QB) with linear-increase In-composition along [0001] direction for InGaN-based yellow LEDs. With the In-composition in QBs systematically engineered, three QB structures including linear-increase QB (LIQB), linear-decrease QB (LDQB) and commonly used flat QB (FQB) were investigated by simulation. The results show that the LIQB not only yields enhanced electron confinement, but also contributes to suppressed polarization field. Consequently, the yellow LED incorporated with LIQBs demonstrates improved radiative recombination rates and the efficiency droop is alleviated. Under a current density of 100 A/cm2, the efficiency droop ratios of LEDs with FQBs, LDQBs and LIQBs are 58.7%, 62.2% and 51.5%, respectively. When current density varies from 1 A/cm2 to 60 A/cm2, the blueshift values of peak emission wavelength for LEDs with FQBs, LDQBs and LIQBs are 14.4 nm, 16.5 nm and 13.0 nm, respectively. This work is believed to provide a feasible solution for high-performance InGaN-based LEDs in long-wavelength spectral region.

Measurement of Thin Carbon Films Absorption in the Visible Spectrum

The article is devoted to studying radiation absorption in the visible spectrum by thin carbon films. Two types of carbon films, diamond-like and graphite-like, with different structures, are investigated. The films are produced using laser vaporization of the initial material with a further coating of glass substrates. Measurements of light transmission through several samples of films with different thicknesses at three (or more) different areas are obtained for the wavelength range of 400-800 nm using the USB4000 compact fiber-optic spectrometer. The obtained results for the films with different thicknesses demonstrate scant differentiation of values (limiting to the same type of films). The imaginary parts of the films' complex refractive indices (absorption indices) are calculated. The comparison reveals the significant differences (by a factor of two or three) of the absolute values and trends of the absorption indices of diamondlike and graphite-like films. Both types of films are characterized by the expected increase in absorption when transitioning from the long-wavelength spectral region to the short-wavelength one. However, the rate of increase in absorption during such a transition is higher for the diamond-like films. These differences are related to the structure of the films.

Photovoltaic converters with quantum objects under laser flux of subband photons

Quantum objects in the host material of photovoltaic converters can expand the spectral sensitivity to the long-wavelength spectral region. Samples with InAs quantum dots and thin layers in the host GaAs material were studied theoretically with the assumption of high-power laser subband irradiation input. Threshold factors have been established that affect the possibility of radiation heating. For noticeable increase in the temperature of the base material the necessary illumination values were estimated.

Photoluminescence of Nominally Pure Lithium Niobate Single Crystals Produced by Various Technologies

Volume and surface photoluminescence of congruent and stoichiometric lithium niobate crystals obtained using various technologies was studied. The luminescence intensity of the stoichiometric crystal was less than that of the congruent one. Volume luminescence of the crystals was mainly caused by NbLi defects while luminescence quenching of the near-surface layer was observed in the long-wavelength spectral region (>500 nm) because of energy scattering in crystal-lattice vibrations and increased luminescence intensity of the $$ {\mathrm{Nb}}_{\mathrm{Nb}}^{4+}-{\mathrm{O}}^{-} $$ pair. Luminescence bands with maxima at 426 and 446 nm were caused by complex defects in the form of electron–hole pairs $$ {\mathrm{Nb}}_{\mathrm{Nb}}^{4+}-{\mathrm{O}}^{-} $$ in which the Nb atom was bound to oxygen atoms by covalent and ionic bonds. An increase of the Li/Nb ratio led to a shift of the luminescence bands to shorter wavelengths and a change of the fundamental absorption edge of the studied crystals.

Complex Refractive Indices of Zinc Phthalocyanine, Fullerene C70, and Their Mixed Composition

Spectral properties of organic semiconductors (zinc phthalocyanine (ZnPc), fullerene C70, and their mixture (ZnPc : C70) have been studied. The transmission spectra measured in the optical range of 240–1050 nm have been used to obtain spectral dependences of the complex refractive indices with application of numerical simulation methods. It is shown that the absorption spectrum of the mixed composition cannot be presented as a linear superposition of spectra of individual mixture components. The difference between the absorption spectrum of the mixture and superposition of the spectra of individual components is due to the interaction between zinc phthalocyanine and fullerene molecules. This interaction is most pronounced in the long-wavelength spectral region associated with the exciton excitations in ZnPc, where a significant increase in the absorption coefficient and the real part of the complex refractive index is observed.

