Anomalous Emission Research Articles

Anomalous Pressure-Induced Blue-Shifted Emission of Ionic Copper-Iodine Clusters: The Competitive Effect between Cuprophilic Interactions and Through-Space Interactions.

Developing ionic copper-iodine clusters with multiple emitting is crucial for enriching lighting and display materials with various colors. However, the luminescent properties of traditional ionic copper-iodine clusters are often closely associated with low-energy cluster-centered triplet emission, which will redshift further as the Cu⋅⋅⋅Cu bond length decreases. This article utilizes a pressure-treated strategy to achieve an anomalous pressure-induced blue-shifted luminescence phenomenon in ionic Cu4I6(4-dimethylamino-1-ethylpyridinium)2 crystals for the first time, which is based on dominant through-space charge-transfer (TSCT). Herein, we reveal that the more advantageous through-space interactions in the competition between cuprophilic interactions and through-space interactions can lead to a blue-shifted luminescence. High-pressure angle-dispersive X-ray diffraction and high-pressure infrared experiments show that the enhanced through-space interactions mainly originate from forming new intermolecular C-H⋅⋅⋅I hydrogen bonds and the enhancement of van der Waals interactions between organic cations and anionic clusters. Theoretical calculations and experimental studies of excited-state dynamics confirm that the blue-shifted emission is due to the increased energy gap between the excited triplet and ground states caused by the electron delocalization under stronger through-space interactions. This work deepens previous understanding and provides a new avenue to design and synthetic ionic copper-iodine clusters with high-energy TSCT emission.

Multiwavelength identification of millisecond pulsar candidates in the Galactic bulge

Context. The existence of a population of millisecond pulsars in the Galactic bulge is supported, along with other evidence, by the Fermi GeV excess, an anomalous γ-ray emission detected almost 15 years ago in the direction of the Galactic center. However, radio surveys searching for pulsations have not yet revealed bulge millisecond pulsars. Aims. Identifying promising bulge millisecond pulsar candidates is key to motivating pointed radio pulsation searches. Candidates are often selected among steep-spectrum or polarized radio sources, but multiwavelength information can also be exploited: The aim of this work is to pinpoint strong candidates among the yet unidentified X-ray sources. Methods. We investigated the multiwavelength counterparts of sources detected by the Chandra X-ray observatory that have spectral properties expected for millisecond pulsars in the Galactic bulge. We considered that ultraviolet, optical, and strong infrared counterparts indicate that an X-ray source is not a bulge pulsar, while a radio or a faint infrared counterpart makes it a promising candidate. Results. We identify a large population of more than a thousand X-ray sources without optical, ultraviolet, or strong infrared counterparts. Among them, five are seen for the first time in unpublished radio imaging data from the Very Large Array. We provide the list of promising candidates, for most of which follow-up pulsation searches are ongoing.

Observation of anomalous excitonic emission in V-doped WS2 QDs synthesized by hydrothermal method and subsequent mechanical exfoliation

This study focuses on synthesizing vanadium (V) doped 2H phase WS2 via a facile hydrothermal method and subsequent liquid phase mechanical exfoliation of the material into QD-like nanostructures. An increment in dopant percentage from 1 % to 7 % red shifted the band gap of WS2 from 4.15 eV to 3.78 eV. The nanostructures show electronic transition due to B, A, and defect-bound excitons and demonstrate modulation of excitonic behavior with V doping. Low V doping provides the WS2 material with a reduced B/A excitonic peak intensity ratio because of the nonradiative pathways favoring the relaxation of high energy B excitons to A excitons. High V doping results in anomalous emission behavior marked by an increased B/A ratio, attributed to positive trion formation as a result of excess free hole concentration due to the p-type vanadium. The study suggests that V-doped WS2 nanostructures hold potential for technological applications, particularly in spintronics and photonics, emphasizing the importance of engineering exciton dynamics in two-dimensional materials using p-type substitutional dopants.

