Energy Trapping Research Articles

Bi2MoO6/BiFeO3 heterojunction nanofibers: Enhanced photocatalytic activity, charge separation mechanism and magnetic separability

Uniform Bi2MoO6 nanosheets were grown in a high dispersed fashion on electrospun BiFeO3 nanofibers via a solvothermal technique. The loading amount of Bi2MoO6 in the Bi2MoO6/BiFeO3 heterojunction nanofibers could be controlled by adjusting the precursor concentrations in the solvothermal process. The XPS analysis, energy band position calculation and trapping experiments all proved that the Bi2MoO6/BiFeO3 heterojunction is a Z-scheme heterojunction. The Z-scheme Bi2MoO6/BiFeO3 heterojunction had a much higher photocatalytic activity in the visible-light photodegradation of Rhodamine B (RhB) and tetracycline hydrochloride (TC) than pure BiFeO3 nanofibers or pure Bi2MoO6 nanosheets. The enhanced photocatalytic activity was attributed to the formation of Z-scheme Bi2MoO6/BiFeO3 heterojunctions, which could be beneficial to the separation of photogenerated electron-hole pairs. Moreover, the Bi2MoO6/BiFeO3 heterojunction nanofibers could be easily separated under an external magnetic field via the ferromagnetic BiFeO3. After several cycles, the photocatalytic activity of the Bi2MoO6/BiFeO3 heterojunction no longer significantly decreased suggesting that the Bi2MoO6/BiFeO3 heterojunction is stable. These Z-scheme Bi2MoO6/BiFeO3 heterojunction nanofibers with highly visible-light photocatalytic activity, excellent chemical stability and magnetic separability could be useful in many practical applications.

Photonic properties of novel Yb3+ doped germanium-lead oxyfluoride glass-ceramics for laser cooling applications

In recent years, our research group has developed and studied new rare-earth doped materials for the promising technology of solid-state laser cooling, which is based on anti-stokes fluorescence. To the best of our knowledge, our group is the only one in Canada leading the research into the properties of nanoparticles, glasses and glass-ceramics for optical refrigeration applications. In the present work, optical properties of 50GeO2-30PbF2-18PbO-2YbF3 glass-ceramics for laser cooling are presented and discussed as a function of crystallization temperature. Spectroscopic results show that samples have near infrared photoluminescence emission due to the 2F5/2–2F7/2 Yb3+ transition, centered at ~1016 nm with an excitation wavelength of 920 nm or 1011 nm, and the highest photoluminescence emission efficiency occurs for heat-treatment for 5 h at 350°C. The internal photoluminescence quantum yield varies between 99% and 80%, depending on the temperature of heat-treatment, being the most efficient under 1011 nm excitation. The 2F5/2 lifetime increases from 1.472 to 1.970 ms for heat treatments at 330°C to 350°C, respectively, due to energy trapping and the low phonon energy of the nanocrystals. The sample temperature dependence was measured with a fiber Bragg grating sensor, as a function of input pump laser wavelength and processing temperature. These measurements show that the heating process approaches near zero for an excitation wavelength between 1020 and 1030 nm, which is an indication that phonons are removed effectivelly from the glass-ceramic materials, and they can be used for optical laser cooling applications. On the other hand, the temperature increase as a function of input laser power into samples remains constant between 920 and 980 nm wavelength excitation, a temperature variation of 36 K/W (temperature of 58°C/W) was attained under excitation at 950 nm, showing a possible use for biomedical applications to be explored.1)

Regulation of excitation energy in Nannochloropsis photosystem II.

Recently, we isolated a complex consisting of photosystem II (PSII) and light-harvesting complexes (LHCs) from Nannochloropsis granulata (Umetani et al. Photosynth Res 136:49-61, 2017). This complex contained stress-related protein, Lhcx, as a major component of LHC (Protein ID is Naga_100173g12.1), suggesting that non-photochemical quenching activities may be taking place in the PSII-LHC complex. In this study, we examined the energy transfer dynamics in the isolated LHCs and PSII-LHC complexes, and found substantial quenching capacity. In addition, the LHCs contained low-energy chlorophylls with fluorescence maxima at approximately 710nm, which may enhance the quenching efficiency in the PSII-LHC. Delayed fluorescence analysis suggested that there was an approximately 50% reduction in energy trapping at the PSII reaction center in the PSII-LHC supercomplex under low-pH condition compared to neutral pH condition. Enhanced quenching may confer a survival advantage in the shallow-water habitat of Nannochloropsis.

