Emitter Candidates Research Articles

Rapid Estimation of fwhm for OLED Emission Spectra Using Bond-Length and Bond-Order Alterations.

Color purity is crucial for achieving a high-quality organic light-emitting diode. An essential property for evaluating color purity is the full width at half-maximum (fwhm) of emission spectra. Theoretically estimating fwhm requires the detailed knowledge of vibronic coupling constants for all vibrational modes, which is time-consuming to obtain via quantum mechanical calculations, particularly for optimizing the geometry of the lowest singlet excited state. These calculations pose a bottleneck for high-throughput screening of narrowband emitters. To address this challenge, we propose a simple model to assess the reorganization energy based on the relationship between bond-length alteration (ΔBL) and vertical bond-order alteration (ΔBO) in optimized ground-state structures. Additionally, a one-mode model is employed to rapidly and effectively estimate fwhm. Our new model yields results comparable to experimental data and more accurate theoretical approaches based on vibronic coupling constants of all vibrational modes but with significantly lower computational costs. This model holds promise for the virtual screening of narrowband emitter candidates.

Identifying Lyα emitter candidates with Random Forest: Learning from galaxies in the CANDELS survey

The physical processes that make a galaxy a Lyman alpha emitter have been extensively studied over the past 25 yr. However, the correlations between physical and morphological properties of galaxies and the strength of the Lyα emission line are still highly debated. Here, we investigate the correlations between the rest-frame Lyα equivalent width and stellar mass, star formation rate, dust reddening, metallicity, age, half-light semi-major axis, Sérsic index, and projected axis ratio in a sample of 1578 galaxies in the redshift range of 2 ≤ z ≤ 7.9 from the GOODS-S, UDS, and COSMOS fields. From the large sample of Lyα emitters (LAEs) in the dataset, we find that LAEs are typically common main sequence (MS) star-forming galaxies that show a stellar mass ≤109 M⊙, star formation rate ≤ 100.5 M⊙ yr−1, E(B − V)≤0.2, and half-light semi-major axis ≤1 kpc. Building on these findings, we have developed a new method based on a random forest (RF) machine learning (ML) classifier to select galaxies with the highest probability of being Lyα emitters. When applied to a population in the redshift range z ∈ [2.5, 4.5], our classifier holds a (80 ± 2)% accuracy and (73 ± 4)% precision. At higher redshifts (z ∈ [4.5, 6]), we obtained an accuracy of 73% and precision of 80%. These results highlight the possibility of overcoming the current limitations in assembling large samples of LAEs by making informed predictions that can be used for planning future large-scale spectroscopic surveys.

Secondary electron emission and vacuum electronics

Secondary electron emission serves as the foundation for a broad range of vacuum electronic devices and instrumentation, from particle detectors and multipliers to high-power amplifiers. While secondary yields of at least 3–4 are required in practical applications, the emitter stability can be compromised by surface dynamics during operation. As a result, the range of practical emitter materials is limited. The development of new emitter materials with high yield and robust operation would advance the state-of-the-art and enable new device concepts and applications. In this Perspective article, I first present an analysis of the secondary emission process, with an emphasis on the influence of material properties. From this analysis, ultra-wide bandgap (UWBG) semiconductors and oxides emerge as superior emitter candidates owing to exceptional surface and transport properties that enable a very high yield of low-energy electrons with narrow energy spread. Importantly, exciting advances are being made in the development of promising UWBG semiconductors such as diamond, cubic boron nitride (c-BN), and aluminum nitride (AlN), as well as UWBG oxides with improved conductivity and crystallinity. These advances are enabled by epitaxial growth techniques that provide control over the electronic properties critical to secondary electron emission, while advanced theoretical tools provide guidance to optimize these properties. Presently, H-terminated diamond offers the greatest opportunity because of its thermally stable negative electron affinity (NEA). In fact, an electron amplifier under development exploits the high yield from this NEA surface, while more robust NEA diamond surfaces are demonstrated with potential for high yields in a range of device applications. Although c-BN and AlN are less mature, they provide opportunities to design novel heterostructures that can enhance the yield further.

Design and analysis of a compact micro-ring resonator signal emitter to reduce the uniformity-induced phase distortion and crosstalk in orbital angular momentum (OAM) division multiplexing.

