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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

LHCSR1 Functions as a Dimmer Switch for Light Harvesting

In oxygenic photosynthesis, high light leads to a set of photoprotective processes, known as nonphotochemical quenching, that are required for fitness. In moss and algae, the pigment−protein complex, light-harvesting stress-related (LHCSR), is crucial for photoprotection. Acidification of the thylakoid lumen under high light triggers the activation of LHCSR and the conversion of the xanthophyll violaxanthin into zeaxanthin, which is found within LHCSR. These interrelated molecular components combine to turn on a safety valve that dissipates excess energy as heat. Previous studies of detergent-solubilized LHCSR1 found that pH and zeaxanthin regulate distinct quenching sites via the protein conformation. However, protein function in the native membrane environment can be significantly different. In this work, we applied single-molecule fluorescence spectroscopy to LHCSR1 in membrane nanodiscs. The membrane environment enhanced total quenching, regardless of pH or zeaxanthin-binding. pH-dependent quenching was still observed whereas zeaxanthin-dependent quenching was suppressed. Conformational changes also increased in the membrane, establishing that the local environment can change the nature of the equilibrium between light harvesting and photoprotection.

Hoffmann, Madeline P. [Massachusetts Inst. of Tech↗
DOE OSTI2020

Luminescence Quenching via Deep Defect States: A Recombination Pathway via Oxygen Vacancies in Ce-Doped YAG

Luminescence quenching via nonradiative recombination channels limits the efficiency of optical materials such as phosphors and scintillators and therefore has implications for conversion efficiency and device lifetimes. In materials such as Ce-doped yttrium aluminum garnet (YAG:Ce), quenching shows strong dependence on both temperature and activator concentration, limiting the fabrication of high-intensity white-light emitting diodes with high operating temperatures. Here, we reveal by means of first-principles calculations an efficient recombination mechanism in YAG:Ce that involves oxygen vacancies and gives rise to thermally activated concentration quenching. We demonstrate that the key requirements for this mechanism to be active are localized states with strong electron-phonon coupling. These conditions are commonly found for intrinsic defects such as anion vacancies in wide band gap materials. The present findings are therefore relevant to a broad class of optical materials and shine light on thermal quenching mechanisms in general.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Reduction of Exciton Diffusion Length with Genetically Tuned Non-Photochemical Quenching in Plant Thylakoid Membranes

Non-photochemical quenching (NPQ) protects plants from excess light by dissipating excitation energy as heat. Limited exciton migration is a key feature of NPQ, reducing the energy flux to reaction centers; however, quantitative evidence for this mechanism in native thylakoid membranes has been lacking. Here, we investigate the correlation between NPQ activity and exciton diffusion length (LD) using Nicotiana benthamiana mutants with distinct NPQ capacities. NPQ under both light- and dark-acclimated conditions was quantified for each genotype via fluorescence lifetime snapshots, and exciton mobility was probed using transient absorption spectroscopy with exciton-exciton annihilation analysis. By comparing the relationship between chlorophyll fluorescence lifetime and LD across mutants, we observed that NPQ activation quantitatively limits the spatial range of exciton migration, thereby reducing the access to reaction centers. Our findings provide direct experimental evidence that NPQ modulates the dynamics of energy transport, advancing our understanding of photoprotective regulation in photosynthetic systems.

Diffusion↗
DOE OSTI2022

Modeling ionization quenching in organic scintillators

Ionization quenching models were assessed by evaluating light yield data from multiple organic scintillators and recoil ions over a fission spectrum neutron energy range, important for basic science and applications.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Hidden diversity: Transcriptomic and photosynthetic variation among common ‘wild type’ Chlamydomonas strains

