Decrease In Quantum Efficiency Research Articles

Achieving the conversion from Room-Temperature phosphorescence to photothermal properties by Carbon-Regulated bandgap

Bandgap tunability plays an important role in controlling the photophysical properties of semiconductor material. In this work, we propose a powerful carbon component engineering strategy for regulating the optical bandgap of scandium/cysteine functional materials (Sc/Cys-FMs) that are synthesized by a facile one-pot hydrothermal method. The band structure of Sc/Cys-FMs is closely related to the Cys ligands. As Cys amount rises, the obtained Sc/Cys-FMs exhibit the red-shifted room-temperature phosphorescence (RTP) emission from Sc/Cys-FMs-50 (3.01 eV) to Sc/Cys-FMs-150 (2.14 eV), accompanied by a decrease in quantum efficiency and an increase in lifetime. Meanwhile, the Sc/Cys-FMs show a unique time-dependent phosphorescence color (TDPC) phenomenon, with a dynamic transition of RTP color from yellow to green as the decay time prolongs because of the emission-dependent lifetime. As the amount of Cys further increases, the bandgap can be continuously reduced to 1.88 eV (Sc/Cys-FMs-300) and 1.56 eV (Sc/Cys-FMs-600), causing the quenching of RTP emission and significantly enhanced photothermal properties. The continuously decreasing bandgap has been proven to be directly ascribed to the increase of carbon component in Sc/Cys-FMs. Considering the TDPC properties, Sc/Cys-FMs can be well used for dynamic phosphorescent anti-counterfeiting. This work not only develops a scalable method for preparing functional materials with superior RTP and photothermal properties, but also proposes the carbon component engineering strategy to achieve bandgap tunability of materials.

Temperature-Dependent Efficiency Droop in GaN-Based Blue Micro Light-Emitting Diodes

This work investigates the size-dependent decrease in external quantum efficiency (EQE) of various InGaN/GaN multiple-quantum-well flip-chip blue micro light-emitting diodes (μ-LEDs) of sizes from 10 × 10 μm2 to 250 × 250 μm2 and proposes that the temperature-dependent efficiency droop is the main mechanism for decrease in EQE with reducing dimensions for well-passivated μ-LEDs. Experimental results show that the EQE increases with reducing μ-LED sizes to 50 × 50 μm2. However, the EQE decreases as the μ-LED size is further reduced to 10 × 10 μm2. The measured current-voltage characteristics, the minimum ideality factor, the light-emission patterns by the photon-emission microscope, and the transmission-electron-microscopy images consistently reveal that the decreased EQE of the smallest sized μ-LED is not due to the sidewall leakage: the decreased EQE is rather caused by the temperature-dependent efficiency droop (T-droop), which is systematically found by investigating the blueshift in peak emission wavelength and calculating the thermal resistance (Rth) that increases with the reduced mesa area. The decrease in peak EQE at 440 K compared to 300 K is also presented, which demonstrates that the reduction in peak EQE increases with reducing μ-LED sizes. It is pointed out that the small-sized μ-LEDs suffer from higher junction temperature due to lower heat dissipation caused by higher Rth compared to large-sized μ-LEDs.

3.5 × 3.5 μm2 GaN blue micro-light-emitting diodes with negligible sidewall surface nonradiative recombination

Micro-light-emitting diode displays are generating considerable interest as a promising technology for augmented-reality glasses. However, the fabrication of highly efficient and ultra-small ( <3 μm) micro-light-emitting diodes, which are required for augmented-reality applications, remains a major technical challenge due to the presence of strong sidewall nonradiative recombination. In this study, we demonstrate a 3.5 × 3.5 μm2 blue GaN micro-light-emitting diode with negligible sidewall nonradiative recombination compared with bulk nonradiative recombination. We achieve this by using an ultralow-damage dry etching technique, known as neutral beam etching, to create the micro-light-emitting diode mesa. Our 3.5 × 3.5 μm2 micro-light-emitting diode exhibits a low decrease in external quantum efficiency of only 26% at a current density of 0.01 A/cm2, compared with the maximum external quantum efficiency that is reached at the current density of ∼3 A/cm2. Our findings represent a significant step towards realizing micro-light-emitting diode displays for augmented-reality glasses.