To improve the transmission capacity of an optical system, different multiplexing schemes have been proposed, such as optical time division multiplexing (OTDM), wavelength division multiplexing (WDM), polarization division multiplexing (PolDM), spatial division multiplexing (SDM), etc. One kind of SDM technique to boost the capacity is through modifying the spatial phase structure of an optical beam, which is known as the orbital angular momentum (OAM) division multiplexing. Moreover, the OAM signal emitter can be produced by using mature and high-yield silicon photonic (SiPh) technology, without the need of using bulky optical components or expensive spatial light modulator (SLM). The SiPh-based micro-ring resonator is one of the promising OAM signal emitter candidates, since it is simple, compact and easy to fabricate. However, the device performance is highly subjected to the structural design, and the uniformity-induced phase distortion will significantly degrade the purities of OAM beams; hence, introducing severe OAM signal crosstalk during the OAM division multiplexing. In this work, a compact SiPh-based micro-ring resonator type OAM signal emitter with detailed design parameters is presented and the output signal uniformity issue is comprehensively investigated. Two kinds of the structural optimization are performed by adjusting the angular grating width as well as the grating height. The results indicate that a significant improvement in output OAM beam uniformity can be achieved, with the attenuation factor being improved over 88% at the price of acceptable 4 ∼ 5% coupling efficiency reduction. The variations of the transmission and the uniformity induced by the fabrication error are also analyzed.

Tracing Lyα and LyC Escape in Galaxies with Mg ii Emission

Star-forming galaxies are considered the likeliest source of the H i ionizing Lyman continuum (LyC) photons that reionized the intergalactic medium at high redshifts. However, above z ≳ 6, the neutral intergalactic medium prevents direct observations of LyC. Therefore, recent years have seen the development of indirect indicators for LyC that can be calibrated at lower redshifts and applied in the epoch of reionization. Emission from the Mg ii λλ2796, 2803 doublet has been proposed as a promising LyC proxy. In this paper, we present new Hubble Space Telescope/Cosmic Origins Spectrograph observations for eight LyC emitter candidates, selected to have strong Mg ii emission lines. We securely detect LyC emission in 50% (4/8) of the galaxies with 2σ significance. This high detection rate suggests that strong Mg ii emitters might be more likely to leak LyC than similar galaxies without strong Mg ii. Using photoionization models, we constrain the escape fraction of Mg ii as ∼15%–60%. We confirm that the escape fraction of Mg ii correlates tightly with that of Lyα, which we interpret as an indication that the escape fraction of both species is controlled by resonant scattering in the same low column density gas. Furthermore, we show that the combination of the Mg ii emission and dust attenuation can be used to estimate the escape fraction of LyC statistically. These findings confirm that Mg ii emission can be adopted to estimate the escape fraction of Lyα and LyC in local star-forming galaxies and may serve as a useful indirect indicator at the epoch of reionization.

Carbon trimer as a 2 eV single-photon emitter candidate in hexagonal boron nitride: A first-principles study

Identifying the atomic origin of the well-recognized 2 eV single-photon emitters in hexagonal boron nitride (hBN) has remained a long debate and important for controllable single-photon emission generation. Here, the authors investigate the static and dynamic properties of carbon trimers from first-principles with many-body interactions. Based on the calculated results, they propose C${}_{2}$C${}_{N}$ to be a promising candidate, which has Zero-Phonon Line, Huang-Rhys factor, photoluminescence lifetime and lineshape all in agreement with the current experimental observations. The near-infrared emission from C${}_{2}$C${}_{N}$ is suggested to be another identifier for experimental verification of the nature of single-photon emitters in hBN.