The unicellular green alga Chlamydomonas reinhardtii is a widely studied reference organism, particularly in photosynthesis research. It employs photoprotective mechanisms, such as state transitions (ST) and non-photochemical quenching (NPQ), to cope with rapid light changes. Most widely used strains share a recent common ancestor yet differ by up to ~50 000 nuclear variants—genetic diversity that is often overlooked. Even among ‘wild type’ strains, we document significant phenotypic differences, such as pigment accumulation, and nutrient utilization. To elucidate the basis for this variation, we compared transcriptomes and physiological traits of seven commonly used laboratory strains, including the reference strain and the CLiP mutant library parental strain. Despite identical growth conditions, ~40% of genes were differentially expressed between strains. Most of these differences are attributable to changes that have accrued during laboratory propagation, and adverse conditions may have driven transcriptomic drift. At the physiological level, we catalog the range of strain-dependent responses related to photosynthesis and high light (HL) acclimation. Specifically, (i) all strains develop NPQ upon HL exposure, but to various degrees, (ii) they show a substantial variation in ST capacity, and (iii) they regulate the composition of the photosynthetic apparatus differently. We find that NPQ levels do not correlate with LHCSR3 expression, suggesting an additional layer of NPQ regulation. STs are constantly activated and independent of growth light intensities. Overall, our findings highlight significant strain-to-strain differences in virtually all photosynthetic parameters, emphasizing the importance of careful strain selection in future research endeavors.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

Stellar Mergers or Truly Young? Intermediate-age Stars on Highly Radial Orbits in the Milky Way’s Stellar Halo

Reconstructing the mass assembly history of the Milky Way relies on obtaining detailed measurements of the properties of many stars in the galaxy, especially in the stellar halo. One of the most constraining quantities is stellar age, as it can shed light on the accretion time and quenching of star formation in merging satellites. However, obtaining reliable age estimates for large samples of halo stars is difficult. We report published ages of 120 subgiant halo stars with highly radial orbits that likely belong to the debris of the Gaia-Enceladus/Sausage (GES) galaxy. The majority of these halo stars are old, with an age distribution characterized by a median of 11.6 Gyr and a 16th (84th) percentile of 10.5 (12.7) Gyr. However, the distribution is skewed, with a tail of younger stars that span ages down to ~6–9 Gyr. All highly radial halo stars have chemical and kinematic/orbital quantities that associate them with the GES debris. Initial results suggest that these intermediate-age stars are not a product of mass transfer and/or stellar mergers, which can bias their age determination low. If this conclusion is upheld by upcoming spectrophotometric studies, then the presence of these stars will pose an important challenge for constraining the properties of the GES merger and the accretion history of the galaxy.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Modulation of xanthophyll cycle impacts biomass productivity in the marine microalga Nannochloropsis

Life on earth depends on photosynthetic primary producers that exploit sunlight to fix CO 2 into biomass. Approximately half of global primary production is associated with microalgae living in aquatic environments. Microalgae also represent a promising source of biomass to complement crop cultivation, and they could contribute to the development of a more sustainable bioeconomy. Photosynthetic organisms evolved multiple mechanisms involved in the regulation of photosynthesis to respond to highly variable environmental conditions. While essential to avoid photodamage, regulation of photosynthesis results in dissipation of absorbed light energy, generating a complex trade-off between protection from stress and light-use efficiency. This work investigates the impact of the xanthophyll cycle, the light-induced reversible conversion of violaxanthin into zeaxanthin, on the protection from excess light and on biomass productivity in the marine microalgae of the genus Nannochloropsis. Zeaxanthin is shown to have an essential role in protection from excess light, contributing to the induction of nonphotochemical quenching and scavenging of reactive oxygen species. On the contrary, the overexpression of zeaxanthin epoxidase enables a faster reconversion of zeaxanthin to violaxanthin that is shown to be advantageous for biomass productivity in dense cultures in photobioreactors. These results demonstrate that zeaxanthin accumulation is critical to respond to strong illumination, but it may lead to unnecessary energy losses in light-limiting conditions and accelerating its reconversion to violaxanthin provides an advantage for biomass productivity in microalgae.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2025

Too dim, too bright, and just right: Systems analysis of the Chlamydomonas diurnal program under limiting and excess light