Nanorod length-dependent photodriven H2 production in 1D CdS-Pt heterostructures.

Colloidal quantum confined semiconductor-metal heterostructures are promising candidates for solar energy conversion because their light absorbing semiconductor and catalytic components can be independently tuned and optimized. Although the light-to-hydrogen efficiencies of such systems have shown interesting dependences on the morphologies of the semiconductor and metal domains, the mechanisms of such dependences are poorly understood. Here, we use Pt tipped 0D CdS quantum dots (with ∼4.6nm diameter) and 1D CdS nanorods (of ∼13.8, 27.8, 66.6, and 88.9nm average rod lengths) as a model system to study the distance-dependence of charge separation and charge recombination times and their impacts on photo-driven H2 production. The H2 generation quantum efficiency increases from 0.2% ± 0.0% in quantum dots to 28.9% ± 0.4% at a rod length of 28nm and shows negligible changes at longer rod lengths. The half-life time of electron transfer from CdS to Pt increases monotonically with rod length, from 0.7 ± 0.1 in quantum dots to 170.2 ± 29.5ps in the longest rods, corresponding to a slight decrease in electron transfer quantum efficiency from 92% to 81%. The amplitude-weighted average lifetime of charge recombination of the electron in Pt with the hole in CdS increases from 4.7 ± 0.4 µs in quantum dots to 149 ± 34 µs in 28nm nanorods, and the lifetime does not increase further in longer rods, resembling the trend in the observed H2 generation quantum efficiency. Our result suggests that the competition of the charge recombination process with the hole removal by the sacrificial electron donor plays a dominant role in the observed nanorod length dependent overall light driven H2 generation quantum efficiency.

Raman scattering, absorption and luminescence spectroscopy of CoSiF6·6H2O crystal and CoSiF6·6H2O:Mn4+ red-emitting phosphor

CoSiF6·6H2O and CoSiF6·6H2O:Mn4+ crystals were investigated by means of Raman, optical absorption, and luminescence spectroscopy. Absorption spectra of CoSiF6·6H2O are analyzed by Tanabe-Sugano technique and are proved to be well-describable at crystal field strength Dq = 1000 cm−1, and Racah parameters B = 896 cm−1, C = 4408 cm−1, Dq/B = 1.116. Raman spectroscopy reveals a phase transition associated with the ordering of both the CoO6 and SiF6 octahedra, which occurs through the ordering of the H2O subsystem. Luminescence spectrum of Mn4+ ions in CoSiF6·6H2O lattice consists of six components corresponding to Stokes and anti-Stokes emission from 2E state of Mn4+ ion at vibrational frequencies of MnF6 octahedron ν6 = 230 cm−1, ν4 = 335 cm−1, and ν3 = 645 cm−1. Quantum efficiency of red emission maximizes at excitation wavelength 357 nm and equals to 5%. Decrease of quantum efficiency in comparison to other related materials is explained by absorption of Co2+ ions and non-radiative relaxation in the Co2+ subsystem.

Influence of Mn2+ and Eu3+ Concentration on Photoluminescence and Thermal Stability Properties in Eu3+-Activated ZnMoO4 Red Phosphor Materials.

