Monochromatic Light Of Different Wavelengths Research Articles

Selective and Sensitive Photon Sieve Based on III–V Semiconductor Nanowire Forest Fabricated by Lithography‐Free Process

AbstractVertically oriented semiconductor nanowires (NWs) have been intensely studied in macroscopic perspective due to their attractive applications such as optical filters, photodiodes, and solar cells. However, microscopic photonic phenomena of dense and random NWs have been rarely, and their promising applications have not been explored. Therefore, this article theoretically and experimentally investigates the microscopic photonic event of dense and random NWs using highly selective and sensitive photon sieve (SSPS), which employs highly populated III/V semiconductor NW forests fabricated with a lithography‐free self‐catalyzed growth method. Theoretical analyses reveal that diameter‐dependent and selective photon absorption occurs even for a dense and disordered NW distribution. The engineered growth process affords highly populated NW forests (mean shortest interval = 192.4 nm) comprising NWs with a high aspect ratio (mean aspect ratio = 34.3) and a sufficiently broad diameter distribution to span the visible spectrum and decompose it (mean diameter = 94 nm, standard deviation = 49 nm). Moreover, the SSPS exhibits unique spectral responses to monochromatic light of different wavelengths (correlation coefficients < 0.03) and a high sensitivity with a highest absorptivity of 92.4%. This work indicates SSPSs can be utilized for various applications of artificial photoreceptor, physically unclonable function, and high efficient optoelectronics.

Influence of different spectral ranges of light and Ca2+ -channel blockers on Ca2+ and K+ levels in Phaseolus coccineus L. pulvini

The effect of different spectral ranges of light on the modification of transport processes in isolated parts of <i>Phaseolus coccineus</i> pulvini was analysed in a bath medium by determining the Ca<sup>2+</sup> and K<sup>+</sup> contents. After 1 h incubation of separated fragments of the extensor and flexor in solutions containing deionized water, medium, or medium with verapamil or nifedipine, the investigated material was irradiated with monochromatic light of different wavelengths. The concentration of Ca<sup>2+</sup>, K<sup>+</sup> and the pH value were determined in the medium. The obtained results suggest the occurrence of a specific coupling between the concentration of Ca<sup>2+</sup> and K<sup>+</sup> dependend on the wavelength of the applied light and part of the pulvinus. Certain spectral ranges of light brought about opposite effects on ion transport in opposite parts of the pulvinus. Changes in the pH of mediums containing isolated parts of the pulvini part to different effects of blue, red, and far-red light on the activity of H<sup>+</sup>-pumps located in the motor cells. The use of verapamil and nifedipine, specific Ca<sup>2+</sup>-channel blockers, made it possible to demonstrate the significant effect of Ca<sup>2+</sup> on the activity and functioning of K<sup>+</sup> -channels. The two types of inhibitors decreased the influx of Ca<sup>2+</sup> and K<sup>+</sup> to motor cells of the pulvini, however they did not limit the efflux of ions to the medium. The obtained results suggest that Ca<sup>2+</sup> ions take part in transduction of the light signal. It seems probable that the action of blue light is also mediated by part of the Ca<sup>2+</sup> ions.

Phototactic behaviour in Aphidius gifuensis (Hymenoptera:Braconidae)

We investigated the spectral sensitivity and response to light intensity of Aphidius gifuensis (Hymenoptera: Braconidae), a key natural enemy of the green peach aphid, Myzus persicae (Hemiptera: Aphididae). We used 15 monochromatic lights (emitting various specific wavelengths from 340 to 689 nm) and white light. Monochromatic light of different wavelengths and white light elicited photopositive behaviour from A. gifuensis. The strongest response was stimulated by blue light (492 nm), which induced a movement of 43.5 cm, a response that differed from all other groups. This was followed by green light (568 nm) and UV-light (380 nm). There was no significant response to orange light (601 nm) or red light (649, 668 and 689 nm) from A. gifuensis. The response intensity curve for A. gifuensis to monochromatic light (492 nm) decreased as light intensity increased. At 568 nm, the phototactic response showed an ‘S’ shaped curve. But at 628 nm, the phototactic response rose continuously with increasing intensity. We report here that the visual system of A. gifuensis is composed of three spectrum receptors, attuned to UV, blue and green light. While light intensity is a key factor in determining the photopositive response of A. gifuensis, the effect of intensity varies by wavelength.

