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Light : the visible spectrum and beyond
A visual exploration of the power and behavior of light across the entire electromagnetic spectrum reveals how types ranging from radio waves to X-rays affect life on earth and throughout the universe. --Publisher.
Book
Leaf chlorophyll parameters and photosynthetic characteristic variations with stand age in a typical desert species (Haloxylon ammodendron)
As a desert shrub, Haloxylon ammodendron combines ecological, economic, and social benefits and plays an important role in the ecological conservation of arid desert areas. Understanding its physiological characteristics and its mechanism of light energy utilization is important for the conservation and utilization of H. ammodendron . Therefore, we selected five stands (5-, 11-, 22-, 34-, and 46-year-old) of H. ammodendron as research objects in the study and measured their photosynthetic light response curves by a portable open photosynthesis system (Li-6400) with a red-blue light source (6400-02B). Then, we measured the leaf chlorophyll parameters in the laboratory, calculated the photosynthetic characteristics by using Ye Zipiao’s photosynthetic model, analyzed their variation patterns across stand ages, and explored the relationships between leaf chlorophyll parameters and photosynthetic characteristics. The results showed that leaf chlorophyll parameters and photosynthetic characteristics of H. ammodendron at different stand ages were significantly different. Chl content, P nmax , and LUE max of H. ammodendron were V-shaped with the increase of stand age. The 5-year-old H. ammodendron was in the rapid growth period, synthesized more Chl a+b content (8.47 mg g −1 ) only by using a narrower range of light, and the P nmax and LUE max were the highest with values of 36.21 μmol m −2 s −1 and 0.0344, respectively. For the 22-year-old H. ammodendron , due to environmental stress, the values of Chl a+b content, P nmax , and LUE max were the smallest and were 2.64 mg g −1 , 25.73 μmol m −2 s −1 , and 0.0264, respectively. For the older H. ammodendron , its Chl content, P nmax , and LUE max were not significantly different and tended to stabilize but were slightly higher than those of the middle-aged H. ammodendron . On the other hand, the other photosynthetic parameters did not show significant variation patterns with stand age, such as R d , AQE, LSP, LCP, and I L-sat . In addition, we found that the relationships between Chl a+b content and P nmax and between Chl a+b content and LUE max were highly correlated, except for the older H. ammodendron . Thus, using leaf chlorophyll content as a proxy for photosynthetic capacity and light use efficiency should be considered with caution. This work will provide a scientific reference for the sustainable management of desert ecosystems and vegetation restoration in sandy areas.
Journal Article
Correlations between allocation to foliar phosphorus fractions and maintenance of photosynthetic integrity in six mangrove populations as affected by chilling
• Chilling restrains the distribution of mangroves. We tested whether foliar phosphorus (P) fractions and gene expression are associated with cold tolerance in mangrove species.
• We exposed seedlings of six mangrove populations from different latitudes to favorable, chilling and recovery treatments, and measured their foliar P concentrations and fractions, photochemistry, nighttime respiration, and gene expression.
• A Kandelia obovata (KO; 26.45°N) population completely and a Bruguiera gymnorhiza (Guangxi) (BGG; 21.50°N) population partially (30%) survived chilling. Avicennia marina (24.29°N), and other B. gymnorhiza (26.66°N, 24.40°N, and 19.62°N) populations died after chilling. Photosystems of KO and photosystem I of BGG were least injured. During chilling, leaf P fractions, except nucleic acid P in three populations, declined and photoinhibition and nighttime respiration increased in all populations, with the greatest impact in B. gymnorhiza. Leaf nucleic acid P was positively correlated with photochemical efficiency during recovery and nighttime respiration across populations for each treatment.
• Relatively high concentrations of nucleic acid P and metabolite P were associated with stronger chilling tolerance in KO. Bruguiera gymnorhiza exhibited relatively low concentrations of organic P in favorable and chilling conditions, but its partially survived population showed stronger compensation in nucleic acid P and Pi concentrations and gene expression during recovery.