LAGER Lyα Luminosity Function at z ∼ 7: Implications for Reionization

Abstract We present a new measurement of the Lyα luminosity function (LF) at redshift z = 6.9, finding moderate evolution from z = 5.7 that is consistent with a fully or largely ionized z ∼ 7 intergalactic medium. Our result is based on four fields of the LAGER (Lyman Alpha Galaxies in the Epoch of Reionization) project. Our survey volume of 6.1 × 106 Mpc3 is double that of the next largest z ∼ 7 survey. We combine two new LAGER fields (WIDE12 and GAMA15A) with two previously reported LAGER fields (COSMOS and CDFS). In the new fields, we identify N = 95 new z = 6.9 Lyα emitter (LAEs) candidates, characterize our survey’s completeness and reliability, and compute Lyα LFs. The best-fit Schechter LF parameters for all four LAGER fields are in good general agreement. Two fields (COSMOS and WIDE12) show evidence for a bright-end excess above the Schechter function fit. We find that the Lyα luminosity density declines at the same rate as the UV continuum LF from z = 5.7 to 6.9. This is consistent with an intergalactic medium that was fully ionized as early as redshift z ∼ 7 or with a volume-averaged neutral hydrogen fraction of x H I < 0.33 at 1σ.

A [C ii] 158 μm emitter associated with an O i absorber at the end of the reionization epoch

The physical and chemical properties of the circumgalactic medium (CGM) at $z\gtrsim6$ have been studied successfully through the absorption in the spectra of background Quasi-Stellar Objects (QSOs). One of the most crucial questions is to investigate the nature and location of the source galaxies that give rise to these early metal absorbers. Theoretical models suggest that momentum-driven outflows from typical star-forming galaxies can eject metals into the CGM and the intergalactic medium (IGM) at z=5-6. Deep, dedicated surveys have searched for Ly$\alpha$ emission associated with strong CIV absorbers at $z\approx 6$, but only a few Ly$\alpha$ emitter candidates have been detected. Interpreting these detections is moreover ambiguous because Ly$\alpha$ is a resonant line, raising the need for complementary techniques for detecting absorbers' host galaxies. Here, using Atacama Large Millimeter Array (ALMA), we report a [C II] 158$\mu$m emitter associated with a strong low-ionization absorber, OI, at $z=5.978$. The projected impact parameter between OI and [C II] emitter is 20.0 kpc. The measured [C II] luminosity is $7.0\times 10^7$ solar luminosities. Further analysis indicates that strong OI absorbers may reside in the circumgalactic medium of massive halos one to two orders of magnitude more massive than expected values.

SILVERRUSH X: Machine Learning-aided Selection of 9318 LAEs at z = 2.2, 3.3, 4.9, 5.7, 6.6, and 7.0 from the HSC SSP and CHORUS Survey Data

Abstract We present a new catalog of 9318 Lyα emitter (LAE) candidates at z = 2.2, 3.3, 4.9, 5.7, 6.6, and 7.0 that are photometrically selected by the SILVERRUSH program with a machine learning technique from large area (up to 25.0 deg2) imaging data with six narrowband filters taken by the Subaru Strategic Program with Hyper Suprime-Cam and a Subaru intensive program, Cosmic HydrOgen Reionization Unveiled with Subaru. We construct a convolutional neural network that distinguishes between real LAEs and contaminants with a completeness of 94% and a contamination rate of 1%, enabling us to efficiently remove contaminants from the photometrically selected LAE candidates. We confirm that our LAE catalogs include 177 LAEs that have been spectroscopically identified in our SILVERRUSH programs and previous studies, ensuring the validity of our machine learning selection. In addition, we find that the object-matching rates between our LAE catalogs and our previous results are ≃80%–100% at bright NB magnitudes of ≲24 mag. We also confirm that the surface number densities of our LAE candidates are consistent with previous results. Our LAE catalogs will be made public on our project webpage.

Statistical Correlation between the Distribution of Lyα Emitters and Intergalactic Medium H i at z ∼ 2.2 Mapped by the Subaru/Hyper Suprime-Cam

