Weak Emitter Research Articles

Solution-State Studies, X-ray Structure Determination and Luminescence Properties of an Ag(I) Heteroleptic Complex Containing 2,9-Bis(styryl)-1,10-phenanthroline Derivative and Triphenylphosphine

A novel heteroleptic Ag(I) compound, formulated as [AgL(PPh3)]BF4 (1) (where L represents 2,9-bis((E)-4-methoxystyryl)-1,10-phenanthroline and PPh3 stands for triphenylphosphine), was successfully synthesized and thoroughly characterized. The compound’s stability in solution was confirmed through 1D and 2D nuclear magnetic resonance (NMR). The photo-irradiation of the complex in a CDCl3 solution, utilizing a common portable UV lamp emitting at λ = 365 nm, led to the partial transformation of the E,E-geometric isomer to E,Z, ultimately yielding a 1:1.4 molar ratio of isomers. Its molecular structure was determined via X-ray crystallography, while molecular packing was assessed using Hirshfeld calculations. The most notable interactions (51%) within the cationic inner sphere involved H···H bonds. The photophysical characteristics of the complex and L were evaluated both in the solid state and in solution (dichloromethane). Compound 1 is a weak emitter, with photoluminescence quantum yields of 8.6% and 4.3% in solution and the solid state, respectively.

Laminated Flow-Cell Detector with Granulated Scintillator for the Detection of Tritiated Water

Nuclear sites require regular measurements of the air, soil, and groundwater to ensure the safety of the surrounding environment from potentially hazardous levels of contamination. Although high-energy beta and gamma emitters can often be detected instantly using fixed dosimeters, the detection of low-energy beta emitters is a difficult challenge, especially in groundwater, as its radiation is easily self-absorbed by the surrounding medium. Therefore, it is common practice to sample groundwater and transfer it to a laboratory for analysis using Liquid Scintillation Counting. This work demonstrates a new detector design for the real-time monitoring of tritiated water, a weak beta emitter. This design utilizes a flow cell filled with a granulated scintillator to maximize the surface area of the sample. The cavity is made from plastic sheets, which allow rapid manufacture using readily available lamination sheets. A column of SiPMs in coincidence counting mode has been implemented to reduce noise and allow future extensions to the flow cell for greater detection rates while allowing the detector to fit within limited spaces such as groundwater monitoring boreholes. Using multiple concentrations of tritiated water, this detector has been validated and calibrated, obtaining a minimum detection activity of 26.356 ± 0.889 Bq/mL for a 1-day counting period.

Optical Spectroscopy of Classical Be Stars in Old Open Clusters

We performed the optical spectroscopy of 16 classical Be stars in 11 open clusters older than 100 Myr. Ours is the first spectroscopic study of classical Be stars in open clusters older than 100 Myr. We found that the Hα emission strength of most of the stars is less than 40 Å, in agreement with previous studies. Our analysis further suggests that one of the stars, [KW97] 35–12, might be a weak Hα emitter in nature, showing Hα equivalent width of −0.5 Å. Interestingly, we also found that the newly detected classical Be star LS III +47 37b might be a component of the possible visual binary system LS III +47 37, where the other companion is also a classical Be star. Hence, the present study indicates the possible detection of a binary Be system. Moreover, it is observed that all 16 stars exhibit a lesser number of emission lines compared to classical Be stars younger than 100 Myr. Furthermore, the spectral type distribution analysis of B-type and classical Be stars for the selected clusters points out that the existence of CBe stars can depend on the spectral type distribution of B-type stars present in these clusters.

Emergency response implications of tritium in CANDU severe accidents

Tritium is produced in large quantities by heavy-water moderated CANDU reactors. Even though it is only a weak beta emitter, its dose impact during reactor accidents can be important under certain circumstances. Improved models for characterizing the transport of tritium as part of steam and water have been developed as an external model in the MAAP-CANDU severe accident code. Owing to the high mobility of tritiated steam, a large fraction of the radionuclide inventory can be released to the environment, where its contribution to inhalation doses can be significant. Moreover, after the accident, plant evapotranspiration can lead to continued elevated airborne tritium concentrations in contaminated areas, as shown with a simplified environmental transport model. Gamma measurement-based operational intervention levels (OILs) can miss this contribution, and it is proposed to use derived air concentration limits as an additional metric for making decisions about emergency protective actions like evacuation or relocation.