Photosynthetic organisms coordinate their metabolism and growth with diurnal light, which can range in intensity from limiting to excessive. Little is known about how light intensity impacts the diurnal program in Chlamydomonas reinhardtii, or how diurnal rhythms in gene expression and metabolism shape photoprotective responses at different times of day. To address these questions, we performed a systems analysis of synchronized Chlamydomonas populations acclimated to low, moderate, and high diurnal light. Transcriptomic and proteomic data revealed that the Chlamydomonas rhythmic gene expression program is resilient to limiting and excess light: genome-wide, waves of transcripts, and proteins peak at the same times in populations acclimated to stressful light intensities as in populations acclimated to moderate light. Yet, diurnal photoacclimation gives rise to hundreds of gene expression changes, even at night. Time course measurements of photosynthetic efficiency and pigments responsive to excess light showed that high light-acclimated cells partially overcome photodamage in the latter half of the day prior to cell division. Although gene expression and photodamage are dynamic over the diurnal cycle, Chlamydomonas populations acclimated to low and high diurnal light maintain altered photosystem abundance, thylakoid architecture, and non-photochemical quenching capacity through the night phase. This suggests that cells remember or anticipate the light intensities that they have typically encountered during the day. The integrated data constitute an excellent resource for understanding photoacclimation in eukaryotes under environmentally relevant conditions.

Dupuis, Sunnyjoy↗
DOE OSTI2020

Transverse momentum broadening of a jet in quark-gluon plasma: an open quantum system EFT

We utilize the technology of open quantum systems in conjunction with the recently developed effective field theory for forward scattering to address the question of massless jet propagation through a weakly-coupled quark-gluon plasma in thermal equilibrium. We discuss various possible hierarchies of scales that may appear in this problem, by comparing thermal scales of the plasma with relevant scales in the effective field theory. Starting from the Lindblad equation, we derive and solve a master equation for the trans- verse momentum distribution of a massless quark jet, at leading orders both in the strong coupling and in the power counting of the effective field theory. Markovian approximation is justified in the weak coupling limit. Using the solution to the master equation, we study the transverse momentum broadening of a jet as a function of the plasma temperature and the time of propagation. We discuss the physical origin of infrared sensitivity that arises in the solution and a way to handle it in the effective field theory formulation. We suspect that the final measurement constraint can only cut-off leading infrared singularities and the solution to the Markovian master equation resums a logarithmic series. This work is a stepping stone towards understanding jet quenching and jet substructure observables on both light and heavy quark jets as probes of the quark-gluon plasma.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Origins of Photoluminescence Instabilities at Halide Perovskite/Organic Hole Transport Layer Interfaces

Metal halide perovskites are promising for optoelectronic device applications; however, their poor stability under solar illumination remains a primary concern. While the intrinsic photostability of isolated neat perovskite samples has been widely discussed, it is important to explore how charge transport layers—employed in most devices—impact photostability. Here, in this paper, we study the effect of organic hole transport layers (HTLs) on light-induced halide segregation and photoluminescence (PL) quenching at perovskite/organic HTL interfaces. By employing a series of organic HTLs, we demonstrate that the HTL’s highest occupied molecular orbital energy dictates behavior; furthermore, we reveal the key role of halogen loss from the perovskite and subsequent permeation into organic HTLs, where it acts as a PL quencher at the interface and introduces additional mass transport pathways to facilitate halide phase separation. In doing so, we both reveal the microscopic mechanism of non-radiative recombination at perovskite/organic HTL interfaces and detail the chemical rationale for closely matching the perovskite/organic HTL energetics to maximize solar cell efficiency and stability.