Experimental studies of efficient sensing fluorescence radiation bands to detect oil and petroleum product spills

We have experimentally studied the laser-induced spectra of petroleum products at the excitation fluorescence wavelength of 266 nm. The paper depicts a schematic diagram of the laboratory setup, gives data resulted from processing of laser-induced fluorescence spectra, and shows that, in comparison with spectra of petroleum products, the laser-induced fluorescence spectra of oil have a shift toward the longer wavelength spectral region and a far wider spectral bandwidth. For oil, an efficient band of sensing fluorescence radiation, is of ~ 390 – 600 nm in average. For gasoline, an efficient band of sensing fluorescence radiation has a significant shift toward the shorter wavelength region (~ 320 – 360 nm) as compared to the efficient sensing fluorescence radiation band for diesel and engine oils (~ 330-395 nm).

The Synthesis Conditions Influence on Silver Nanostructures Formation Under the Effect of Electromagnetic Radiation

In the present work the influence of the synthesis conditions, particularly the effect of used surrounding media on the silver nanostructures formation with various spatial configuration under the effect of the visible electromagnetic radiation has been studied. Silver nanoparticles were synthesized by photostimulated reduction of silver ions from the silver nitrate water solution in aqueous medium and in water yeast extract. The modification of the configuration of resulting nanoobjects was carried out by irradiating the testing samples with red, green, and blue photon flows under the similar conditions. For this task the unique devise with three isolated cells for irradiating silver colloids under the room temperature was developed. The parameters of obtained silver nanostructures were characterized by spectrophotometry and their optical properties have been researched. For the obtained silver colloids the polydispersity indexes were also determined. Besides, the changes in morphology were confirmed by transmission electron microscopy. The shift of the absorption spectra of the testing colloids to the long-wavelength spectral region and their splitting in some cases after irradiation by different wavelength has been showed. For nanoparticles synthesized in the distilled water after irradiating by red, green, and blue photon flows the additional absorption peaks appeared in the longer-wavelength spectral region. Moreover, the colloidal solutions changed the colors after the electromagnetic radiation effect. This indicates the change in nanostructures shapes. The formation of triangular nanoprisms under the influence of red and green photon flows and formation of decahedral nanostructures under the influence of blue light was found. It has been shown that this method can be successfully used to obtain the large silver nanostructures in aqueous solution of the known spatial and optical parameters. The absorption spectrum of the silver nanostructures obtained in water yeast extract shows one clearly expressed peak. But, after irradiation of this colloid with red and green light, the absorption curves are very close in shape to the initial one. Only under the blue light irradiation an additional weak absorption peak can be observed at the wavelength of 523 nm, which might indicates a partial change in the nanostructures shapes. It has been shown that the use of water yeast extract as a surrounding medium for the synthesis of nanoparticles with different spatial morphology minimizes the photoinduced effect of the shape transformation, which was observed in pure aqueous colloids. The effectiveness and the ability to use of different surrounding media for the silver nanoparticles synthesis by photostimulated reduction for obtaining nanostructures with the predetermined spatial parameters and to shift their absorption peaks to the visible and near infrared spectral region has been shown.Ref. 17, fig. 7, tabl. 1.

Resonance reflection of light by ordered silicon nanopillar arrays with the vertical p-n junction

Silicon nanopillar (Si NP) arrays with the axial p-n junction were formed and investigated. A method to fabricate Si NP ordered arrays by means of electron beam lithography using the negative electron resist and reactive ion etching is presented.The effect of strong resonance light scattering – change of the color of separate Si NPs - was demonstrated. One or several minima were registered in the measured reflection spectra. Thereat, the position of reflection minimum was changed with a change in Si NP diameter. A shift of the minimum position towards the longer wavelength spectral region with an increase in Si NP diameter was observed. A shift of the position of minima to the shorter wavelength spectral region with a decrease in Si NP pitch in microarrays with the same Si NP diameter was observed. The quantitative divergence in the position of reflection minima in Si NPs with calculated dependencies for Mie resonances was found. High photosensitivity of Si NP arrays with axial p-n junction to visible and near IR light was discovered. So, these structures may be used for selective photonic sensors.