Interaction between light and single quantum-emitter in open Fabry-Perot microcavity

The interaction between light and matter has attracted much attention not only for fundamental research but also for applications. The open Fabry-Perot cavity provides an excellent platform for such a study due to strong optical confinement, spectral and spatial and tunability, and the feasibility of optical fiber integration. In this review, first, the basic properties of open Fabry-Perot cavities and the fabrication techniques are introduced. Then recent progress of weak coupling, strong coupling and bad emitter regimes is discussed. Finally, the challenges to and perspectives in this respect are presented.

A 3D Plasmonic Crossed-Wire Nanostructure for Surface-Enhanced Raman Scattering and Plasmon-Enhanced Fluorescence Detection.

In this manuscript, silver nanowire 3D random crossed-wire woodpile (3D-RCW) nanostructures were designed and prepared. The 3D-RCW provides rich “antenna” and “hot spot” effects that are responsive for surface-enhanced Raman scattering (SERS) effects and plasmon-enhanced fluorescence (PEF). The optimal construction mode for the 3D-RCW, based on the ratio of silver nanowire and control compound R6G, was explored and established for use in PEF and SERS analyses. We found that the RCW nanochip capable of emission and Raman-enhanced detections uses micro levels of analysis volumes. Consequently, and SERS and PEF of pesticides (thiram, carbaryl, paraquat, fipronil) were successfully measured and characterized, and their detection limits were within 5 μM~0.05 µM in 20 µL. We found that the designed 3D plasmon-enhanced platform cannot only collect the SERS of pesticides, but also enhance the fluorescence of a weak emitter (pesticides) by more than 1000-fold via excitation of the surface plasmon resonance, which can be used to extend the range of a fluorescence biosensor. More importantly, solid-state measurement using a 3D-RCW nanoplatform shows promising potential based on its dual applications in creating large SERS and PEF enhancements.

Experimental and Theoretical Studies of a Spirostannole and Formation of a Pentaorganostannate.

A new spirostannole, 1,1′,3,3′-tetrakis(5-methylthiophen-2-yl)-4,4′,5,5′,6,6′,7,7′-octahydro-2,2′-spirobi[benzo[c]stannole] (4), is synthesised and the molecular structure is compared with the optimised geometry from DFT calculations. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) are twice degenerated and show a small HOMO–LUMO energy gap of 3.2 eV. In addition, cyclic voltammetry measurements are conducted and three redox processes are observed. Absorption and emission spectra show maxima at λabs,max 436 nm and λem,max 533 nm, respectively. Spirostannole 4 is a strongly absorbing material, but an extremely weak emitter in solution at 295.15 K. However, when the solution is cooled from 280 to 80 K, the emission becomes visible. The reaction of spirostannole 4 with methyllithium is monitored by NMR spectroscopy at 238.15 K. The 119Sn{1H} NMR signal shifts from −36.0 (4) to −211.0 ppm, which is indicative of the formation of the lithium pentaorganostannate 5. The complex is thermally instable at 295.15 K, but insights into the molecular structure and electronic behaviour are obtained by DFT and TD-DFT calculations.

Quantum Yield Limits for the Detection of Single-Molecule Fluorescence Enhancement by a Gold Nanorod

Fluorescence-based single-molecule optical detection techniques are widely chosen over other methods, owing to the ease of background screening and better signal-to-noise throughput. Nonetheless, the methodology still suffers from limitations imposed by weak emitting properties of most molecules. Plasmonic nanostructures, such as gold nanorods, can significantly enhance the fluorescence signal of a weak emitter, extending the application of these techniques to a wider range of species. In this work, we explore the lower limit of fluorescence quantum yield for single-molecule detection, using a single gold nanorod to enhance molecular fluorescence. We specifically designed an infrared dye with the extremely low quantum yield of 10–4 and a comparatively large Stokes shift of 3000 cm–1 to demonstrate single-molecule detection by fluorescence enhancement. This example allows us to discuss more general cases. We estimate theoretically the optimal excitation wavelength and the plasmon resonance of the rod that maximize the fluorescence signals. We then confirm experimentally the detection of single-molecule fluorescence with an enhancement factor of 3 orders of magnitude for the quantum yield 10–4. Theoretical simulations indicate that single-molecule signals should be detectable for molecules with quantum yield as low as 10–6, provided the dwell time of the molecules in the plasmonic hot spot is long enough.