The Influence of Anomalous Biomass Emissions on ENSO in CESM2

Abstract The influence of biomass burning (BB) aerosols arising from wildfires and agricultural fires on the transient coupled evolution of ENSO is explored in CESM2. For both El Niño and La Niña, two 20-member ensembles are generated from initial states that are predisposed to evolve into ENSO events. For each ENSO phase, one ensemble is forced with the observed BB emissions during satellite-era ENSO events while the other is forced with a climatological annual cycle, with the responses to anomalous BB emissions estimated from inter-ensemble differences. It is found that the regional responses to anomalous BB emissions occur mainly during boreal fall, which is also the time of the climatological seasonal maximum in emissions. Transient responses are identified in precipitation, clouds, and radiation in both the tropics and extratropics. At the onset of El Niño, these include an increase precipitation in the northern branch of the ITCZ and an enhancement of cloud albedo and amount across the Maritime Continent and eastern subtropical Pacific Ocean. Additional responses are identified through the course of El Niño and successive La Niña events, the net effect of which is to strengthen SST anomalies in the eastern Pacific Ocean during El Niño and warm the tropical Pacific Ocean during La Niña. These responses improve simulation of ENSO power, diversity, and asymmetry in CESM2.

Photophysical properties of fisetin embedded in polymer matrix modulated by both bulk polarity and non-bonding interactions

Slow solvation dynamics and abundant non-bonding interactions in polymer matrix can modulate photophysical properties of guest chromophores. In this work, we used fisetin as a fluorescent probe to explore the microenvironment in poly vinyl alcohol (PVA) matrix and its effect on excited-state proton transfer (ESPT). Compared to in PVA solution, fluorescence of fisetin in PVA film is largely enhanced and ESPT barrier is increased. Both bulk polarity of PVA film and site-specific intermolecular hydrogen bonding between water and fisetin were determined to contribute to anomalous absorption and emission properties absent in solutions.

Dibenzoquinone Cyclopentadithiophene Diradicaloids Show Optical Transitions of Different Spin States and Anomalous Near-Infrared Emission.

We have prepared a series of bis(semiquinone) compounds with dithiophene bridges of different length that evolve from closed-shell (smaller compound) to full diradical (longer compound) for which the narrow singlet-triplet energy gap allows the triplet population at 298 K. The medium size system has a variety of photonic properties with absorptions and emission in the optical near-infrared region mediated by a unique case of anti-Kasha emission. A whole set of optical absorption/emission and vibrational steady state spectroscopies as well as picosecond transient absorption spectroscopy, all complemented with spectroelectrochemistry and theoretical calculations, is presented.

Optical, thermal, and structural properties of Er3+ incorporated double perovskite Ca2MgWO6 phosphors

Novel Ca2MgWO6 phosphors doped with xEr3+ (x = 0.5, 1, 2, 3, and 4 mol%) were synthesized using the solid-state reaction method. Using XRD and FTIR analyses, successful product formation was confirmed. Subsequently, the phosphor was optimized by focusing on the characteristic emission peak at 529 nm, arising from the transition 2H11/2 → 4I15/2. The optimal concentration of Er³⁺ for the given host system was determined to be 2 mol%. Meticulous analyses revealed that the optimized phosphor possessed a direct optical band gap of 3.68 eV and the bonding parameter confirmed that the nature of bonding was ionic nature between the dopant and the host. Furthermore, phosphor also demonstrated high thermal stability up to 500 °C, excellent thermal quenching temperature of 357.43 K, and anomalous temperature-dependent emission properties. All these incredible features make the prepared phosphor a promising candidate for multifield applications like light generation, temperature sensing, etc.

Nonadiabatic Molecular Dynamics Simulations Provide Evidence for Coexistence of Planar and Nonplanar Intramolecular Charge Transfer Structures in Fluorazene.