The integration of trivalent europium ion (Eu3+)-doped zinc molybdate (ZnMoO4) as red phosphors in next-generation solid-state lighting (SSL) is impeded by their extended electron lifetime and suboptimal thermal stability. To overcome these limitations, we propose a co-doping approach by incorporating Mn2+ and Eu3+ in ZnMoO4, aiming to improve thermal reversibility and reduce the lifetime of electron transitions. A series of Eu3+-doped ZnMoO4 and Mn2+/Eu3+-co-doped ZnMoO4 phosphor materials were synthesized via the conventional sol-gel method, and their photoluminescence properties were compared under high-temperature conditions. Experimental results indicate that the introduction of Mn2+ into Eu3+-doped ZnMoO4 leads to a decrease in quantum efficiency and electron lifetime, primarily attributed to defects within the crystal lattice and energy transfer from Eu3+ to Mn2+, resulting in enhanced non-radiative transitions. However, the addition of a small quantity of Mn2+ remarkably improves the thermal stability and reversibility of the phosphors. Consequently, this co-doping strategy presents a promising avenue for expanding the application possibilities of phosphor materials, particularly for high-power SSL applications subjected to elevated temperatures. Hence, Eu3+-only doped samples are well-suited for lighting applications due to their high IQE and excellent thermal stability. Conversely, Eu3+/Mn2+-co-doped samples show promise in applications that require a shorter electron lifetime and good reversibility.

Proton irradiation effects on GaInP/GaAs/Ge triple junction cells

GaAs solar cells, with a higher transfer efficiency, is regarded as a good candidate for the space applications. For the better applications to the deep space exploration, it is necessary to explore its irradiation effects. Here, the effects of irradiation energy and irradiation fluence on the degradation of solar cells were studied, and the results show that proton irradiation with a fluence of 5 × 1011/cm2 has slightly effect on the performance the cell, with further increasing fluence the quantum efficiency decreases; and the degradation of quantum efficiency is manly from long wavelength band, meaning that the displacement damage mainly occurs in middle-junction GaAs cells under relatively higher fluence of proton irradiation. In comparison with the irradiation fluence, the effects of the irradiation energy on the degradation to GaInP cell and GaAs sub-cell are relatively weaker. Non-ionizing energy loss and TCAD simulations were carried out to explain the mechanism behind.

Photosynthetic and Antioxidant Responses of Gymnocarpos przewalskii to Simulated Rainfall Changes

Gymnocarpos przewalskii is a rare Tertiary relict species, mainly distributed in desert areas of northwestern China. Changes in rainfall have a significant impact on the physiological characteristics of desert plants. In the present study, the effects of five simulated rainfall levels on the gas exchange parameters, chlorophyll fluorescence characteristics, and antioxidant system of G. przewalskii were studied. The results show that with increased rainfall the net photosynthetic rate (Pn) and transpiration rate increase significantly. The reduction in Pn is caused by stomatal and non-stomatal limitations under decreased rainfall. Decreased rainfall markedly improves the instantaneous water-use efficiency of leaves. With increased rainfall, the maximum photosynthetic rate, apparent quantum efficiency, and light utilization range significantly increase. Under reduced rainfall, the chlorophyll content, maximum photochemical efficiency of PSII, and steady-state optical quantum efficiency decrease and photoinhibition is caused in the PSII system. A rainfall reduction of 30% leads to massive production of superoxide anions and hydrogen peroxide, causing obvious peroxidation damage. Meanwhile, superoxide dismutase, peroxidase, and catalase in the leaves are significantly enhanced to remove excess reactive oxygen species and alleviate the injury to photosynthetic apparatus. Our study reveals the effect of rainfall changes on the photosynthetic characteristics and antioxidant system of G. przewalskii, and can improve understanding of the adaptive strategies of desert plants under future precipitation changes in northwestern China.