In situ modulation of gold nanorod's surface charge drives the growth of end-to-end assemblies from dimers to large networks that enhance single-molecule fluorescence by 10 000-fold.

End-to-end assemblies of anisotropic plasmonic nanostructures with small nanogaps are of great interest as they create strong hot spots for enhancing weak fluorescence and/or scattering of molecules. Here we report the growth of dithiol-linked end-to-end assemblies of gold nanorods from dimers to large networks containing thousands of individual nanorods, directed by in situ tuning of nanorod's surface charge. Surface charge was lowered to initiate the aggregation process but was subsequently increased to achieve slow tip-specific growth over seven days to form end-to-end networks of nanorods, which were stable in solution for over one month. Furthermore, we showed that these assemblies contained strong plasmonic hot spots which enhanced the fluorescence signal of a weak emitter by 104-fold. This enhancement is approximately 10-fold larger than that obtained using a single gold nanorod and is comparable to the largest enhancement obtained using more expensive lithographically made in-plane antenna arrays.

Synthesis, characterization and DFT studies of complexes bearing [Re(CO)3]+ core and reactivity towards cyanide ion

Mononuclear rhenium(I) complexes having fac-[Re(CO)3]+ core of general formula fac-[Re(CO)3(L)Cl] have been synthesized in excellent yield by reacting [Re(CO)5Cl] with L1 and L2in a ratio of 1:1 in toluene under inert atmosphere. Here L1 and L2 are N-((quinolin-2-yl)methylene)-9H-fluoren-2-amine and N-((anthracen-10-yl)methylene)quinolin-8-amine respectively. Spectroscopic measurements such as NMR, ESI-MS and IR spectroscopy were used to ensure the formations of desired complexes. Molecular structures of fac-[Re(CO)3(L1)Cl] and fac-[Re(CO)3(L2)Cl] were confirmed by single-crystal X-ray diffraction. The ligands are emissive whereas the metal complexes are weak emitter. A remarkable change in absorption as well as emission behavior was observed in complex 2 upon addition of cyanide ion. Interruption in intraligand charge transfer in complex 2 is the probable reason for the obvious change in spectral response of the same. 1H NMR titration was performed as the evidence of the previously stated fact. The ground and excited-state geometries, absorption properties of rhenium(I) complexes were examined by DFT and TDDFT methods. The natural transition orbital (NTO) and analysis reveal the nature of excitations.

Photophysical Investigation of Silver/Gold Dicyanometallates and Tetramethylammonium Networks: An Experimental and Theoretical Investigation

We report on the structural and luminescence properties of a series of d10 dicyanometallate compounds of formula K3(Me4N)2[M(CN)2]5 (M = Au and Ag). These double salts form isostructural 3D networks in which metallophilic bonding is observed between [M(CN)2]– subunits. Despite their similar structural features, stark differences in luminescence behavior between these crystals are observed. At room temperature Au‐containing crystals are bright emitters at 405 nm while the Ag analog is a weak emitter at 470 nm. At low temperatures the emission of both complexes becomes intense under UV light at a wavelength of 416 nm. Using lifetime measurements, X‐ray crystallography, and Density Functional Theory (DFT) calculations we have been able to assign these emission bands as a transition from a metal‐metal to ligand charge transfer.

In Situ Quantification of [Re(CO)3]+ by Fluorescence Spectroscopy in Simulated Hanford Tank Waste.

A pretreatment protocol is presented that allows for the quantitative conversion and subsequent in situ spectroscopic analysis of [Re(CO)3]+ species in simulated Hanford tank waste. In this test case, the nonradioactive metal rhenium is substituted for technetium (Tc-99), a weak beta emitter, to demonstrate proof of concept for a method to measure a nonpertechnetate form of technetium in Hanford tank waste. The protocol encompasses adding a simulated waste sample containing the nonemissive [Re(CO)3]+ species to a developer solution that enables the rapid, quantitative conversion of the nonemissive species to a luminescent species which can then be detected spectroscopically. The [Re(CO)3]+ species concentration in an alkaline, simulated Hanford tank waste supernatant can be quantified by the standard addition method. In a test case, the [Re(CO)3]+ species was measured to be at a concentration of 38.9 μM, which was a difference of 2.01% from the actual concentration of 39.7 μM.

The emergence of aqueous chemiluminescence: new promising class of phenoxy 1,2-dioxetane luminophores.