Visible luminescence in photo-electrochemically etched p-type porous silicon: Effect of illumination wavelength

The effect of low power density of ~ 5 μW/cm 2 monochromatic light of different wavelengths on the visible photoluminescence (PL) properties of photo-electrochemically formed p-type porous silicon (PS) has been investigated. Two-peak PL “red” and “green” is resolved in PS samples etched under blue-green wavelength illumination; 480, 533 and 580 nm. It is found that the weight of “green” PL has maxima for the sample illuminated with 533 nm wavelength. Whereas, PL spectra of PS prepared under the influence of red illumination or in dark does not exhibit “green” PL band, but shows considerable enhancement in the “red” PL peak intensity. Fourier transform infrared (FTIR) spectroscopic analysis reveals the relationship between the structures of chemical bonding in PS and the observed PL behavior. In particular, the PL efficiency is highly affected by the alteration of the relative content of hydride, oxide and hydroxyl species. Moreover, relative content of hydroxyl group with respect to oxide bonding is seen to have strong relationship to the blue PL. Although, the estimated energy gap value of PS samples shows a considerable enlargement with respect to that of bulk c-Si, the FTIR, low temperature PL and Raman measurements and analysis have inconsistency with quantum confinement of PS.

Modeling bilayer polymer/fullerene photovoltaic devices

We investigate the transport properties of organic photovoltaic devices formed by a heterojunction of a semiconducting polymer poly {3-[4′-(1″,4″,7″-trioxaoctyl) phenyl] thiophene} and the fullerene (C60). Under monochromatic light of different wavelengths we measure the current-voltage (I–V) characteristic of diodes with variable thickness of the C60 layer. We propose an analytical model assuming that; (i) holes are created in the polymer by charge carrier generation at the heterojunction; and (ii) the C60 layer behaves like a photoconductor under illumination. By using the electrical conductivity of the C60 layer as fitting parameter we reproduce quite well the experimental data, including the I–V curves and the changes of the open-circuit voltage with the variation of the C60 layer thickness. We show that the values of the conductivity are closely related to the fullerene optical absorption coefficient, implying a large contribution of the C60 film to the diode photocurrent.

Diagnostics of Recombination Rate Homogeneity in Structures of Large-Area Solar Cells

The paper refers about a possibility to check recombination rate distribution over the area of power (large-area) solar cells from measured values of open circuit voltage VOC using local irradiation by monochromatic light of different wavelengths (LBIV . Light Beam Initiated Voltage). The method can give information both about recombination centres distribution in large-area solar cells and surface recombination rate at the antireflection coating. From VOC distribution, also position and extent of local defects can also be determined. The method can be used to investigate the influence of technology on characteristics of solar cells as an in-process checking with the aim of increasing efficiency and reliability of solar cells.

A spectroscopic study of photoirradiated cellulose

The influence of photoirradiation on cellulose was studied by means of fluorescence, Fourier transform IR and UV—visible reflectance spectroscopy. Samples of cellulose were irradiated with the entire spectrum of a medium pressure Hg lamp, with the light from the Hg lamp filtered through a glass filter, or selectively with monochromatic light of different wavelengths. The emission spectra of untreated cellulose samples and of differently irradiated samples were recorded after various exposure times. Irradiation with the unfiltered radiation from the Hg lamp caused a strong increase in the emission intensity and a gradual shift in the emission maximum to longer wavelengths. After irradiation for 96 h a pronounced band at 1733 cm −1 was seen in the diffuse reflectance IR Fourier transform spectrum of the sample, indicating the formation of carbonyl groups as a result of the treatment. Irradiation with filtered light from the Hg lamp caused a small decrease in the emission intensity and shifted the emission maximum from 445 to 462 nm. Exposure of cellulose to monochromatic light of 350 nm wavelength caused a gradual fading of the fluorescence with increased exposure time and a small shift in the emission maximum to longer wavelengths. After the sample had been allowed to stand in the dark, the emission intensity was almost completely restored to its original value, but the red shift of the emission maximum caused by the irradiation remained unchanged.