Abstract The correlation between neutral hydrogen (H i) in the intergalactic medium (IGM) and galaxies attracts great interest. We select four fields that include several coherently strong Lyα absorption systems at z ∼ 2.2 detected using background quasars from the whole SDSS/(e) Baryon Oscillation Spectroscopic Survey (BOSS) database. Deep narrowband and g-band imaging are performed using the Hyper Suprime-Cam on the Subaru Telescope. We select 2642 Lyα emitter (LAE) candidates at z = 2.177 ± 0.023 down to the Lyα luminosity of L Lyα ≈ 2 × 1042 erg s−1 to construct the galaxy overdensity maps, covering an effective area of 5.39 deg2. Combining the sample with the Lyα absorption estimated from 64 (e) BOSS quasar spectra, we find a moderate to strong correlation between the LAE overdensity δ LAE and the effective optical depth τ LoS in lines of sight, with P value = 0.09% or <0.01% when the field containing a significant quasar overdensity is included or excluded. Cross-correlation analysis also clearly suggests that up to 4 ± 1 pMpc, LAEs tend to cluster in regions rich in H i gas, as indicated by the high τ LoS, and avoid the low τ LoS regions where the H i gas is deficient. By averaging the τ LoS as a function of the projected distance (d) to LAEs, we find a 30% excess signal at 2σ level at d < 200 pkpc, indicating the dense H i in the circumgalactic medium, and a tentative excess at 400 < d < 600 pkpc in the IGM regime, corroborating the cross-correlation signal detected at about 0.5 pMpc. These statistical analyses suggest that galaxy−IGM H i correlations exist on scales ranging from several hundred pkpc to several pMpc at z ∼ 2.2.

Development of a Fast-Spectrum Self-Powered Neutron Detector for Molten Salt Experiments in the Versatile Test Reactor

The self-powered neutron detector (SPND) is a widely used flux monitor in thermal nuclear reactors. Although this is a mature technology, the current state of the art is tuned for a thermal neutron spectrum, so many of the devices currently in use lack sensitivity to fast neutrons. Because current in SPNDs is produced through nuclear reactions with the neutron flux inside a reactor, sensitivity in SPNDs is determined by the neutron cross section of the neutron-sensitive portion of the detector, termed the emitter. This neutron cross section drops by orders of magnitude between thermal and fast neutron energies for many emitters in currently used SPNDs, with a corresponding drop in current from the detector. This paper discusses efforts to develop a fast-spectrum self-powered neutron detector (FS-SPND) that is sensitive to neutrons with energies ranging from 0.025 eV up to 1 MeV. An in-depth analysis of Evaluated Nuclear Data File (ENDF)/B-VII.1 neutron-capture cross sections was performed, and four new materials were identified that are suitable emitter candidates for use in measuring fast neutrons. All four materials are stable mid-shell nuclei in the region between doubly magic132Sn and208Pb. Each candidate was simulated with the Geant4 Monte Carlo simulation toolkit to optimize overall detector efficiency.

Reconciling escape fractions and observed line emission in Lyman-continuum-leaking galaxies

Context. Finding and elucidating the properties of Lyman-continuum(LyC)-emitting galaxies is an important step in improving our understanding of cosmic reionization. Aims. Although the z ∼ 0.3 − 0.4 LyC emitters found recently show strong optical emission lines, no consistent quantitative photoionization model taking into account the escape of ionizing photons and inhomogenous interstellar medium (ISM) geometry of these galaxies has yet been constructed. Furthermore, it is unclear to what extent these emission lines can be used to distinguish LyC emitters. Methods. To address these questions we construct one- and two-zone photoionization models accounting for the observed LyC escape, which we compare to the observed emission line measurements. The main diagnostics used include lines of [O III], [O II], and [O I] plus sulfur lines ([S II], [S III]) and a nitrogen line ([N II]), which probe regions of different ionization in the ISM. Results. We find that single (one-zone) density-bounded photoionization models cannot reproduce the emission lines of the LyC leakers, as pointed out by earlier studies, because they systematically underpredict the lines of species of low ionization potential, such as [O I] and [S II]. Introducing a two-zone model, with differing ionization parameter and a variable covering fraction and where one of the zones is density-bounded, we show that the observed emission line ratios of the LyC emitters are well reproduced. Furthermore, our model yields LyC escape fractions, which are in fair agreement with the observations and independent measurements. The [O I] λ6300 excess, which is observed in some LyC leakers, can be naturally explained in this model, for example by emission from low-ionization and low-filling-factor gas. LyC emitters with a high escape fraction (fesc ≳ 38%) are deficient both in [O I] λ6300 and in [S II] λλ6716,6731. We also confirm that a [S II] λλ6716,6731 deficiency can be used to select LyC emitter candidates, as suggested earlier. Finally, we find indications for a possible dichotomy in terms of escape mechanisms for LyC photons between galaxies with relatively low (fesc ≲ 10%) and higher escape fractions. Conclusions. We conclude that two-zone photoionization models are sufficient and required to explain the observed emission line properties of z ∼ 0.3 − 0.4 LyC emitters. This is in agreement with UV absorption line studies, which also show the co-existence of regions with high hydrogen column density (i.e., no escape of ionizing photons) and density-bounded or very low column density regions responsible for the observed escape of LyC radiation. These simple but consistent models provide a first step towards the use of optical emission lines and their ratios as quantitative diagnostics of LyC escape from galaxies.