Journal Article
Influence of the variation potential on photosynthetic flows of light energy and electrons in pea
Local damage (mainly burning, heating, and mechanical wounding) induces propagation of electrical signals, namely, variation potentials, which are important signals during the life of plants that regulate different physiological processes, including photosynthesis. It is known that the variation potential decreases the rate of CO2 assimilation by the Calvin–Benson cycle; however, its influence on light reactions has been poorly investigated. The aim of our work was to investigate the influence of the variation potential on the light energy flow that is absorbed, trapped and dissipated per active reaction centre in photosystem II and on the flow of electrons through the chloroplast electron transport chain. We analysed chlorophyll fluorescence in pea leaves using JIP-test and PAM-fluorometry; we also investigated delayed fluorescence. The electrical signals were registered using extracellular electrodes. We showed that the burning-induced variation potential stimulated a nonphotochemical loss of energy in photosystem II under dark conditions. It was also shown that the variation potential gradually increased the flow of light energy absorbed, trapped and dissipated by photosystem II. These changes were likely caused by an increase in the fraction of absorbed light distributed to photosystem II. In addition, the variation potential induced a transient increase in electron flow through the photosynthetic electron transport chain. Some probable mechanisms for the influence of the variation potential on the light reactions of photosynthesis (including the potential role of intracellular pH decrease) are discussed in the work.
Journal Article
Characteristics of Dye-Sensitized Solar Cell under PWM Illumination: Toward Indoor Light-Energy Harvesting in the Solid-State Lighting Era
The dye-sensitized solar cell (DSSC) has been on the market as a permanent power source for indoor IoT edge devices. In recent years, indoor illumination technology has been experiencing a drastic transition from incandescent and fluorescent lamps toward solid-state lighting devices with light-emitting diodes (LEDs). In addition to the high power efficiency, a virtue of LEDs is their prompt response, which enables precise change of the illumination level using pulse-width modulation (PWM) of the current source, and thus PWM illumination is commonly installed in society. The light intensity change from off to on states of an LED under PWM driving is literally infinity, which causes the lighting to flicker. The lighting flicker induces not only an optical illusion but also biological effects, including serious health problems, which can be mitigated by raising the modulation frequency. Because the peak intensity of a PWM illumination can be 100 times that of the average intensity, the indoor solar cell, which has a relatively high series resistance, is expected to underperform. In this paper, the characteristics of a commercial indoor DSSC under PWM illumination are studied. It is found that while PWM illumination at low frequency seriously deteriorates the performance of the DSSC, it recovers at high frequency. The latter feature is not found in indoor amorphous-Si solar cells, and the electrochemical impedance spectroscopy revealed that it stems from the electrochemical nature of some components of the series impedance in the DSSC, offering a key piece of evidence of the superiority for use in the modern indoor application of the DSSC over traditional amorphous-Si solar cells.
Journal Article
Synthesis of Linear Black Gold Nanostructures Processable as Sunlight and Low‐Energy Light Collecting Films for Photo‐Thermoelectricity
As one of the effort to cope with the energy crisis and carbon neutrality, utilization of low‐grade energy generated indoors (e.g., light) is imperative because this saves building and house energy, which accounts for ≈40% of total energy consumption. Although photovoltaic devices could contribute to energy savings, it is also necessary to harvest heat from indoor lights to generate electricity because the light absorbed by materials is mostly transformed into heat. For daily life uses, materials should not only have high absorptance and low emittance but also be easily processed into various forms. To this end, this work synthesizes black aqueous suspensions containing winding and bent linear gold nanostructures with diameters of 3–5 nm and length‐to‐diameter ratios of ≈4–10. Their optical and photo‐thermal characteristics are understood through experimental and theoretical investigations. Black gold nanostructures are conveniently processed into metal‐dielectric films on metal, glass, and flexible substrates. The film on copper has an absorptance of 0.97 and an emittance of 0.08. Under simulated sunlight and indoor LED light illumination, the film has equivalent photo‐thermal and photo‐thermoelectric performances to a top‐tier sunlight‐collecting film. This work attempts to modify the film structure to generate more usable electricity from low‐energy indoor light. Black aqueous suspensions containing winding and bent linear gold nanostructures are synthesized to prepare various light collecting films (with high absorptance and low emittance) for the production of photo‐thermoelectricty under the sunlight and low‐energy‐light illumination. Particularly, utilization of heats produced from low‐energy lights could save building energy, hence deal with the energy crisis and carbon neutrality.
