Large Absorption Cross Section Research Articles

Mixed-dimensional CsPbBr3@ZnO heterostructures for high-performance p-n diodes and photodetectors

Mixed one-dimensional (1D) and three-dimensional (3D) heterostructures, with synergistic advantages of different dimensionalities, have shown unique optical properties due to their large junction areas and high absorption cross-sections, which may also bring superior electrical and optoelectronic performances. However, due to the challenge in designing and constructing a proper 1D-3D p-n junction, their electronic properties and potential application are still unclear. Here, a type of 1D-3D ZnO/CsPbBr3 p-n junction is constructed by liquid-phase growth of crystalline CsPbBr3 microplates on ZnO nanowires, which exhibit excellent properties of p-n diode and serve as high-performance rectifier and photodetector. As a rectifier, it shows characteristics of ambipolar transfer and its rectification ratio reaches up to 106. As a photodetector, it covers light from ultraviolet to visible light. High photoelectric switching ratio (107), responsivity (3.5 × 103 A/W), detectivity (6.6 × 1013 Jones) and external quantum efficiency (1.7 × 106%) are obtained under 254 nm light illumination. Meanwhile, the switching ratio, responsivity, detectivity and external quantum efficiency are 103, 41.5 A/W, 4.96 × 1012 Jones and 1.086 × 103%, respectively, under 473 nm laser illumination. The decay length of photo-generated carriers in ZnO/CsPbBr3 heterojunction is demonstrated longer than that in original CsPbBr3 crystal, which is further controlled by adjusting the potential barriers between the CsPbBr3 and ZnO with a tunable external electric field.

Concentration Effect of Germanium Dioxide on the Spectroscopic Properties and Laser Performance of Er3+/Yb3+ Co-Doped Phosphate Glasses

The Er3+/Yb3+ co-doped phosphate glasses with GeO2 modification (PGs) were successfully prepared by melt-quenching method. Their physical parameters were investigated such as density, refractive index, glass transition temperature and coefficients of thermal expansion. The phenomenological intensity parameters Ω t (t = 2, 4, 6) of the PGs have been calculated by the Judd-Ofelt theory. The relationship between optical properties and GeO2 concentration was discussed in this work. The laser experiment using PG10 (GeO2 10 mol% modified phosphate glass with Er3+/Yb3+ ratio of 0.5/2) was carried out. The research results indicate that the introduction of GeO2 results in a large absorption and emission cross-section, a long lifetime, a high quantum efficiency, and an excellent laser performance. All these advantages could also portend an optimized method for improving spectroscopic properties in other constituent Er3+/Yb3+ co-doped phosphate glass by introducing GeO2.

Responsive mechanism of 2-fluoro-5-nitrobenzoate based two-photon fluorescent probes for H2Sn detection: A theoretical perspective

Two-photon fluorescent probes with large two-photon absorption (TPA) cross sections have shown wide applications in biomedical domain. However, both the species and amounts of high efficient probes are far from meeting the requirements, one main reason is that the relationship between the molecular structures and the responsive mechanisms are not clear and theoretical framework in this field is not perfect. In this work, the photophysical properties including one- and two-photon absorption and emission of three newly synthesized fluorescent probes for hydrogen polysulfide (H2Sn) detection are investigated by density functional theory and time-dependent density functional theory with the polarizable continuum model in different solvents. Results indicate that the enhanced fluorescent intensity and enlarged TPA cross section can be found when the probes reacted with H2Sn. Moreover, the OPA intensity is largest and its fluorescent intensity is largely enhanced when detecting H2Sn for Pro2, this verifies its superior performance in the detection of H2Sn than Pro1 and Pro 3. Furthermore, the inner mechanism for the increase of TPA cross section is revealed, the responsive mechanisms for photo induced electron transfer (PET) and fluorescence resonance energy transfer (FRET) processes are revealed through analyzing the energies and distributions of frontier orbitals. Our calculations provide theoretical perspectives for experimental measurements and could sever as a useful reference for developing advanced probes in biomedical fields.

Temperature-dependent lattice dynamics in iridium

The characterization of simple elemental systems is key to benchmarking first-principles modeling of electronic and vibrational behaviors of materials. A large body of literature has been built for most elemental systems in the periodic table. However, surprisingly little neutron work has been performed to probe the vibrational properties of iridium, likely due to its large neutron absorption cross section. Nonetheless, iridium is of significant scientific and technological interest due to large relativistic electron effects and electron-phonon coupling, particularly in strongly correlated iridate compounds. Here, we report temperature-dependent inelastic neutron scattering measurements of the vibrational properties of iridium, from which we extract key thermodynamic properties. To overcome the challenge of the large neutron absorption of iridium, we developed a simple postprocessing correction procedure. The measured densities of phonon states compare well with quasiharmonic density functional theory calculations, although the obtained experimental phonon Gr\uneisen parameters are much larger than expected, reaching as high as $\ensuremath{\gamma}=4.5$, indicating substantial anharmonicity.