Rugged bialkali photocathodes encapsulated with graphene and thin metal film

Protection of free-electron sources has been technically challenging due to lack of materials that transmit electrons while preventing corrosive gas molecules. Two-dimensional materials uniquely possess both of required properties. Here, we report three orders of magnitude increase in active pressure and factor of two enhancement in the lifetime of high quantum efficiency (QE) bialkali photocathodes (cesium potassium antimonide (CsK2Sb)) by encapsulating them in graphene and thin nickel (Ni) film. The photoelectrons were extracted through the graphene protection layer in a reflection mode, and we achieved QE of ~ 0.17% at ~ 3.4 eV, 1/e lifetime of 188 h with average current of 8.6 nA under continuous illumination, and no decrease of QE at the pressure of as high as ~ 1 × 10–3 Pa. In comparison, the QE decreased drastically at 10–6 Pa for bare, non-protected CsK2Sb photocathodes and their 1/e lifetime under continuous illumination was ~ 48 h. We attributed the improvements to the gas impermeability and photoelectron transparency of graphene.

2 MeV proton irradiation effect on the performance of InAs/GaSb type-II superlattice long-wave infrared detectors.

In this work, we investigated the effect of 2 MeV proton irradiation on the performance of InAs/GaSb type-II superlattice long-wave infrared detectors by combining ground-based irradiation experiments with Stopping and Range of Ions in Matter (SRIM) computer simulations. We found that irradiation with 2 MeV protons significantly increases the dark current density of the detector by more than two orders of magnitude. At the same time, the quantum efficiency decreases by an order of magnitude. Moreover, proton irradiation degrades the device's performance by raising bulk and surface leakage currents. As the mesa size of the device increases, the proportion of surface leakage current in the total dark current drops. When the mesa size is smaller, the detector irradiation damage is greater. In addition, simulations indicate that the amount of damage produced by 2 MeV proton irradiation rises as irradiation fluences increase. The trends of the irradiation damage produced by the SRIM simulation results and the photocurrent measurements after proton irradiation are consistent, whereas the dark current measurements are identical only at small fluences.

Near infrared voltage sensitive dyes based on chromene electron donors.

Excellent hemicyanine voltage sensitive dyes (VSDs) are available for optical electrophysiology over a wide spectral range out to the far red. Near infrared fluorescent VSDs would be advantageous because they allow deeper light penetration into tissue because of decreased light scattering and also because they can be used in combination with other fluorescent indicators or optogenetic actuators. The usual approach to constructing long wavelength chromophores is to lengthen the π-system; however, this is generally accompanied by a significant decrease in fluorescence quantum efficiency and can also decrease aqueous solubility, making it difficult to deliver the probes to the target tissue. The VSDs developed in our lab are generally composed of an amino-naphthyl electron donor moiety linked to a pyridinium acceptor. Here we show that replacing the naphthalene with chromene induces a 60-80 nm red-shift in the absorption and emission spectra while maintaining the structure at the same size and fluorescence quantum yield at the same level. The voltage sensitivity of these chromene-based VSDs is also comparable to our older VSDs and they display opposite polarity sensitivity when excited at the short and long wavelength edges of the absorbance spectra; thus they can be used in dual wavelength ratio measurements to eliminate artifacts from motion and bleaching. We have tested one of these VSDs in voltage imaging of a whole murine heart at 730 nm, by far the longest wavelength reported in voltage imaging. It resolves action potentials in single sweep scans with 10.1% ΔF/F per action potential. Chromene-based electron donors are likely to find wide applications in generating long wavelength hemicyanines or cyanines. (Supported by NIH grant MH116830. Conflict of Interest statement: LML, CDA, and PY are founders and owners of Potentiometric Probes LLC.)

Solvent Effect on the spectral and photophysical properties of the Acridone

UV/Vis absorption, emission, and excitation spectroscopy with various solvents (dimethyl sulfoxide (DMSO), N,N-Dimethylformamide (DMF), and tetrahydrofuran (THF) and Acetone) at two concentrations (10−4 and 10−5) Mol/L were used to investigate the spectra and photophysical properties of Acridone. Using the integrated emission spectra, the fluorescence quantum yields are calculated. The emission maxima were determined using the red absorption band’s positions and bandwidths. The maximum absorption and emission wavelengths were found to be 390–399 nm and 399–413 nm, respectively, resulting in Stokes shifts of 318.05 and 1142.62 cm-1. Fluorescence spectra have a broad spectral range so that as concentration is increased, each peak shifts toward a long wavelength. It has been discovered that as concentrations increase, the quantum efficiency decreases. The fluorescence quantum yield magnitude is affected by solvents, with THF having the highest value.