14 SOLAR ENERGY↗
DOE OSTI2022

Confinement and Collective Escape of Active Particles

Active matter broadly covers the dynamics of self-propelled particles. While the onset of collective behavior in homogenous active systems is relatively well understood, the effect of inhomogeneities such as obstacles and traps lacks overall clarity. Here, we study how interacting, self-propelled particles become trapped and released from a trap. We have found that captured particles aggregate into an orbiting condensate with a crystalline structure. As more particles are added, the trapped condensates escape as a whole. Our results shed light on the effects of confinement and quenched disorder in active matter.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Biomimetic Light Harvesting Complexes Based on Self-Assembled Dye-DNA Nanostructures (Final Technical Report)

A fundamental limitation in the development of artificial molecular light harvesting structures is that generally if one places pigment molecules close enough to achieve very high energy transfer efficiency and absorbance cross section, the dyes interact in such a way that self-quenching occurs. This limits both the optical cross section and the overall efficiency of light capture in such systems. Nature overcomes this problem and achieves efficient energy transfer without self-quenching by controlling the environment, vibration characteristics, orientation and dynamics of the pigments involved in light harvesting. Natural light harvesting systems have evolved highly intricate chromophore architectures of protein-bound organic molecules that absorb and funnel solar energy with high efficiency and fast transfer rates using elegant excitonic circuitries. Nature achieves this precise control over the properties of pigment complexes by using specific proteins as templates to guide the formation of very well-defined pigment aggregates, groups of pigment molecules that are in close enough contact to undergo excitonic interactions resulting in new electronic properties that were not present in the monomer. In synthetic systems, pigment aggregates are well known, and J-aggregates and H-aggregates have been long studied for their unique properties. In Nature, the chlorosomes of green bacteria form what appear to be classical J-aggregates and the light harvesting complexes of purple nonsulfur bacteria form ring structures that have many of the properties of J-aggregates such as a red-shifted absorbance spectrum and excited states that are delocalized over multiple pigment molecules. These photosynthetic systems leverage the spectral and enhanced transport properties of J-like aggregates to achieve fast exciton transport within the antenna and thus high light-harvesting efficiency. The close interaction of the pigments results in substantial electronic coupling that lifts the degeneracy of excitonic states and therefore modifies the absorption and emission spectra of the monomer. In the case of J-aggregation, lower energy excitonic states acquire significant oscillator strength, resulting in a characteristic bathochromic shift of the absorption and fluorescence and often superradiant delocalized exciton states.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2022

The major trimeric antenna complexes serve as a site for qH-energy dissipation in plants

Plants and algae are faced with a conundrum: harvesting sufficient light to drive their metabolic needs while dissipating light in excess to prevent photodamage, a process known as nonphotochemical quenching. A slowly relaxing form of energy dissipation, termed qH, is critical for plants’ survival under abiotic stress; however, qH location in the photosynthetic membrane is unresolved. Here, we tested whether we could isolate subcomplexes from plants in which qH was induced that would remain in an energy-dissipative state. Interestingly, we found that chlorophyll (Chl) fluorescence lifetimes were decreased by qH in isolated major trimeric antenna complexes, indicating that they serve as a site for qH-energy dissipation and providing a natively quenched complex with physiological relevance to natural conditions. Next, we monitored the changes in thylakoid pigment, protein, and lipid contents of antenna with active or inactive qH but did not detect any evident differences. Finally, we investigated whether specific subunits of the major antenna complexes were required for qH but found that qH was insensitive to trimer composition. Because we previously observed that qH can occur in the absence of specific xanthophylls, and no evident changes in pigments, proteins, or lipids were detected, we tentatively propose that the energy-dissipative state reported here may stem from Chl–Chl excitonic interaction.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

A low-cost and realistic noisy light system for studying photosynthesis

Unlike the light conditions commonly used to grow photosynthetic organisms in the research laboratory, the light intensity in real environments is dynamic. A simple and low-cost system is described in which a commercial dimmable LED panel is controlled to simulate a sinusoidal function representing daylight hours and overlaid with stochastic shading events. The output closely resembles light intensity measurements on Earth’s surface on partly cloudy days or in lower levels of plant canopies. Here, this tool may be useful to researchers studying photosynthetic acclimation responses.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2025

Spatiotemporal quenches for efficient critical ground state preparation in the two-dimensional transverse field Ising model