Fluorazene is a model compound for photoinduced intramolecular charge transfer (ICT) between aromatic moieties. Despite intensive studies, both spectroscopic and theoretical, a complete model of its photophysics is still lacking. Especially controversial is the geometry of its ICT structure, or structures. In order to fill in the gaps in the state of knowledge on this important model system, in the present study I report the results of nonadiabatic molecular dynamics (NAMD) simulations of its photorelaxation process in acetonitrile solution. To afford a direct comparison to spectroscopic data, I use the simulation results as the basis for the calculation of the transient absorption (TA) spectrum. The NAMD simulations provide detailed information on the sequence of events during the excited-state relaxation of the title compound. Following initial photoexcitation into the bright S2 state, the molecule undergoes rapid internal conversion into the S1 state, leading to the locally excited (LE) structure. The LE structure, in turn, undergoes isomerization into a population of ICT structures, with geometries ranging from near-planar to markedly nonplanar. The LE → ICT isomerization reaction is accompanied by the decay of the characteristic excited-state absorption band of the LE structure near 2 eV. The anomalous fluorescence emission band of fluorazene is found to originate mainly from the near-planar ICT structures, in part because they dominate the overall population of ICT structures. Thus, the planar ICT (PICT) model appears to be the most appropriate description of the geometry of the ICT structure of fluorazene.

Sensitivity-improved Polarization Maps at 40 GHz with CLASS and WMAP Data

Improved polarization measurements at frequencies below 70 GHz with degree-level angular resolution are crucial for advancing our understanding of the Galactic synchrotron radiation and the potential polarized anomalous microwave emission and ultimately benefiting the detection of primordial B modes. In this study, we present sensitivity-improved 40 GHz polarization maps obtained by combining the CLASS 40 GHz and Wilkinson Microwave Anisotropy Probe (WMAP) Q-band data through a weighted average in the harmonic domain. The decision to include WMAP Q-band data stems from similarities in the bandpasses. Leveraging the accurate large-scale measurements from the WMAP Q band and the high-sensitivity information from the CLASS 40 GHz band at intermediate scales, the noise level at ℓ ∈ [30, 100] is reduced by a factor of 2–3 in the map space. A pixel domain analysis of the polarized synchrotron spectral index (β s ) using the WMAP K band and the combined maps (mean and 16th/84th percentiles across the β s map: −3.08−0.20+0.20 ) reveals a stronger preference for spatial variation (probability to exceed for a uniform β s hypothesis smaller than 0.001) than the results obtained using WMAP K and Ka bands ( −3.08−0.14+0.14 ). The cross-power spectra of the combined maps follow the same trend as other low-frequency data, and validation through simulations indicates negligible bias introduced by the combination method (subpercent level in the power spectra). The products of this work are publicly available on LAMBDA (https://lambda.gsfc.nasa.gov/product/class/class_prod_table.html).

Extreme summer temperature anomalies over Greenland largely result from clear-sky radiation and circulation anomalies

The polar regions have been undergoing amplified warming in recent years. In particular, Greenland has experienced anomalously warm summers with intense melt rates. We employ a surface radiation budget framework to examine the causes for positive and negative summer temperature anomaly events over Greenland from 1979 to 2021. We found a dominant contribution of the clear-sky downwelling longwave radiation and the surface albedo feedback to temperature anomalies. Atmospheric temperature perturbations dominate the effect of anomalous emissivity on clear-sky downwelling longwave radiation. In warm years, enhanced turbulent heat exchange due to increased surface temperature and diabatic warming in the troposphere induces adiabatic heating of the atmosphere, enhanced moisture advection, and a high-pressure anomaly with a blocking-like anti-cyclonic circulation anomaly following peak temperature days. Different modes of natural climate variability, in particular, related to blocking over Greenland, can further amplify or dampen the ongoing warming trend, causing extreme temperature events.

Variable Radio Emission of Neutron Star X-Ray Binary Ser X–1 during Its Persistent Soft State

Ser X–1 is a low-mass neutron star X-ray binary and has been persistently accreting since its discovery in the 1960s. It has always been observed to be in a soft spectral state and has never showed substantial long-term X-ray variability. Ser X–1 has one previous radio observation in the literature in which radio emission was detected during this soft state, which is contrary to the behavior of black hole X-ray binaries. We have recently obtained 10 randomly sampled radio epochs of Ser X–1 in order to further investigate its anomalous soft-state radio emission. Out of 10 epochs, we find 8 nondetections and 2 detections at 10 GHz flux densities of 19.9 ± 4.2 μJy and 32.2 ± 3.6 μJy, respectively. We do not detect polarization in either epoch, ruling out very high polarization levels (≲63% and 34%). We compare these Ser X–1 results to other X-ray binaries and consider explanations for its long-term variable radio behavior.