Journal Article
Focus on quantum efficiency
Technologies which convert light into energy, and vice versa, rely on complex, microscopic transport processes in the condensed phase, which obey the laws of quantum mechanics, but hitherto lack systematic analysis and modeling. Given our much improved understanding of multicomponent, disordered, highly structured, open quantum systems, this 'focus on' collection collects cutting-edge research on theoretical and experimental aspects of quantum transport in truly complex systems as defined, e.g., by the macromolecular functional complexes at the heart of photosynthesis, by organic quantum wires, or even photovoltaic devices. To what extent microscopic quantum coherence effects can (be made to) impact on macroscopic transport behavior is an equally challenging and controversial question, and this 'focus on' collection provides a setting for the present state of affairs, as well as for the 'quantum opportunities' on the horizon.
Journal Article
Start-up circuit for low-power indoor light energy harvesting applications
A start-up circuit, used in a micro-power indoor light energy harvesting system, is described. This start-up circuit achieves two goals: first, to produce a reset signal, power-on-reset (POR), for the energy harvesting system, and secondly, to temporarily shunt the output of the photovoltaic (PV) cells, to the output node of the system, which is connected to a capacitor. This capacitor is charged to a suitable value, so that a voltage step-up converter starts operating, thus increasing the output voltage to a larger value than the one provided by the PV cells. A prototype of the circuit was manufactured in a 130 nm CMOS technology, occupying an area of only 0.019 mm2. Experimental results demonstrate the correct operation of the circuit, being able to correctly start-up the system, even when having an input as low as 390 mV using, in this case, an estimated energy of only 5.3 pJ to produce the start-up.
Journal Article
Synthesis of Doped g‐C3N4 Photonic Crystals for Enhanced Light‐Driven Hydrogen Production from Catalytic Water‐Splitting
Dopants are frequently used to improve graphitic carbon nitride (gCN) photoactivity. As a doping source, phosphomolybdic acid (PMA) can activate doping sites inside the gCN lattice, resulting in 2D Mo:P‐gCN porous material. However, the gradual loading of the PMA fraction has no systematic improvement in the Mo:P‐gCN photoactivity. For improving the optoelectronic properties of Mo:P‐gCN, its textural geometry is a controllable parameter that can provide enhanced photonic properties, achievable by shaping its morphology through a crystalline template structure, namely, photonic crystals (PCs). Herein, a doped PC material is made of Mo:P‐gCN and PCs and labeled as Mo:P‐gCN/PCs. The impact of PCs is highlighted in the structural, electronic, and optical performances of Mo:P‐gCN. A well‐defined 3D crystalline network is evidenced by microscopic measurements (scanning electron microscopy, AFM, focused ion beam). Mo:P‐gCN/PCs shows a hydrogen production rate (750 μmol g−1 h−1) one time higher than Mo:P‐gCN and 6 times higher than pure gCN. The synthesis strategy proposed in this work leads simultaneously to the Mo:P codoping effect provided by PMA and the slow photon effect due to the PC structure, offering a novel strategy to improve the gCN photoactivity by simultaneously applying polyoxometalates as modifiers and polystyrene opals as templates. Combining the enhanced electronic properties of Mo:P‐doped graphitic carbon nitride (gCN) with the photonic bandgap properties of photonic crystals (PCs) can significantly enhance light harvesting. The fabrication of a PC material out of Mo:P‐doped gCN is a new approach to improve the photocatalytic performance of gCN, which enables efficient light harvesting and charge separation in (photo‐)electrocatalytic sunlight energy conversion.
Journal Article