Optimizing the parameters of a system consisting of a photosensitive IR element based on multilayer structures with quantum wells and a silicon photoelectric multiplexer

This paper discusses the design and process principles involved in optimizing the noise-equivalent temperature difference of photodetectors based on multilayer structures with quantum wells in wide ranges of the structural and process limitations of silicon multiplexers, CMOS-technology design norms, and the parameters of photosensitive elements for the long-wavelength IR spectral region.

Oxidation of atrazine in aqueous media by solar- enhanced Fenton-like process involving persulfate and ferrous ion

The oxidation of s-triazines (using atrazine (ATZ) as a model compound) by a solar-enhanced Fenton-like process involving persulfate and ferrous ion was studied. A flow-through tubular photoreactor was employed for the experiments. The solar-enhanced oxidative system involving ferrous ion and persulfate (Solar/S2O82−/Fe2+) showed the highest ATZ degradation efficiency when compared with other treatments (unactivated S2O82−, Solar - sunlight only, S2O82−/Fe2+, Solar/S2O82−). Complete degradation of ATZ and 20% reduction in total organic carbon (TOC) content were observed after 30min of the treatment. The in situ generated •ОН and SO4–• radicals were shown to be involved in ATZ oxidation using the radical scavengers methanol and tert-butyl alcohol. Furthermore, iron compounds were shown to act not only as catalysts but also as photo-sensitizers, as the introduction of ferrous ion into the reaction mixture led to an increased absorbance of the solution and expansion of the absorption spectrum into the longer wavelength spectral region.

Electrooptical Absorption Measurements (EOAM) Testify Existence of two Conformers of Prodan and Laurdan with Different Dipole Moments in Equilibrium Ground and Franck-Condon Excited State.

The results from the electrooptical absorption measurements (EOAM) on the equilibrium ground and excited Franck-Condon state dipole moments of Prodan and Laurdan in 1,4-dioxane are presented. As follows from experiments Prodan and Laurdan in the equilibrium ground and excited Franck-Condon state have two conformers with considerably different dipole moments. The electrical dipole moments and the transition dipole moment, obtained from the short-wavelength region of the absorption spectrum are parallel. The electrical dipole moments measured at the long-wavelength spectral region are parallel to each other but not parallel to the transition dipole moment m a. The angle θ between the transition dipole moment m a and the dipole moment in the equilibrium ground state μ g of the long-wavelength conformer is about 30(0) for both probes. Obtained results evidence that donor-acceptor pairs of the short-wavelength and long-wavelength conformers are not located on the same axis. Two low-energy conformers of Prodan have been found by density functional theory (DFT) calculations, differing in the orientation of the carbonyl group towards the naphthalene system.

New azobenzene-based chiral-photochromic substances with thermally stable Z-isomers and their use for the induction of a cholesteric mesophase with a phototunable helix pitch

Novel photosensitive azobenzene-containing substances with sorbitol- and lactate-based chiral fragments were synthesized to serve as chiral-photochromic dopants in cholesteric mixtures. Owing to the presence of chlorine or methyl lateral substituents in the azobenzene fragment of the dopants, the photoinduced Z-form of their molecules is highly stable. The photooptical properties of the prepared cholesteric mixtures were studied and it was shown that UV-irradiation of the planarly-oriented films results in a shift of the selective light reflection wavelength to a long-wavelength spectral region due to E–Z isomerization of the azobenzene moieties. This process is thermally and photooptically reversible and the rate of blue-light-induced helix twisting is comparable with the rate of the untwisting process, whereas the thermal relaxation completes only after ca. 40 days at room temperature (for a chlorine-substituted chiral-photochromic dopant). It was found that this value is almost two orders of magnitude less in comparison with the non-substituted chiral-photochromic dopant also studied in this work. The obtained results demonstrate the promising properties of the synthesized compounds for creation of novel photoswitchable cholesteric materials.

Temperature dependence of the parameters of stop bands of globular photonic crystals

The results of the experimental study of the characteristics of stop bands of globular photonic crystals are presented depending of the globule diameter, temperature, and the presence of a dielectric medium in pores between globules. The reflectance spectra of the (111) surface of a globular photonic crystal are analyzed using a fiber-optic technique. As the sample temperature is lowered, the reflectance maximum shifts to the long-wavelength spectral region. The spectral characteristics of stop bands are compared with calculations based on the Wolf-Bragg formula.