Growth of CsPbX3 nanocrystals using sol–gel SiO2 solid powders as reactors without capping agents towards anomalous stable emission membranes

To overcome the poor stability of metal halide perovskite nanocrystals (NCs) prepared in organic solvents, a solid reaction method at high temperature was developed using sol–gel porous SiO2 as a reactor. Sol-gel SiO2 powders were used to encapsulate CsPbX3 NCs at high temperatures (600–800 °C) in air to get SiO2/CsPbX3 glass by dispersing growth cites in advance and no ligands added. After NaOH etching, a thin dense SiO2 shell was remained on the surface of CsPbX3 NCs (named as CsPbX3@SiO2).The photoluminescence (PL) quantum yield of the CsPbX3@SiO2 was 86.7 %, in which their PL peak wavelengths were adjusted from 410-707 nm by changing halogen components. The dense SiO2 shell on CsPbX3 NCs blocked the connection of CsPbX3 cores with water and oxygen in the external environment, resulting in CsPbX3@SiO2 revealed extraordinary high stability. After immersing in water for half year, the PL intensity of CsPbX3@SiO2 composites was remained unchanged and the composites still revealed bright PL after heat-treating in boiling water for 14 h. These highly stable composites were used to fabricate a white light-emitting diode, in which the color coordinates are located at (0.36, 0.33), and the color temperature reaches 5169 K which belongs to the warm white light range.

Tunable emission color from lead-free zero-dimensional Mn2+-doped Cs3InCl6 single crystals

In recent years, the magneto-optical properties of zero-dimensional metal halides have attracted widespread interest. In this study, we employed a vacuum solid-state reaction method to synthesize zero-dimensional, lead-free, and all-inorganic Cs3InCl6 single crystals (SCs). In addition to the blue emission of self-trapped excitons (STEs) inherent to pristine Cs3InCl6, the strategic doping with Mn2+ ions not only facilitates multicolor emissions but also significantly boosts the photoluminescence quantum yield (PLQY) from a modest 1.21 % to an impressive 32.18 %. We carried out an exhaustive investigation into the fundamental mechanisms responsible for these multicolor emissions and the intricate compositional transitions that ensue. Furthermore, the pronounced correlation between temperature-dependent photoluminescence (PL) and magnetic characteristics unveiled the genesis of ferromagnetism within both the pristine and Cs3InCl6: xMn2+ samples. The doping-induced modifications in magnetic behavior furnish a coherent explanation for the anomalous inverse temperature dependence emission wavelength shift. Our research highlights the adjustable PL and magnetic attributes of Mn2+ doped Cs3InCl6, yielding invaluable insights that are poised to advance its application in the next wave of optoelectronic and magnetic technologies.

Luminescence Dynamics of BaAl2O4:Eu2+ Phosphor.

We studied steady-state and time-resolved photoluminescence of Eu doped BaAl2O4 phosphor. The undoped BaAl2O4 sample shows a dominant blue emission band at ~ 428nm and two secondary maxima at ~ 405 and 456nm due to F-centre and aggregate defects such as F2 -centre. The samples after doping of Eu at 1-5% show additional emission bands at ~ 485 and 518 nm due to Eu2+ centre and a red emission band at ~ 657nm is attributed to Eu3+ centre. The sample doped with 2% of Eu shows anomalous emission having the dominant peak at ~ 494nm. The average luminescence lifetime of the emission band at ~ 428nm in the undoped sample was estimated to be (3.29 ± 0.91) ns. The average luminescence lifetime of this emission band after doping of Eu was found to increase by 102 orders of magnitude. The intensity of the 428nm blue emission band was found to quench after doping of Eu beyond 3%. The concentration quenching effect was attributed to dipole-quadrupole interaction. Further, a non-radiative fluorescence energy transfer mechanism from an extrinsic Eu2+ centre to an intrinsic F-centre is proposed to describe the luminescence dynamics of the samples.