A possible molecular basis for photoprotection in the minor antenna proteins of plants

The bioenergetics of light-harvesting by photosynthetic antenna proteins in higher plants is well understood. However, investigation into the regulatory non-photochemical quenching (NPQ) mechanism, which dissipates excess energy in high light, has led to several conflicting models. It is generally accepted that the major photosystem II antenna protein, LHCII, is the site of NPQ, although the minor antenna complexes (CP24/26/29) are also proposed as alternative/additional NPQ sites. LHCII crystals were shown to exhibit the short excitation lifetime and several spectral signatures of the quenched state. Subsequent structure-based models showed that this quenching could be explained by slow energy trapping by the carotenoids, in line with one of the proposed models. Using Fluorescence Lifetime Imaging Microscopy (FLIM) we show that the crystal structure of CP29 corresponds to a strongly quenched conformation. Using a structure-based theoretical model we show that this quenching may be explained by the same slow, carotenoid-mediated quenching mechanism present in LHCII crystals.

Coupling Vibration Analysis of Trapped-Energy Rectangular Quartz Resonators by Variational Formulation of Mindlin's Theory.

Mindlin’s two-dimensional theory has been derived and applied to research on quartz resonators for a long time. However, most works have focused on vibrations varying only in two directions, including thickness direction, while the effect of other directions like the length or width direction is normally neglected. Besides, researchers often model quartz resonators as fully electroded plates because of the resulting simplicity. Since a real device is finite in all directions and is only centrally electroded, results obtained in such works cannot offer quantitative information on vibrations with enough accuracy. In this paper, a theoretical analysis of a rectangular trapped-energy resonator of AT-cut quartz is studied using the Ritz method, associated with the variational formulation of Mindlin’s first-order equations. Frequency spectra and mode shapes of a real-scaled trapped-energy resonator, which is finite in all directions, are obtained with the consideration of mode couplings among thickness-shear mode, thickness-twist mode, and flexural mode. Results show the existence of an energy-trapping and coupling phenomenon and are helpful for thorough and accurate understanding of quartz resonator vibrations. Detailed discussions on the effects of structural parameters on mode couplings and energy trapping are provided, and the results can helpfully guide the selection of aspect ratio, length/thickness ratio, and electrode inertia in device design.

Analysis on vibration energy concentration of the one-dimensional wedge-shaped acoustic black hole structure

The transverse vibration energy of a plate with a wedge-shaped profile can be trapped by acoustic black hole effect to its edge portion, in case the wedge thickness is diminished according to the power-law h( x) = εxm with m ≥ 2.0. The acoustic black hole effect exhibits potential ability for passive vibration control and energy harvesting. In this article, the transfer matrix method is adopted to establish and solve the dynamical model of acoustic black hole structure. Energy ratio is defined as a ratio of the energy trapped within the edge portion to that of the whole wedge, to illustrate the energy concentration effect. Analyses show that both the strain energy ratio and kinetic energy ratio of the acoustic black hole structure achieve the minimum when the wedge is in resonances, although these two kinds of energy come to peaks at this case. However, in the case of small length of the edge portion, the strain energy ratio reaches the highest peaks at the second and higher resonances, rather than at the first one. Generally, the best effect of energy concentration occurs when m ranges from 2.5 to 3.0. Reducing the truncation thickness and increasing the maximum height can improve the energy trapping.

Improved photosynthetic efficacy of maize (Zea mays) plants with arbuscular mycorrhizal fungi (AMF) under high temperature stress