Factors affecting gene expression of patatin and proteinase-inhibitor-II gene families in detached potato leaves:

In whole intact potato (Solanum tuberosum L.) plants, the gene families of class-I patatin and proteinase inhibitor II (Pin 2) are constitutively expressed in the tubers. However, they are also induced in detached potato leaves in the presence of light. To further characterize this light action, the detached leaves were subjected to monochromatic light of different wavelengths and to darkness in the presence of metabolites and inhibitors. Patatin genes could be induced by the simultaneous application of sucrose (sugars) and glutamine in darkness. Neither of these metabolites was active when supplied alone. When photosynthesis was blocked by 3-(3,4-Di-chlorophenyl)-1, 1-dimethylurea (DCMU) in the light, patatin genes were not expressed; however, the inhibition was overcome in the presence of sucrose. This indicates that besides its role in photosynthetic carbohydrate production, light may be essential for the supply of amino acids (or reduced nitrogen). Unlike patatin, Pin 2 genes were, to a small extent, also active in darkness, and sucrose weakly enhanced this expression. However, DCMU did not affect Pin 2 expression in the light. Both abscisic acid and methyl jasmonate strongly promoted the accumulation of Pin 2 mRNA independent of the light conditions, indicating that the gene family is probably under hormonal control. The phytohormones did not affect patatin gene expression. Inhibitors of cytosolic (cycloheximide) and organellar (chloramphenicol) translation had opposite effects on the two gene families. Careful evaluation of the inhibitors' action indicates that protein synthesis (cytosol) is required for the expression of Pin 2 genes but not for the patatin genes. These results clearly demonstrate that, although in situ both gene families are constitutively expressed in the same plant organ (tuber) in intact plants, their expression is mediated by different factors.

EFFECT OF LIGHT QUALITY ON THE in vitro THYLAKOID PROTEIN PHOSPHORYLATION IN THE GREEN ALGA Scenedesmus obliquus

Abstract Thylakoid protein phosphorylation was assayed in vitro with isolated thylakoids of Scenedesmus obliquus by irradiation with monochromatic light of different wavelengths and equal photon fluences. The action spectrum for light‐activated protein phosphorylation showed two maxima at 450 and 679 nm. A minimum of activity was reached around 580 nm. At this wavelength, the level of protein phosphorylation barely differed from that of dark‐incubated samples. The action spectrum of thylakoid protein phosphorylation resembled the chlorophyll absorption spectrum obtained in vivo. The results show that chlorophyll is the photoreceptor for thylakoid membrane phosphorylation.

The effect of light intensity and temperature on the transient photoconductivity in thin a-Se 80Te 20 films

Transient photoconductivity measurements have been made in vacuum-evaporated thin films of Se 80Te 20. It has been observed that the rise of the photocurrent shows an anomalous behaviour. The photocurrent passes through a maximum before attaining the steady state. This anomalous behaviour has been studied at different temperatures by shining monochromatic light of different wavelengths and intensities. The results have been explained in terms of a recombination mechanism in this material.