The majority of known chemiluminescent compounds produce light through oxidation-dependent mechanisms. The unique notion of triggering chemiluminescence by a chemical reaction other than oxidation was first introduced by Schaap in 1987 with the development of chemically and enzymatically activated phenoxy-dioxetanes. Such dioxetanes are distinctive among chemiluminescent molecules since the oxidized high-energy species, the dioxetane, is stable for years at room temperature. Light emission is selectively activated by deprotection of the phenol-protecting group. The chemiluminescence quantum yields of such dioxetanes are relatively high in organic solvents like DMSO. In aqueous solution, however, light emission efficiency drops by approximately 10 000-fold due to energy loss to water molecules. As we sought to understand the low light emission efficiency in water, we realized that the dioxetane chemiexcitation leads to the release of an excited state benzoate molecule, which is a very weak emitter under aqueous conditions. Thus, we reasoned that emission in aqueous solution could be enhanced, if the emissive nature of the excited benzoate formed in water is improved. Introduction of an electron-withdrawing acrylic group at the ortho position of the phenol donor resulted in an excited benzoate species that emits light with high efficiency in aqueous solutions. A striking 3000-fold increase in chemiluminescence emission was observed by simply using an acrylonitrile substituent on the dioxetane probe. For the first time, scientists now have an effective single-entity chemiluminescent probe that can be used to evaluate biological processes. This discovery promoted us to develop numerous highly efficient chemiluminescent probes for detection of different enzymes and analytes in aqueous solution. We anticipate that further studies in this direction will lead to even better chemiluminescence probes with quantum yield emissions that are even higher than that of the luciferin/luciferase system. In this Feature Article, we describe the insights that led us to develop these unprecedented luminophores and the historical perspective that led to the current generation of chemiluminescent phenoxy-dioxetane probes.

An optimized method using peptide arrays for the identification of in vitro substrates of lysine methyltransferase enzymes

While a number of post-translational modifications (PTM), such as phosphorylation and ubiquitination, have been extensively studied, lysine methylation is emerging as an important PTM with implications in a growing number of diverse cellular processes. To date, there are approximately 5000 identified methylation sites on non-histone proteins, and as the methyllysine proteome expands it becomes important to identify the lysine methyltransferase enzymes responsible for each methylation event. The use of peptide SPOT methylation assay has proven to be a useful in the identification and validation of novel substrates for lysine methyltransferase enzymes as it uses a weak beta emitter coupled with fluorography to detect methylation events. The method described in this paper provides improvements to the typical protocol for this assay, as a highly sensitive tritium assay can be developed with less radioactivity than previously described. This protocol provides an inexpensive alternative to weak beta signal enhancer sprays and washes for use in lysine methylation peptide SPOT arrays, and a simple open-source method for array quantification.

Correlation of Photophysical Properties with the Photoacoustic Emission for a Selection of Established Chromophores

An archetypal study is presented to correlate both the optical and the photoacoustic (PA) properties for a diverse selection of dyes whose structural properties range across organic and inorganic, symmetric and asymmetric, and neutral and cationic systems. Three distinct classes of molecular PA contrast agents have been identified and classified according to their optical-PA response as either (i) linear absorbers linear PA emitter, (ii) saturable absorbers weak PA emitter, or (iii) reverse saturable absorbers nonlinear PA emitter. The molecular characteristics instrumental in determining the nature of the dyes optical absorption properties, i.e., ground state molar extinction coefficient (eg), excited state molar extinction coefficient (ee), and excited state lifetime (τ), are discussed to aid in the interpretation of a molecule’s optical vs PA response. An excellent linear PA emitter is established in crystal violet, which exhibits the strongest possible PA signal under low laser fluence conditions in b...

Strongly enhanced photoluminescence in nanostructured monolayer MoS2 by chemical vapor deposition

Two-dimensional (2D) layered molybdenum disulfide (MoS2) has become a very promising candidate semiconducting material for future optoelectronic devices, owing to its unique properties. However, monolayer MoS2 is still a weak photon emitter, compared with other direct band gap semiconductors, which requires extra techniques or complicated steps to enhance its photon emission efficiency. Here, we demonstrated that nanostructured monolayer MoS2, produced by one-step chemical vapor deposition (CVD) growth, shows highly enhanced PL emission. The effective enhancement factor could be up to ∼43. Our results open the door to manipulating the optical properties of future devices by using nanostructured 2D monolayers.