In this study, pot experiments were performed to investigate the effects of high temperature stress (44 °C) in maize plants colonized with and without arbuscular mycorrhizal fungi (AMF). Various parameters characterizing photosynthetic activity were measured in order to estimate the photosynthetic efficiency in maize plants. It was observed that density of active reaction centers of PSII, quantum efficiency of photosystem II (PSII), linear electron transport, excitation energy trapping, performance index, net photosynthesis rate increased in AMF (+) plants at 44 °C ± 0.2 °C. Efficiency of primary photochemical reaction (represented as Fv/Fo) increased in AMF (+) plants as compared to AMF (−) plants. AMF seems to have protected water splitting complex followed by enhanced primary photochemistry of PSII under high temperature. Basic morphological parameters like leaf width, plant height and cob number increased in AMF (+) plants as compared to AMF (−) plants. AMF (+) plants grew faster than AMF (−) plants due to larger root systems. Chl content increased in AMF (+) plants as compared to AMF (−) maize plants. AMF hyphae likely increased Mg uptake which in turn increased the total chlorophyll content in AMF (+) maize plants. This subsequently led to a higher production in photosynthate and biomass. Thus AMF (+) plants have shown better photosynthesis performance as compared to AMF (−) maize plants under high temperature stress.

Adapting Three Classic Demonstrations To Teach Radiant Energy Trapping and Transfer As Related to the Greenhouse Effect

Three concepts necessary for understanding the greenhouse effect are infrared radiation, absorption of infrared radiation by greenhouse gases, and steady-state energy flow. Herein, we describe adaptations to three classic demonstrations for teaching these concepts. William Hershel’s discovery of infrared radiation has been adapted into a fast and reliable demonstration using a pyranometer. We provide guidelines for building a ball-and-spring model of carbon dioxide that demonstrates the absorption of IR and the three fundamental vibrational modes of carbon dioxide and their relative frequencies. Finally, we describe an adaptation of Blanck’s plastic water-flow device to demonstrate how adding greenhouse gases can alter the steady-state flow of energy through the atmosphere.

The phycobilisome terminal emitter transfers its energy with a rate of (20 ps)\u20131 to photosystem II

Ultrafast time resolved emission spectra were measured in whole cells of a PSI-deficient mutant of Synechocystis sp. PCC 6803 at room temperature and at 77K to study excitation energy transfer and trapping. By means of a target analysis it was estimated that the terminal emitter of the phycobilisome, termed allophycocyanin 680, transfers its energy with a rate of (20 ps)–1 to PSII. This is faster than the intraphycobilisome energy transfer rates between a rod and a core cylinder, or between the core cylinders.

A Physical Model for Metal–Oxide Thin-Film Transistor Under Gate-Bias and Illumination Stress

A negative shift in the turn-on voltage of a metal–oxide thin-film transistor under negative gate-bias and illumination stress has been frequently reported. The stretched-exponential equation, predicated largely on a charge-trapping mechanism, has been commonly used to fit the time dependence of the shift. The fitting parameters, some with unsubstantiated physical origin, are extracted by curve fitting. A more physically based model is presently formulated, incorporating the photogeneration, transport, and trapping of holes. The model parameters of generation energy barrier, hole mobility, and trapping time constant are extracted from the measured gate-bias dependent turn-on voltage shift. It is theoretically deduced and experimentally verified that the degradation kinetics is either generation or transport limited. The model can be further applied to explain the attenuated shift under positive bias and illumination stress, if the screening of the electric field emanating from the gate bias is also accounted for. From the effects of asymmetric source/drain bias applied during stress, it is deduced that the trapping is localized along the length of the channel interface. The turn-on voltage of a transistor after such stress is constrained by the portion of the channel exhibiting the smallest shift.

Confining excitation energy of Er3+-sensitized upconversion nanoparticles through introducing various energy trapping centers

Various energy trapping centers are employed to simultaneously suppress concentration quenching and tune luminescence output through efficiently confining the excitation energy in Er3+-sensitized upconversion nanoparticles.

Empirical base solar reflective array accumulator design simulator

Sun energy in Indonesia is 5Kwh/m2/day average per year. This alternative energy can be convert to solar thermal up to 80% efficiency, the percentage is highly significant compare to electric conversion that only has 20%. To provide any process requirement for heating, an empirical research of reflective array accumulator has been done, so that a design simulation for the accumulator has to be held. The accumulator can be used as a heat energy supplier for drying, egg hatching, food oven and other requirement. The sun energy trapping method is a reflective array. This method aims to maximize the energy captured and stored in an accumulator and has to be maintained for 24 hours by opening and closing the array. This simulator will calculated and control some input such as water mass, accumulator temperature, environment temperature, humidity and sun intensity. The array control performance to watch diffuse solar light intensity by time. The result of the simulation will give absorption storage capability, insulation capability to watch sun energy performance per day. It is expected that with the simulation, it can simplify the design of the accumulator and improve the efficiency of heat energy storage. The absorption capability perform 72%.