COULD FULL SUN EXPOSURE REPRESENT PHYSIOLOGICAL ADVANTAGES FOR CRIOLLO COCOA CULTIVATION?

In Venezuela, the physiological performance of adult cocoa trees under full sun exposure is unknown. The long-term effect of high photon flux density (PFD) on leaf water potential (), leaf area index (LAI), gas exchange, photochemical activity of PSII, and photosynthetic pigment content in adult cocoa trees of Ocumare 61 (OC-61) was evaluated, in order to know if OC-61 could have a good photosynthetic performance in plants grown in full sun (E) or if on the contrary there is a physiological disadvantage compared to those grown in shade (S), self-shaded leaves were also evaluated in each condition (E+A and S+A). The OC-61 clone grown in E showed significant changes in some physiological traits: lower , lower IAF, higher rates of photosynthesis (A) and water use efficiency (WUE), lower intercellular CO2 concentration (Ci) and lower total chlorophyll, and carotenoid content. An increase in electron transport rate, PSII quantum efficiency, photochemical and non-photochemical extinction coefficient was found that would partially explain the higher A's in E; there was no decrease in maximum quantum efficiency indicating the absence of photoinhibition. Clone OC-61 is a shade tolerant crop; however, the results indicate that it can be acclimatized to high sun exposure without damage to PSII functioning, which could represent a physiological advantage for clone OC-61 grown in the study area.

Atomistic analysis of Auger recombination in c -plane (In,Ga)N/GaN quantum wells: Temperature-dependent competition between radiative and nonradiative recombination

We present an atomistic theoretical study of the temperature dependence of the competition between Auger and radiative recombination in $c$-plane (In,Ga)N/GaN quantum wells with indium (In) contents of 10%, 15%, and 25%. The model accounts for random alloy fluctuations and the connected fluctuations in strain and built-in field. Our investigations reveal that the total Auger recombination rate exhibits a weak temperature dependence; at a temperature of 300 K and a carrier density of ${n}_{3D}=3.8\ifmmode\times\else\texttimes\fi{}{10}^{18}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$, we find total Auger coefficients in the range of $\ensuremath{\approx}6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}30}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{6}/\mathrm{s}$ (10% In) to $\ensuremath{\approx}3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}31}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{6}/\mathrm{s}$ (25% In), thus large enough to significantly impact the efficiency in (In,Ga)N systems. Our calculations show that the hole-hole-electron Auger rate dominates the total rate for the three In contents studied; however, the relative difference between the hole-hole-electron and electron-electron-hole contributions decreases as the In content is increased to 25%. Our studies provide further insight into the origin of the ``thermal droop'' (i.e., the decrease in internal quantum efficiency with increasing temperature at a fixed carrier density) in (In,Ga)N-based light-emitting diodes. We find that the ratio of radiative to nonradiative (Auger) recombination increases in the temperature range relevant to the thermal droop ($\ensuremath{\ge}300$ K), suggesting that the competition between these processes is not driving this droop effect in $c$-plane (In,Ga)N/GaN quantum wells. This finding is in line with recent experimental studies.

Perovskite light-emitting diodes

Light-emitting diodes based on halide perovskites have undergone rapid development in recent years and can now offer external quantum efficiencies of over 23%. However, the practical application of such devices is still limited by a number of factors, including the poor efficiency of blue-emitting devices, difficulty in accessing emission wavelengths above 800 nm, a decrease in external quantum efficiency at high current density, a lack of understanding of the effect of the electric field on mobile ions present in the perovskite materials, and short device lifetimes. Here we review the development of perovskite light-emitting diodes. We examine the key challenges involved in creating efficient and stable devices, and consider methods to alleviate the poor efficiency of blue-emitting devices, leverage emission in the long infrared region and create spin-polarized light-emitting diodes. This Review examines the development of perovskite light-emitting diodes, exploring the key challenges involved in creating efficient and stable devices.