Mono- to few-layered graphene oxide embedded randomness assisted microcavity amplified spontaneous emission source

The realization of optoelectronic devices using two-dimensional materials such as graphene and its intermediate product graphene oxide (GO) is extremely challenging owing to the zero band gap of the former. Here, a novel amplified spontaneous emission (ASE) system based on a GO-embedded all-dielectric one-dimensional photonic crystal (1DPhC) micro-resonator is presented. The mono- to few-layered GO sheet is inserted within a microcavity formed by two 5-bilayered SiO2/SnO2 Bragg reflectors. Significantly enhanced photoluminescence (PL) emission of GO embedded in 1DPhC is explicated by studying the electric field confined within the micro-resonator using the transfer matrix method. The inherent randomness, due to fabrication limitations, in the on-average periodic 1DPhC is exploited to further enhance the PL of the optically active micro-resonator. The 1DPhC and randomness assisted field confinement reduces the ASE threshold of the mono- to few-layered weak emitter making the realization of an ASE source feasible. Consequently, ASE at the microcavity resonance and at the low-frequency band-edge of photonic stop-band is demonstrated. Variation of the detection angle from 5° to 30°, with respect to the sample surface normal allows reallocation of the defect mode ASE peak over a spectral range of 558–542 nm, making the GO-incorporated 1DPhC a novel and attractive system for integrated optic applications.

Interpretation of the degradation of silicon HIT solar cells due to inadequate front contact TCO work function

The degradation of the open circuit voltage (VOC) and of the I–V characteristics of p+/n amorphous silicon/crystalline silicon heterojunction solar cells (a-Si:H(p+/i)/c-Si(n) HIT cells) due to the use of transparent conducting oxide (TCO) with small work function at the front contact is investigated. The influence of the TCO work function on the band diagrams, carrier profiles and I–V characteristics in the dark and under illumination is studied by means of AFORS-HET device simulations supported by circuit modeling. It is found that when the TCO work function is not high enough to ensure a good ohmic contact with p-type heavily doped a-Si:H(p+) the VOC degradation is due to the rectifying Schottky barrier at the TCO/a-Si:H(p+) interface. On the other hand, if in addition to the small TCO work function the p-type active doping level in a-Si:H(p+) is reduced, the hole concentration in the p+ inversion layer emitter at the hetero-interface significantly drops leading to a strong enhancement of the emitter dark current and to serious VOC degradation. Moreover, if carrier recombination at the hetero-interface is significant, the weak inversion layer emitter may collapse at a relatively low cell voltage leading to total cell failure.

The Sound Field Around a Tuning Fork and the Role of a Resonance Box

Atypical two-tine tuning fork is barely audible when held vibrating at an arm's length. It is enough, however, to touch its base to a table or, better, to a resonance box and the emitted sound becomes much louder. An inquiring student may pose questions: Why is a bare tuning fork such a weak emitter of sound?What is the role of the resonance box?Where does energy connected with larger intensity of emitted acoustic waves come from?

Blending the distinctions among groups of minor bodies: a portrait of the Centaur-comet “transition” object P/2010 C1 (Scotti)

Aims. We present a portrait of the active Centaur P/2010 C1 (Scotti), observed with a well developed comet-like activity (central diffuse coma condensation and an extended sharp tail-like structure) at the heliocentric distance of rh = 5.5 AU. Methods. We analyse multicolour (B, V, R ,a ndI) images taken at the TNG telescope to characterise the dust coma of the active Centaur and to investigate its photometry, colours, and dust production, and to gain hints to its nucleus size. Results. P/2010 C1 (Scotti) has a small nucleus (<4.8 km in radius), with visual colour V − R = 0.49 ± 0.03 typical of the nuclei of Jupiter-family comets, but with a dust coma much redder (B − I = 2.37 ± 0.13) than both the Sun and the typical comet mucleus. It has an integrated R magnitude of mR = 21.41 ± 0.02 and R-Afρ = 34 ± 2 cm (all measured in the reference aperture of radius φ = 2.0 �� ), which is much lower than has been measured for other active Centaurs at similar heliocentric distances. Its dust production rate, Qd = 0.1–15 kg/s, depicts P/2010 C1 (Scotti) as a rather weak dust emitter, with a dust-loss rate comparable to that of the weakest Jupiter-family comets at shorter heliocentric distance and to the weakest active Centaur characterised to now.