The origin of the escape of Lyman α and ionizing photons in Lyman continuum emitters

Context. Identifying the physical mechanisms driving the escape of Lyman continuum (LyC) photons is crucial for the search of Lyman continuum emitter (LCE) candidates. Aims. To understand the physical properties involved in the leakage of LyC photons, we investigate the connection between the H I covering fraction, H I velocity width, the Lyman α (Lyα) properties, and the escape of LyC photons in a sample of 22 star-forming galaxies, which includes 13 confirmed LCEs. Methods. We fit the stellar continuum, dust attenuation, and absorption lines between 920 Å and 1300 Å to extract the H I covering fractions and dust attenuation. Additionally, we measure the H I velocity widths of the optically thick Lyman series and derive the Lyα equivalent widths (EW), escape fractions (fesc), peak velocities, and fluxes at the minimum of the observed Lyα profiles. Results. Overall, we highlight strong observational correlations between the presence of low H I covering fractions and the observation of (1) low Lyα peak velocities; (2) more flux at the profile minimum; and (3) larger EW(Lyα), fesc(Lyα), and fescobs(LyC). Hence, low column density channels are crucial ISM ingredients for the leakage of Lyα and LyC photons. Additionally, galaxies with narrower H I absorption velocity widths have higher Lyα equivalent widths, larger Lyα escape fractions, and lower Lyα peak velocity separations. This may suggest that these galaxies have low H I column density. Finally, we find that dust also regulates the amount of Lyα and LyC radiation that actually escapes the ISM. Conclusions. The ISM porosity is one of the origins of strong Lyα emission, enabling the escape of ionizing photons in low-z leakers. However, this is not sufficient to explain the largest fescobs(LyC), which indicates that the most extreme LCEs are likely to be density-bounded along all lines of sight to the observer. Overall, the neutral gas porosity provides a constraint for a lower limit to the escape fraction of LyC and Lyα photons, which offers a key estimator for assessing the leakage of ionizing photons.

New Insights on Lyα and Lyman Continuum Radiative Transfer in the Greenest Peas*

Abstract As some of the only Lyman continuum (LyC) emitters at z ∼ 0, Green Pea (GP) galaxies are possible analogs of the sources that reionized the universe. We present HST COS spectra of 13 of the most highly ionized GPs, with [O iii]/[O ii] = 6–35, and investigate correlations between Lyα, galaxy properties, and low-ionization UV lines. Galaxies with high [O iii]/[O ii] have higher Hα equivalent widths (EWs), and high intrinsic Lyα production may explain the prevalence of high Lyα EWs among GPs. While the Lyα escape fraction is closely linked to low gas covering fractions, implying a clumpy gas geometry, narrow Lyα velocity peak separation ( ) correlates with the ionization state, suggesting a density-bounded geometry. We therefore suggest that may trace the residual transparency of low-column-density pathways. Metallicity is associated with both [O iii]/[O ii] and . This trend may result from catastrophic cooling around low-metallicity star clusters, which generates a compact geometry of dense clouds within a low-density inter-clump medium. We find that the relative strength of low-ionization UV emission to absorption correlates with Lyα emission strength and is related to Lyα profile shape. However, as expected for optically thin objects, the GPs with the lowest show both weak low-ionization emission and weak absorption. The strengths of the low-ionization absorption and emission lines in a stacked spectrum do not correspond to any individual spectrum. Galaxies with high [O iii]/[O ii] contain a high fraction of LyC emitter candidates, but [O iii]/[O ii] alone is an insufficient diagnostic of LyC escape.