Pre-Acclimation to Elevated Temperature Stabilizes the Activity of Photosystem I in Wheat Plants Exposed to an Episode of Severe Heat Stress.

The importance of high temperature as an environmental factor is growing in proportion to deepening global climate change. The study aims to evaluate the effects of long-term acclimation of plants to elevated temperature on the tolerance of their photosynthetic apparatus to heat stress. Three wheat (Triticum sp. L.) genotypes differing in leaf and photosynthetic traits were analyzed: Thesee, Roter Samtiger Kolbenweizen, and ANK 32A. The pot experiment was established in natural conditions outdoors (non-acclimated variant), from which a part of the plants was placed in foil tunnel with elevated temperature for 14 days (high temperature-acclimated variant). A severe heat stress screening experiment was induced by an exposition of the plans in a growth chamber with artificial light and air temperature up to 45 °C for ~12 h before the measurements. The measurements of leaf photosynthetic CO2 assimilation, stomatal conductance, and rapid kinetics of chlorophyll a fluorescence was performed. The results confirmed that a high temperature drastically reduced the photosynthetic assimilation rate caused by the non-stomatal (biochemical) limitation of photosynthetic processes. On the other hand, the chlorophyll fluorescence indicated only a moderate level of decrease of quantum efficiency of photosystem (PS) II (Fv/Fm parameter), indicating mostly reversible heat stress effects. The heat stress led to a decrease in the number of active PS II reaction centers (RC/ABS) and overall activity o PSII (PIabs) in all genotypes, whereas the PS I (parameter ψREo) was negatively influenced by heat stress in the non-acclimated variant only. Our results showed that the genotypes differ in acclimation capacity to heat stress, and rapid noninvasive techniques may help screen the stress effects and identify more tolerant crop genotypes. The acclimation was demonstrated more at the PS I level, which may be associated with the upregulation of alternative photosynthetic electron transport pathways with clearly protective functions.

Photon-induced degradation of InGaN-based LED in open-circuit conditions investigated by steady-state photocapacitance and photoluminescence

Degradation of InGaN–GaN LEDs has been the subject of intense investigations in the past few years. While current- and temperature-induced degradation processes have been described, the impact of photon-induced degradation has not been investigated in detail in the literature. This paper aims at improving the understanding of the mechanisms responsible for the degradation of the InGaN subject to high photon densities by stressing the devices under a high-intensity laser beam in open-circuit conditions (i.e., in the absence of external current). We analyzed the degradation by means of electrical, optical, and deep-level characterization techniques. First, we demonstrate the existence of optically induced degradation processes in GaN LEDs: from photoluminescence measurements, we observed a decrease in the luminescence after stress, more prominent in the region irradiated during stress. Second, we ascribe this effect to a decrease in internal quantum efficiency due to the generation of non-radiative defects within the active region. Third, by steady-state photocapacitance measurements, we reveal the presence of a shallow level with an energy of EC–2.2 eV, which can be ascribed to gallium vacancies and its complexes with oxygen and nitrogen and can be related to the increase in yellow luminescence.

Salt Stress Affects Plastid Ultrastructure and Photosynthetic Activity but Not the Essential Oil Composition in Spearmint (Mentha spicata L. var. crispa "Moroccan").