Action Spectrum for Interaction between Visible and Far-Red Light on Face Chloroplast Orientation in Mougeotia

The orientation of chloroplasts from profile to face position in Mougeotia can be controlled in two ways: by a typical phytochrome-mediated system or by continuous, simultaneous irradiation with far-red and visible light. In experiments with dichromatic irradiation of Mougeotia, the light conditions applied prevented the formation of a far-red-absorbing form of phytochrome gradient in the cell. An unpolarized background of far-red light and linearly polarized monochromatic light of different wavelengths and vibrating parallel to the cell axis, if given by themselves, were completely ineffective in producing any changes in chloroplast orientation. Given together, however, changes in chloroplast orientation were induced. The action spectrum for this interaction between constant far-red and variable visible light was maximal at 620 nanometers. The chloroplast response in these dichromatic light conditions required a prolonged duration of exposure to simultaneous continuous irradiation of high fluence energy. The vibrating plane of linearly polarized 620 nanometer light had no significant influence on interaction with far-red light in chloroplast movement. The results obtained are different from the typical low energy phytochrome-mediated chloroplast orientation. This new type of chloroplast photoresponse might be mediated by an unknown sensory pigment.

Anomalous rise of photocurrent in amorphous thin films of Ge 22Se 78

Transient photoconductivity measurements have been made in vacuum evaporated thin films of Ge 22Se 78. It has been observed that, under certain experimental conditions, the rise of photocurrent shows an anomalous behaviour. Before attaining the steady state, the photocurrent passes through a maximum. This anomalous behaviour has been studied at different temperatures by shining monochromatic light of different wavelengths and intensities. The results have been explained in terms of recombination mechanism in this material.

Localization of visual pigments within rhabdoms of the compound eye of Spodoptera exempta (Insecta, Noctuidae)

In the noctuid moth Spodoptera exempta, the distribution of visual pigments within the fused rhabdoms of the compound eyes was investigated by electron microscopy. Each ommatidium regularly contains eight receptor cells belonging to three morphological types: one distal, six medial, and one basal cell (Meinecke 1981); four different visual pigments — absorption maxima at approximately 355, 465, 515, and 560 nm — are known to occur within the eye (Langer et al. 1979). The compound eyes were illuminated in situ by use of monochromatic light of different wavelengths. This illumination produced a wide scale of structural changes in the microvilli of the rhabdomeres of individual cells. Preparation of eyes by freeze-substitution revealed the structural changes in the rhabdomeres to be effects of light occurring in vivo. The degree of structural changes may be considerably different in rhabdomeres within the same ommatidium; it was found to depend on the wavelength and the duration of illumination, the intensity received by the ommatidia as well as the spectral sensitivity of the receptor cells. Therefore, it was possible to estimate the spectral sensitivities of the morphological types of receptor cells. Generally, all medial cells are green receptors and all basal cells red receptors; distal cells are blue receptors in about two-thirds of the ommatidia, while in the remaining third of them distal cells are sensitive to ultraviolet light.

Photomechanical effects in photochromic systems

Abstract

The Spectral Response of Light Dependent Chlorophyll b Formation

AbstractDark grown seedlings of barley will obtain a high ratio chlorophyll a/chlorophyll b when exposed to intermittent light (1 min of incandescent light or one electronic flash every hour). Such material has been exposed to monochromatic light of different wavelengths for 1 h. The ratio a/b gets a minimum in light of 670 nm, indicating the highest rate of chlorophyll b formation at this wavelength. The possibility is discussed that the light absorber (and also precursor) could be a short‐lived chlorophyll a form, existing prior to the forms in the Shibata‐shift. Chlorophyll b formation in darkness is discussed from the findings that the rate of formation of chlorophyll b is higher in intermittent light than it should be, calculated from the rate in continuous light, where the saturation intensity is rather low.

Optics and phase relationships of the optically anisotropic C 3A

The birefringence (γ−β) of each optically anisotropic variety of C 3A has been measured as a function of temperature in monochromatic light of different wavelengths. The orthorhombic phase remains structurally unchanged up to the decomposition temperature, and the orientation of the optic axial plane and dispersion of 2V X change during heating. The optic orientation and dispersion type of the monoclinic phase above the transition point indicate that this phase transforms reversibly into the orthorhombic phase.