MOS spectroscopy of protocluster candidate galaxies at z = 6.5

ABSTRACT The epoch corresponding to a redshift of z ∼ 6.5 is close to full re-ionization of the Universe, and early enough to provide an intriguing environment to observe the early stage of large-scale structure formation. It is also an epoch that can be used to verify the abundance of a large population of low luminosity star-forming galaxies that are deemed responsible for cosmic re-ionization. Here, we present the results of follow-up multi-object spectroscopy using OSIRIS at Gran Telescopio Canarias of 16 Ly α emitter (LAE) candidates discovered in the Subaru/XMM Newton Deep Survey. We have securely confirmed 10 LAEs with sufficient signal-to-noise ratio of the Ly α emission line. The inferred star formation rates of the confirmed LAEs are on the low side, within the range 0.9–4.7 M⊙ yr−1. However, they show relatively high Ly α rest frame equivalent widths. Finally we have shown that the mechanical energy released by the star formation episodes in these galaxies is enough to create holes in the neutral hydrogen medium such that Lyman continuum photons can escape to the intergalactic medium, thus contributing to the re-ionization of the Universe.

Subaru narrow-band imaging search for Lyman continuum from galaxies at z > 3 in the GOODS-N field

Abstract We report results of a search for galaxies at z > 3 with Lyman continuum (LyC) emission using a narrow-band filter NB359 with Subaru/Suprime-Cam in an ∼800 arcmin2 blank field around the GOODS-N. We use 103 star-forming galaxies (SFGs) and 8 active galactic nuclei (AGNs) with spectroscopic redshifts in a range between 3.06 and 3.5 and 157 photometrically selected z = 3.1 Lyman α emitter (LAE) candidates as the targets. After removing galaxies spectroscopically confirmed to be contaminated by foreground sources, we found two SFGs and one AGN as candidate LyC-emitting sources among the targets with spectroscopic redshifts. Among LAE candidates, five sources are detected in the NB359 image, and three among them may be contaminated by foreground sources. We compare the sample galaxies in the GOODS-N with those in the SSA22, where a prominent protocluster at z = 3.1 is known and an LyC search using the same NB359 filter has been made. The frequency of galaxies with LyC leakage in the SSA22 field may be about two times higher than that of galaxies in the GOODS-N with the sample ultraviolet (UV) magnitude range, although the numbers of LyC detections in these fields are too small to make a statistically significant conclusion. By combining the sample galaxies in these fields, we place the 3σ upper limits of the observed LyC-to-UV flux density ratio and LyC escape fraction for galaxies at z = 3.1 with absolute UV magnitude MUV < −18.8 as (fLyC/fUV)obs < 0.036 and $f_\mathrm{esc}^\mathrm{abs}\,\lt\, 8$ per cent, respectively.

Inorganic and Hybrid Perovskite Based Laser Devices: A Review.

Inorganic and organic-inorganic (hybrid) perovskite semiconductor materials have attracted worldwide scientific attention and research effort as the new wonder semiconductor material in optoelectronics. Their excellent physical and electronic properties have been exploited to boost the solar cells efficiency beyond 23% and captivate their potential as competitors to the dominant silicon solar cells technology. However, the fundamental principles in Physics, dictate that an excellent direct band gap material for photovoltaic applications must be also an excellent light emitter candidate. This has been realized for the case of perovskite-based light emitting diodes (LEDs) but much less for the case of the respective laser devices. Here, the strides, exclusively in lasing, made since 2014 are presented for the first time. The solution processability, low temperature crystallization, formation of nearly defect free, nanostructures, the long range ambipolar transport, the direct energy band gap, the high spectral emission tunability over the entire visible spectrum and the almost 100% external luminescence efficiency show perovskite semiconductors’ potential to transform the nanophotonics sector. The operational principles, the various adopted material and laser configurations along the future challenges are reviewed and presented in this paper.