High levels of soil salinity affect plant growth, reproduction, water and ion uptake, and plant metabolism in a complex manner. In this work, the effect of salt stress on vegetative growth, photosynthetic activity, and chloroplast ultrastructure of spearmint (Mentha spicata L. var. crispa “Moroccan”) was investigated. After 2 weeks of low concentration treatments (5, 25, and 50 mM NaCl) of freshly cut shoots, we observed that the stem-derived adventitious root formation, which is a major mean for vegetative reproduction among mints, was completely inhibited at 50 mM NaCl concentration. One-week-long, high concentration (150 mM NaCl) salt stress, and isosmotic polyethylene glycol (PEG) 6000 treatments were compared in intact (rooted) plants and freshly cut, i.e., rootless shoots. Our data showed that roots have an important role in mitigating the deleterious effects of both the osmotic (PEG treatment) and specific ionic components of high salinity stress. At 50 mM NaCl or above, the ionic component of salt stress caused strong and irreversible physiological alterations. The effects include a decrease in relative water content, the maximal and actual quantum efficiency of photosystem II, relative chlorophyll content, as well as disorganization of the native chlorophyll-protein complexes as revealed by 77 K fluorescence spectroscopy. In addition, important ultrastructural damage was observed by transmission electron microscopy such as the swelling of the thylakoid lumen at 50 mM NaCl treatment. Interestingly, in almost fully dry leaf regions and leaves, granum structure was relatively well retained, however, their disorganization occurred in leaf chloroplasts of rooted spearmint treated with 150 mM NaCl. This loss of granum regularity was also confirmed in the leaves of these plants using small-angle neutron scattering measurements of intact leaves of 150 mM NaCl-stressed rooted plants. At the same time, solid-phase microextraction of spearmint leaves followed by gas chromatography and mass spectrometry (GC/MS) analyses revealed that the essential oil composition of spearmint was unaffected by the treatments applied in this work. Taken together, the used spearmint cultivar tolerates low salinity levels. However, at 50 mM NaCl concentration and above, the ionic components of the stress strongly inhibit adventitious root formation and thus their clonal propagation, and severely damage the photosynthetic apparatus.

Intensity-based and a lifetime-based PSP imaging method with enhanced sensitivity

A pressure-/temperature-sensitive paint (PSP/TSP) has been developed and used as a measurement tool for the two-dimensional distribution of pressure and temperature on aerodynamic surfaces. In recent years, although the concern with measuring a pressure difference of several Pa, such as countermeasures against the noise of small fans, has been growing, the resolution of current PSP measurements is limited to several 10 Pa, even with carefully conducted measurements. For highly accurate measurements, researches on the advanced coating films in PSP/TSP have eagerly been conducted to date. However, measurement resolution and accuracy deteriorate when quantum efficiency or lifetime decrease under high pressure or high temperature conditions.

Wide variation of winter-induced sustained thermal energy dissipation in conifers: a common-garden study.

Low temperature in winter depresses rates of photosynthesis, which, in evergreen plants, can exacerbate imbalances between light absorption and photochemical light use. Damage that could result from increased excess light absorption is minimized by the conversion of excitation energy to heat in a process known as energy dissipation, which involves the de-epoxidized carotenoids of the xanthophyll cycle. Overwintering evergreens employ sustained forms of energy dissipation observable even after lengthy periods of dark acclimation. Whereas most studies of photoprotective energy dissipation examine one or a small number of species; here, we measured the levels of sustained thermal energy dissipation of seventy conifer taxa growing outdoors under common-garden conditions at the Red Butte Garden in Salt Lake City, Utah, U.S.A. (forty nine taxa were also sampled for needle pigment content). We observed an extremely wide range of wintertime engagement of sustained energy dissipation; the percentage decrease in dark-acclimated photosystem II quantum efficiency from summer to winter ranged from 6 to 95%. Of the many pigment-based parameters measured, the magnitude of the seasonal decrease in quantum efficiency was most closely associated with the seasonal increase in zeaxanthin content expressed on a total chlorophyll basis, which explained only slightly more than one-third of the variation. We did not find evidence for a consistent wintertime decrease in needle chlorophyll content. Thus, the prevailing mechanism for winter decreases in solar-induced fluorescence emitted by evergreen forests may be decreases in fluorescence quantum yield, and wintertime deployment of sustained energy dissipation likely underlies this effect.