Link between rhodopsin and disk membrane cyclic nucleotide phosphodiesterase. Action spectrum and sensitivity to illumination

Frog (Rana pipiens) rod outer segment disc membranes contain guanosine 3',5'-cyclic monophosphate phosphodiesterase (EC 3.1.4.1.c) which, in the presence of ATP, is stimulated 5- to 20-fold by illumination. The effectiveness of monochromatic light of different wavelengths in activating phosphodiesterase was examined. The action spectrum has a maximum of 500 nm, and the entire spectrum from 350 to 800 nm closely matches the absorption spectrum of rhodopsin, which is apparently the pigment which mediates the effects of light on phosphodiesterase activity. trans-Retinal alone does not mimic light. Half-maximal activation of the phosphodiesterase occurs with a light exposure which bleaches 1/2000 of the rhodopsins. Half-maximal activation can also be achieved by mixing 1 part of illuminated disc membranes in which the rhodopsin is bleached with 99 parts of unilluminated membranes. Regeneration of bleached rhodopsin by addition of 11-cis-retinal is illuminated disc membranes reverses the ability of these membranes to activate phosphodiesterase in unilluminated membranes. If the rhodopsin regenerated by 11-cis-retinal is illuminated again, it regains the ability to activate phosphodiesterase. These studies show that the levels of cyclic nucleotides in vetebrate rod outer segments are regulated by minute amounts of light and clearly indicate that rhodopsin is the photopigment whose state of illumination is closely linked to the enzymatic activity of disc membrane phosphodiesterase.

Long-term adaptation by different monochromatic light in the photoreceptors of three crustacean species

Long-term adaptation by monochromatic light of different wavelengths and equal stimulus efficiency was tested in the photoreceptors of Carcinus (= Carcinides) maenas L., Eupagurus bernhardus L., and Astacus leptodactylus Eschscholz. The characteristic course of light and dark adaptation was compared for these species. Addition of glucose in the saline caused faster dark adaptation, probably due to electrogenic pump activity. Adaptation effects by weak and stronger light were equal for all wavelengths used (between 409 and 611 nm). The results indicate that the observed light and dark adaptation consists both in pigment and in membrane adaptation. Photoreversal of bleaching could not be proved. The results with Astacus can be explained by photoreversal and/or by selective adaptation of two different receptors of different spectral sensitivity. In Eupagurus colour vision seems to be improbable.

Determination of copolymer composition by a polarization diffusometer using monochromatic light of different wavelengths

A method is proposed for determining the composition of copolymers, which is based on the additive nature of refractive index increments of copolymer components. According to this method, in order to increase the sensitivity and accuracy of determining composition, the increments are measured using a Tsvetkov polarization diffusometer in monochromatic light of different wavelengths.

Photosynthesis: A Simple Demonstration of the Emerson Enhancement Effect

Photosynthesis is perhaps the single most important living process. However, the rapid advances within the last 25 years have resulted in a dearth of simple experiments that can demonstrate the basis of our present understanding. The experiment described here illustrates the operation of two separate light reactions in photosynthesis by showing the Emerson enhancement effect. The efficiency of photosynthesis has been found to vary as plants are illuminated with monochromatic light of different wavelengths. One common finding has been that the efficiency of photosynthesis decreases with the use of longer wavelengths of light. The decline in photosynthetic rate occurs in spite of strong light-absorption by chlorophyll. Robert Emerson (1957) and his colleagues discovered that the low rate of photosynthesis in long-wavelength light could be overcome, or even surpassed, by simultaneously illuminating the plants with a second beam of shorter-wavelength light. The rate of photosynthesis in the combined light beams was greater than could be expected by adding the rates found when either beam was provided alone. This relative excess of photosynthesis is known as the Emerson enhancement effect. One conclusion that Emerson reached on the basis of his discovery was that photosynthesis involves two photochemical processes. The exact, detailed explanations of how these two processes are achieved by the chlorophyll and accessory pigments have been modified considerably since Emerson published his work. Howevrer,