Far-red and near infrared BODIPY dyes: synthesis and applications for fluorescent pH probes and bio-imaging.

Far-red and near infrared (NIR) emissive dyes have advantages in the development of fluorescent probes and labelling for bio-imaging in living systems since fluorescence in the long-wavelength region would generate minimum photo-toxicity to biological components, deep tissue penetration and minimal background from auto-fluorescence by bio-molecules. BODIPY dyes are attractive due to their excellent photo-physical properties and potential for fluorescence-based sensing and bio-imaging applications. Thus, numerous research papers have emerged to develop BODIPY-based dyes with absorption and emission in the long-wavelength spectral region (650-900 nm). This review summarizes the general strategies to obtain far-red and NIR BODIPYs. Moreover, their applications for fluorescent pH probes and imaging or labelling in living systems are highlighted.

Electron microscopic study of thin CdS films

The results obtained by investigating the surface morphology and optical properties of thin CdS films formed on transparent glass and glass/indium-tin oxide (ITO) substrates via the chemical and electro-chemical methods are presented. Thin cadmium sulfide films are employed as optical windows in thin-film polycrystalline solar cells. Closely packed cadmium sulfide nanoparticles are observed on the conducting oxide (ITO) surface by means of atomic-force microscopy. Large particles (150–300 nm) comprise smaller particles with sizes of 20–30 nm. Thin CdS layers are characterized by a relatively high level of transmission (∼60%) in the long-wavelength spectral region (520–600 nm).

Intensity of emission from intracenter 4f-transitions in a-Si:H, ZnO, and GaN films doped with rare-earth ions

It is shown that the intensity of emission from intracenter 4f-transitions in amorphous a-Si:H films and crystalline (GaN, ZnO) films doped with rare-earth ions is governed by the local environment of doping impurity ions. In the case of a-Si:H, a pseudo-octahedron with the C4V point group is present due to nanocrystallites, which provides a local environment for rare-earth ions. In the case of a hexagonal crystal lattice in crystalline GaN and ZnO films, the local symmetry of rare-earth ions introduced into the semiconductor matrix by diffusion, with a pseudo-octahedron with the C4V point group, is formed by stresses due to rare-earth ion-oxygen complexes with a radius exceeding that of host ions incorporated at crystal lattice sites. In contrast to GaN films, ZnO films exhibit, on being doped with Tm, Sm, and Yb, both high-intensity emission in the long-wavelength spectral region, characteristic of intracenter 4f transitions in rare-earth ions, and a substantial increase in intensity in the short-wavelength spectral region (λ = 368–370 nm). GaN films doped with rare-earth ions exhibit in this spectral range only an inhomogeneously broadened emission spectrum due to the presence of an emission band characteristic of donor-acceptor recombination.

Formation of the background component of the analytical signal in the long-wavelength region of X-ray fluorescence spectrum

Components of X-ray background in the long-wavelength spectral region of a crystal diffraction X-ray fluorescence spectrometer were calculated. The calculations took into account the bremsstrahlung radiation of free electrons, diffuse scattering and fluorescence of the crystal analyzer, and high-order reflections of the scattered radiation of the fluorescent sample by the crystal analyzer. The results of calculations were compared with the intensities of background samples measured in the region of the NaKα fluorescence line on an SRM-25 wave X-ray spectrometer. The experimental background intensities (response function) well correlate with those found by the regression equation with calculated factors. The importance of particular processes in the formation of X-ray background was assessed.

Optical properties of grooved silicon microstructures: Theory and experiment

The reflection spectra of grooved silicon structures consisting of alternating silicon walls and grooves (air channels) with a period of a = 4-6 μm are studied experimentally and theoretically in the mid� IR spectral range (2-25 μm) upon irradiation of samples by normally incident light polarized along and per� pendicular to silicon layers. The calculation is performed by the scattering matrix method taking into account Rayleigh scattering losses in a grooved layer by adding imaginary parts to the refractive indices of silicon and air in grooved regions. The experimental and calculated reflection spectra are in good agreement in the entire spectral range studied. The analysis of experimental and calculated spectra gave close values of the effective refractive indices and birefringence of the studied structures in the longwavelength spectral region. The val� ues calculated in the effective medium model in the longwavelength approximation ( λ a) gave consider� ably understated values. The obtained results confirm the efficiency of the scattering matrix method for describing the optical properties of silicon microstructures.