Atomic-level investigation of structure and formation process of Y3Al5O12 with super-high content of Ce emitting anomalous orange-red emissions

Ce-doped yttrium aluminum garnet (YAG:Ce, Y3Al5O12:Ce) is the most commonly used yellow phosphor in white light-emitting diodes. Recently, we found that (Y1–xCex)3Al5O12:Ce with a super-high content of Ce (x = 0.11–0.21) can be prepared by a polymerized complex method and exhibits anomalous orange–red emission. To understand the nature of this anomalous behavior from the atomic level, we applied high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and scanning transmission electron microscopy–energy dispersive X-ray spectroscopy (STEM-EDS), a state-of-the-art technique that enables analysis of the atomic-level elemental distributions of Al, Y, and Ce. STEM-EDS images on the atomic level were successfully obtained for YAG:Ce. It was found that Ce in Y site has spatially uneven for few nanometers. Ce–K edge extended X-ray absorption fine structure (EXAFS) analysis was also conducted, which revealed a high level of asymmetry around Ce. By combining the STEM-EDS and EXAFS results, a dynamic model for the red emission was proposed. STEM-EDS also revealed that CeO2 nanocrystals were firstly formed with low-temperature annealing and that the reaction of Y with the CeO2 nanocrystals subsequently yielded YAG:Ce, unlike in the conventional one-step high-temperature synthesis.

Anomalous Emission from Li- and Na-like Ions in the Corona Heated via Alfvén Waves

The solar ultraviolet intensities of spectral lines originating from Li- and Na-like ions have been observed to surpass the expectations derived from plasmas with coronal approximation. The violation of the coronal approximation can be partially attributed to nonequilibrium ionization (NEI) due to dynamic processes occurring in the vicinity of the transition region. To investigate the impact of these dynamics in the Alfvén wave-heated coronal loop, a set of equations governing NEI for multiple ion species was solved numerically in conjunction with 1.5-dimensional magnetohydrodynamic equations. Following the injection of Alfvén waves from the photosphere, the system undergoes a time evolution characterized by phases of evaporation, condensation, and quasi-steady states. During the evaporation phase, the ionization fractions of Li- and Na-like ions were observed to increase when compared to the fractions in ionization equilibrium, which led to an enhancement in the intensity of up to 1.6. This over-fractionation of Li- and Na-like ions was found to be induced by the evaporation process. While collisions between shocks and the transition region temporarily led to deviations from ionization equilibrium, on average over time, these deviations were negligible. Conversely, under-fractions of the ionization fraction led to a reduction in intensity down to 0.9 during the condensation phase and the quasi-steady state. Given the dependency of the over/under-fractionation on mass circulations between the chromosphere and the corona, these observations will serve as valuable benchmarks to validate not only Alfvén wave models but also other existing mechanisms on coronal heating.

Detection of Extragalactic Anomalous Microwave Emission in NGC 2903 Using KVN Single-dish Observations

We present the results of the single-dish observations using the Korean VLBI Network to search for anomalous microwave emission (AME) in nearby galaxies. The targets were selected from ‘Mapping the dense molecular gas in the strongest star-forming galaxies' (MALATANG), a legacy survey project of the James Clerk Maxwell Telescope. The MALATANG galaxies are good representatives of local galaxies with enhanced nuclear activity associated with star formation and/or active galactic nuclei (AGNs), providing IR-bright galaxy samples; thus, they are good candidates for AME hosts. Combining with ancillary data, we investigated the radio–IR spectral energy distribution (SED), while searching for AME signals in five galaxies. The AME in NGC 2903 was well detected at a significant confidence level, whereas that in NGC 2146 and M82 was marginal. NGC 1068 and Arp 299 indicated no significant hints, and we provide upper limits for the AME. The best-fit SED exhibited local peaks of the AME components at higher frequencies and with stronger peak fluxes than those in previous studies. This suggested that AME originates from denser environments such as molecular clouds or photodissociation regions rather than warm neutral/ionized medium as commonly suggested by previous studies. Further, our AME-detected targets were observed to exhibit higher specific star formation rates than the other extragalactic AME hosts. Furthermore, AME favored starburst galaxies among our sample rather than AGN hosts. Consequently, this might imply that AGNs are excessively harsh environments for tiny dust to survive.