Properties and redshift evolution of star-forming galaxies with high [O III]/[O II] ratios with MUSE at 0.28 < z < 0.85

We present a study of the [O III]/[O II] ratios of star-forming galaxies drawn from Multi-Unit Spectroscopic Explorer (MUSE) data spanning a redshift range 0.28 < z < 0.85. Recently discovered Lyman continuum (LyC) emitters have extremely high oxygen line ratios: [O III]λ5007/[O II]λλ3726, 3729 > 4. Here we aim to understand the properties and the occurrences of galaxies with such high line ratios. Combining data from several MUSE Guaranteed Time Observing (GTO) programmes, we select a population of star-forming galaxies with bright emission lines, from which we draw 406 galaxies for our analysis based on their position in the z-dependent star formation rate (SFR)–stellar mass (M∗) plane. Out of this sample 15 are identified as extreme oxygen emitters based on their [O III]/[O II] ratios (3.7%) and 104 galaxies have [O III]/[O II] > 1 (26%). Our analysis shows no significant correlation between M∗, SFR, and the distance from the SFR−M∗ relation with [O III]/[O II]. We find a decrease in the fraction of galaxies with [O III]/[O II] > 1 with increasing M∗, however, this is most likely a result of the relationship between [O III]/[O II] and metallicity, rather than between [O III]/[O II] and M∗. We draw a comparison sample of local analogues with ⟨z⟩ ≈ 0.03 from the Sloan Digital Sky Survey, and find similar incidence rates for this sample. In order to investigate the evolution in the fraction of high [O III]/[O II] emitters with redshift, we bin the sample into three redshift subsamples of equal number, but find no evidence for a dependence on redshift. Furthermore, we compare the observed line ratios with those predicted by nebular models with no LyC escape and find that most of the extreme oxygen emitters can be reproduced by low metallicity models. The remaining galaxies are likely LyC emitter candidates.

Excitonic gain and laser emission from mixed-cation halide perovskite thin films

Organic–inorganic halide perovskites have recently developed into a potential semiconductor coherent light emitter candidate beyond their promise in solar cell applications. However, despite the ample demonstrations of perovskite lasers, experimental results on the origin of optical gain in perovskites are still elusive. Here, we analyze the excitonic gain in the green from mixed-cation halide perovskites Cs0.17[CH(NH2)2]0.83PbBr3 (Cs0.17FA0.83PbBr3) by both low temperature absorption/emission spectroscopies and ultrafast pump–probe transient absorption experiments. The perovskite thin films show a robust excitonic feature up to room temperature, with estimated exciton binding energy E b =43.8 meV, which can be maintained under high electronic excitations that are required for lasers. By using a high-quality (Q=1350) vertical cavity consisting of sputtered dielectric HfO2/SiO2 distributed Bragg reflectors with perovskite optical gain medium embedded inside, we have demonstrated excitonic-gain-enabled optically pumped lasing, with improved threshold of 13.5±1.4 μJ/cm2 and device longevity lifetime >35 h (108 laser shots) at ambient environment under sustained pulsed optical excitations (3.493 eV, τpulse=0.34 ns, 1 kHz). Understanding and exploiting excitonic gain from perovskite thin film materials may help to further boost the performance of perovskite-based lasers.

Novel electrochemiluminescent platform based on gold nanoparticles functionalized Ti doped BiOBr for ultrasensitive immunosensing of NT-proBNP

Heart failure is a serious medical condition and has become one of the world’s biggest killers. N-terminal pro-B-type natriuretic peptide (NT-proBNP) has been recommended as a new biomarker of excellent prognosis-predictive ability for heart failure. Herein, a label-free electrochemiluminescence (ECL) immunosensor based on gold nanopariticles (Au NPs) functionalized Ti doped BiOBr (Ti:BiOBr-Au) is fabricated for the detection of NT-proBNP. Firstly, three-dimensional flower-like Ti doped BiOBr (Ti:BiOBr), which is firstly proposed with ECL property, is employed as both the ECL substrate and emitter to simplify the construction procedure. In the presence of K2S2O8, the formed Ti:BiOBr can generate stronger ECL signal than pure BiOBr. Due to the large specific surface area, Ti:BiOBr is functionalized with large amounts of Au NPs to further improve ECL emission. Under optimal experimental conditions, a linear response range for NT-proBNP detection from 0.001 ng mL−1 to 50 ng mL−1 is obtained with a detection limit of 0.33 pg mL−1. Featuring high sensitivity and excellent reproducibility, the proposed ECL immunosensor blazes a novel trail for the sensitive determination of NT-proBNP and other biomarkers. It is worth noting that Ti:BiOBr with stable ECL emission displays tremendous potential in ECL bioanalysis as a novel type of emitter candidates.