A novel strategy for markedly enhancing the red upconversion emission in Er3+/Tm3+ cooperated nanoparticles

A novel core–shell structured nanocrystal with energy trapping centers of Tm3+ ions doped in the Er3+-hosted core zone and Yb3+ ions doped in the shell portion is innovated to achieve super-bright red upconversion emission upon low 980 nm laser excitation.

How reduced excitonic coupling enhances light harvesting in the main photosynthetic antennae of diatoms

Strong excitonic interactions are a key design strategy in photosynthetic light harvesting, expanding the spectral cross-section for light absorption and creating considerably faster and more robust excitation energy transfer. These molecular excitons are a direct result of exceptionally densely packed pigments in photosynthetic proteins. The main light-harvesting complexes of diatoms, known as fucoxanthin-chlorophyll proteins (FCPs), are an exception, displaying surprisingly weak excitonic coupling between their chlorophyll (Chl) a's, despite a high pigment density. Here, we show, using single-molecule spectroscopy, that the FCP complexes of Cyclotella meneghiniana switch frequently into stable, strongly emissive states shifted 4-10 nm toward the red. A few percent of isolated FCPa complexes and ∼20% of isolated FCPb complexes, on average, were observed to populate these previously unobserved states, percentages that agree with the steady-state fluorescence spectra of FCP ensembles. Thus, the complexes use their enhanced sensitivity to static disorder to increase their light-harvesting capability in a number of ways. A disordered exciton model based on the structure of the main plant light-harvesting complex explains the red-shifted emission by strong localization of the excitation energy on a single Chl a pigment in the terminal emitter domain due to very specific pigment orientations. We suggest that the specific construction of FCP gives the complex a unique strategy to ensure that its light-harvesting function remains robust in the fluctuating protein environment despite limited excitonic interactions.

Experimental verification of a quasi-trapped degenerate mode magnetic acoustic resonator

This paper presents an elastic resonator exhibiting modal degeneracy and quasi-energy trapping of the displacement field. Electromagnetic acoustic based coupling is employed to excite a pair of degenerate SH dominated modes in an aluminium plate. A circular mesa is machined symmetrically on the plate for the purpose of localising the displacement field. Numerical modelling of the modal properties are compared with experimental measurements. Mapping of the modeshapes using 3D laser vibrometry shows that displacement field to be highly localised to the region defining the mesa in agreement with the numerical model. The numerical model shows that significant out of plane displacement outside the mesa region is expected due to the propagating SV+P waves of the plate. It is expected that design modification will reduce the out of plane contributions thus improving the energy trapping. The high Q-factor of the degenerate trapped resonator has potential applications as a gyroscopic sensor or mass sensor.

Unique Trapped Dimer State of the Photogenerated Hole in Hybrid Orthorhombic CH3NH3PbI3 Perovskite: Identification, Origin, and Implications.

Revealing the innate character and transport of the photogenerated hole is essential to boost the high photovoltaic performance in the lead-based organohalide perovskite. However, knowledge at the atomic level is currently very limited. In this work, we systematically investigate the properties of the photogenerated hole in the orthorhombic CH3NH3PbI3 using hybrid functional PBE0 calculations with spin-orbit coupling included. An unexpected trapping state of the hole, localized as I2- (I dimer), is uncovered, which was never reported in photovoltaic materials. It is shown that this localized configuration is energetically more favorable than that of the delocalized hole state by 191 meV and that it can highly promote the diffusion of the hole with an energy barrier as low as 131 meV. Furthermore, the origin of I dimer formation upon trapping of the hole is rationalized in terms of electronic and geometric effects, and a good linear correlation is found between the hole trapping capacity and the accompanying structural deformation in CH3NH3PbX3 (X = Cl, Br, and I). It is demonstrated that good CH3NH3PbX3 materials for the hole diffusion should have small structural deformation energy and weak hole trapping capacity, which may facilitate the rational screening of superior photovoltaic perovskites.