Modulation of excited state intramolecular proton transfer and intramolecular charge transfer pathways ofsymmetrical azines through micellar medium.

The photophysical studies of fluorescent probes in micellar medium can give a better insight about their interaction with biological membranes. This study attempts to access the photophysical properties of the dual emitting azine based probe diethylamino salicylidene azine dimer (DEASAD) in micellar media. DEASAD showed dual charge transfer emission due to the presence of open enol (480 nm) and closed enol (510 nm) forms in polar protic solvents. Upon increasing the concentration of ionic surfactants, there is a significant increase in the emission intensity of both the enol forms of DEASAD until premicellar concentration. After micellization, occurrence of a new anomalous keto form emission through excited state intramolecular proton transfer (ESIPT) was observed around 530 nm in ionic micelles and its intensity changes depend on the micellar surface charge. The emission studies revealed the position and interaction of DEASAD with the charge of micellar stern layer as confirmed through interaction of metal ion with the probe and control molecules with and without ESIPT and ICT moieties. In contrast, the new anomalous longer wavelength keto form of DEASAD emission was absent in neutral micelles like Triton X-100.

Origin of the Cr3+ concentration-dependent broadband near-infrared emission in Sc2Si2O7.

The challenge of developing phosphors with tailored near-infrared (NIR) emission ranges to meet the diverse demands of various applications is a paramount concern in the contemporary realm of NIR phosphor research. A strong dependence of NIR emission on Cr3+ concentration has been demonstrated in Sc2-xSi2O7:xCr3+, which exhibits an NIR emission band at 840 nm for low Cr3+ doping concentrations (x = 0.001-0.01) and an anomalous NIR emission band at 1300 nm for high Cr3+ doping concentrations (x = 0.01-0.10). Careful investigation of the crystal structure, excitation and emission spectra, and luminescence decay curves indicates that the two NIR emissions can be attributed to the isolated Cr3+ ions and the Cr3+-Cr3+ pairs, respectively. The strong interaction of exchange-coupled Cr3+-Cr3+ pairs is supported by temperature-dependent emission spectra, luminescence decay curves and electron paramagnetic resonance (EPR) measurements. This work provides a new insight into the study of Cr3+-Cr3+ pairs for broadband NIR emission.

Theoretical Analysis of Anomalous Emission of Eu2+ in Crystals By First-Principles Calculation

The 5d-4f transition energies of lanthanides are very versatile, especially the 4f65d1-4f75d0 transition energy of Eu2+ has high luminescence efficiency and is used in various luminescent materials such as phosphors like SrxCa1-xAlSiN3: Eu2+, scintillators, and solid-state lasers, etc. However, there are materials that do not undergo pure 5d-4f transitions, showing the so-called anomalous luminescence instead. The anomalous luminescence is caused by the formation of excitons due to the overlap of the 5d level of Eu2+ with the conduction band and the transition of electrons from the conduction band to the 4f level, resulting in a shift to a lower energy than the general 5d-4f transition energy. A more detailed analysis of this phenomenon is important for the development of novel luminescent materials using Eu2+.In this study, we aimed to theoretically analyze the anomalous luminescence based on first-principles electronic structure calculations. The model clusters of Eu2+-doped crystals consisting of Eu2+ at the substitution site and the surrounding ions were created. Then molecular orbital calculations were performed by the relativistic discrete-variational Xα (DV-Xα) method and subsequently multiplet calculations were performed by the relativistic discrete-variational multi-electron (DVME) method. These first-principles calculations were carried out for Eu2+-doped crystals that show anomalous luminescence and those that do not show anomalous luminescence, and the electronic states of these materials were compared in detail.