Quantum simulators have the potential to shed light on the study of quantum many-body systems and materials, offering unique insights into various quantum phenomena. Although adiabatic evolution has been conventionally employed for state preparation, it faces challenges when the system evolves too quickly or the coherence time is limited. In such cases, shortcuts to adiabaticity, such as spatiotemporal quenches, provide a promising alternative. This paper numerically investigates the application of spatiotemporal quenches in the two-dimensional transverse field Ising model with ferromagnetic interactions, focusing on the emergence of the ground state and its correlation properties at criticality when the gap vanishes. We demonstrate the effectiveness of these quenches in rapidly preparing ground states in critical systems. Our simulations reveal the existence of an optimal quench front velocity at the emergent speed of light, leading to minimal excitation energy density and correlation lengths of the order of finite system sizes we can simulate. These findings emphasize the potential of spatiotemporal quenches for efficient ground state preparation in quantum systems, with implications for the exploration of strongly correlated phases and programmable quantum computing.

2-dimensional systems↗
DOE OSTI2020

Water-Stable 1D Hybrid Tin(II) Iodide Emits Broad Light with 36% Photoluminescence Quantum Efficiency

The optical and light emission properties of tin and lead halide perovskites are remarkable because of the robust room-temperature (RT) performance, broad wavelength tunability, high efficiency, and good quenching resistance to defects. These highly desirable attributes promise to transform current light-emitting devices, phosphors, and lasers. One disadvantage in most of these materials is the sensitivity to moisture. Here, we report a new air-stable one-dimensional (1D) hybrid lead-free halide material (DAO)Sn 2 I 6 (DAO, 1,8-octyldiammonium) that is resistant to water for more than 15 h. The material exhibits a sharp optical absorption edge at 2.70 eV and a strong broad orange light emission centered at 634 nm, with a full width at half-maximum (fwhm) of 142 nm (0.44 eV). The emission has a long photoluminescence (PL) lifetime of 582 ns, while the intensity is constant over a very broad temperature range (145–415 K) with a photoluminescence quantum yield (PLQY) of at least 20.3% at RT. Above 415 K the material undergoes a structural phase transition from monoclinic (C2/c) to orthorhombic (Ibam) accompanied by a red shift in the band gap and a quench in the photoluminescence emission. Density functional theory calculations support the trend in the optical properties and the 1D electronic nature of the structure, where the calculated carrier effective masses along the inorganic chain are significantly lower than those perpendicular to the chain. As a result, thin films of the compound readily fabricated from solutions exhibit the same optical properties, but with improved PLQY of 36%, for a 60 nm thick film, among the highest reported for lead-free low-dimensional 2D and 1D perovskites and metal halides.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Observation of conformational dynamics in single light-harvesting proteins from cryptophyte algae

Photosynthetic organisms use pigment–protein complexes to capture the sunlight that powers most life on earth. Within these complexes, the position of the embedded pigments is all optimized for light harvesting. At the same time, the protein scaffold undergoes thermal fluctuations that vary the structure, and, thus, photophysics, of the complexes. While these variations are averaged out in ensemble measurements, single-molecule spectroscopy provides the ability to probe these conformational changes. We used single-molecule fluorescence spectroscopy to identify the photophysical substates reflective of distinct conformations and the associated conformational dynamics in phycoerythrin 545 (PE545), a pigment–protein complex from cryptophyte algae. Rapid switching between photophysical states was observed, indicating that ensemble measurements average over a conformational equilibrium. A highly quenched conformation was also identified, and its population increased under high light. This discovery establishes that PE545 has the characteristics to serve as a photoprotective site. Finally, unlike homologous proteins from the evolutionarily related cyanobacteria and red algae, quenching was not observed upon photobleaching, which may allow for robust photophysics without the need for rapid repair or replacement machinery. Collectively, these observations establish the presence of a rich and robust set of conformational states of PE545. Cryptophytes exhibit particularly diverse energetics owing to the variety of microenvironments in which they survive, and the conformational states and dynamics reported here may provide photophysical flexibility that contributes to their remarkable ability to flourish under diverse conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