Peculiarities of energy trapping of the UHF elastic waves in diamond-based piezoelectric layered structure. I. Waveguide criterion

Finite Element Modeling of the peculiarities of the trapping energy phenomenon in application to the piezoelectric layered structure (PLS) “Al/(0 0 1) AlN/Mo/(1 0 0) diamond” has been fulfilled. The resonant properties of longitudinal bulk acoustic waves (BAW) as well as frequency dependence of impedance within the 1 – 6 GHz band have been studied. The investigation of distribution of elastic energy flow and elastic displacements in a PLS cross-section allowed us to obtain an important information on energy trapping (ET) in PLS.Experimentally and as a result of modeling, it has been found that Q minimums are observed in PLS at quarter-wave resonance in the thin-film piezoelectric transducer (TFPT). Maximal Q value was observed at half-wave resonance in TFPT.It has been established that the ET-effect depends considerably on the mutual location of the n-th overtone’s antiresonant frequency fa,n and cut-off frequencies of substrate fs,n−k−1 and fs,n−k where fs,n−k−1<fa,n<fs,n−k, and k=0, 1,2,… is the number of half-length waves to be stowed on the thickness of TFPT. The total violation of the ET-effect will be arisen at the condition f >fs,n−k, when the BAW energy excites the symmetrical or antisymmetrical Lamb waves.

Energy transfer and trapping in Synechococcus WH 7803

Excitation energy transfer (EET) and trapping in Synechococcus WH 7803 whole cells and isolated photosystem I (PSI) complexes have been studied by time-resolved emission spectroscopy at room temperature (RT) and at 77 K. With the help of global and target analysis, the pathways of EET and the charge separation dynamics have been identified. Energy absorbed in the phycobilisome (PB) rods by the abundant phycoerythrin (PE) is funneled to phycocyanin (PC645) and from there to the core that contains allophycocyanin (APC660 and APC680). Intra-PB EET rates have been estimated to range from 11 to 68/ns. It was estimated that at RT, the terminal emitter of the phycobilisome, APC680, transfers its energy at a rate of 90/ns to PSI and at a rate of 50/ns to PSII. At 77 K, the redshifted Chl a states in the PSI core were heterogeneous, with maximum emission at 697 and 707 nm. In 72% of the PSI complexes, the bulk Chl a in equilibrium with F697 decayed with a main trapping lifetime of 39 ps.

Magnetic-control multifunctional acoustic metasurface for reflected wave manipulation at deep subwavelength scale

Acoustic metasurfaces, exhibiting superior performance with subwavelength thickness, are ideal alternatives for functionalities such as wavefront modulation and acoustic energy trapping, etc. However, most of the reported acoustic metasurfaces were passive. Here a magnetically tuned mechanism is reported for membrane-type acoustic metamaterials. Harnessing the geometric nonlinearity of membrane structures, the transmission spectrum is both theoretically and experimentally tuned over broadband by an external static magnetic force. Simultaneously, the phase profiles can be readily tailored by the magnetic stimulus. Further, a magnetic-control multifunctional metasurface is proposed for low-frequency wave manipulation. By switching the magnetic force distribution, multi extraordinary phenomena, such as acoustic wave redirecting, focusing, bending, etc., are realized without changing the physical structure. Besides, it is demonstrated the proposed metasurface, at deep subwavelength scale (~1/85λ), supports anomalous reflected wave manipulation over a wide band. These results open up new degrees of freedom to steer acoustic wave and pave a way for designing active acoustic devices.

First-principles prediction of interstitial carbon, nitrogen, and oxygen effects on the helium behavior in nickel

The effects of interstitial carbon, nitrogen, and oxygen (C/N/O) on the helium behavior in nickel are studied by using first-principles calculations. The interstitial C/N/O changes the occupying priority of helium to the first nearest neighbor Oct-site, which is related to local strain effect and chemical bonding between helium and its adjacent atoms. Both binding energy calculation and diffusion property analysis confirm that the interstitial C/N/O can trap helium in nickel. Moreover, with lower binding energy and larger trapping radii to helium, the interstitial oxygen has significant effect on helium trapping compared with that of nitrogen and carbon. With more helium aggregating at vacancy, the C/N/O would also trap smaller helium clusters and repel larger ones, indicating that the interstitial C/N/O could disperse helium bubbles and further inhibit their growth in nickel. This work helps to understand the helium embrittlement resistant mechanisms of the initial nucleation sites for second phase nanoparticles in nickel-based alloys.