Millimeter-Deep Detection of Single Shortwave-Infrared-Emitting Polymer Dots through Turbid Media.

Fluorescence imaging at longer wavelengths, especially in the shortwave-infrared (SWIR: 1000-1700 nm) region, leads to a substantial decrease in light attenuation, scattering, and background autofluorescence, thereby enabling enhanced penetration into biological tissues. The limited selection of fluorescent probes is a major bottleneck in SWIR fluorescence imaging. Here, we develop SWIR-emitting nanoparticles composed of donor-acceptor-type conjugated polymers. The bright SWIR fluorescence of the polymer dots (primarily attributable to their large absorption cross-section and high fluorescence saturation intensity (as high as 113 kW·cm-2)) enables the unprecedented detection of single particles as small as 14 nm through millimeter-thick turbid media. Unlike most SWIR-emitting nanomaterials, which have an excited-state lifetime in the range of microseconds to milliseconds, our polymer dots exhibit a subnanosecond excited-state lifetime. These characteristics enable us to demonstrate new time-gated single-particle imaging with a high signal-to-background ratio. These findings expand the range of potential applications of single-particle deep-tissue imaging.

Mechanism of luminescence and efficient energy storage in Lu2SiO5 : Ce3+single crystals

The development of high energy physics and medicine has raised the necessity of heavy stintillating materials with a large total gamma quantum absorption cross-section, high quantum output and fast response. Cerium doped lutetium silicate Lu2SiO5 : Ce3+ (LSO) has high density, large effective atomic number and high conversion efficiency. In this work we have reported optical absorption spectroscopy and photoluminescence data for LSO single crystals grown using the modified Musatov method. The absorption spectra show the fundamental intrinsic absorption edge of Lu2SiO5 at ~200 nm and four extrinsic absorption bands of Ce3+ activator near 250—375 nm. The band gap is 6.19 to 6.29 eV depending on optical beam direction. We have confirmed that the extrinsic absorption bands correspond to optical transitions in Ce3+ activator ions localized in two crystallographically non-equivalent CeI and CeII positions. We have estimated that oscillator force for the optical transitions in Ce3+ ions. The photoluminescence spectra excited by 3.49 eV photon energy UV laser contain three bands: ~2.96 eV, ~3.13 eV (CeI) and ~2.70 eV (CeII). The energy structure of electron traps in LSO has been studied with thermally stimulated luminescence, the crystals being exposed to UV with different spectral and energy parameters. All the experimental thermally stimulated luminescence curves contain at least two peaks at 345 and 400 K with a 4 : 1 intensity ratio attributable to electron traps at 0.92—0.96 and1.12—1.18 eV. LSO exposure to high pressure mercury lamp radiation having the highest energy has for the first time showed the presence of traps at 0.88 eV. A model of the energy structure of LSO has been developed. The luminescence mechanism in the material is more complex than purely intracenter one. We show that high excitation energies may lead to ionization by the mechanism hva + Ce3+ = Ce4+ + e-. We have assumed that the storage of excitation energy involves not only Ce3+ activator but also the conduction band as well as trap states localized near the conduction band.

Fabrication, microstructures, and optical properties of Yb:Lu2O3 laser ceramics from co-precipitated nano-powders

The Yb:Lu2O3 precursor made up of spherical particles was synthesized through the co-precipitation method in the water/ethanol solvent. The 5 at% Yb:Lu2O3 powder is in the cubic phase after calcination at 1100 °C for 4 h. The powder also consists of spherical nanoparticles with the average particle and grain sizes of 96 and 49 nm, respectively. The average grain size of the pre-sintered ceramic sample is 526 nm and that of the sample by hot isostatic pressing grows to 612 nm. The 1.0 mm-thick sample has an in-line transmittance of 81.6% (theoretical value of 82.2%) at 1100 nm. The largest absorption cross-section at 976 nm is 0.96×10−20 cm2 with the emission cross-section at 1033 nm of 0.92×10−20 cm2 and the gain cross sections are calculated with the smallest population inversion parameter β of 0.059. The highest slope efficiency of 68.7% with the optical efficiency of 65.1% is obtained at 1033.3 nm in quasi-continuous wave (QCW) pumping. In the case of continuous wave (CW) pumping, the highest slope efficiency is 61.0% with the optical efficiency of 54.1%. The obtained laser performance indicates that Yb:Lu2O3 ceramics have excellent resistance to thermal load stresses, which shows great potential in high-power solid-state laser applications.

Heterostructures in Two-Dimensional CdSe Nanoplatelets: Synthesis, Optical Properties, and Applications

Semiconductor two-dimensional (2D) nanoplatelets (NPLs) possess narrow emission bandwidths, large absorption cross sections, and low auger recombination rates, which are considered as a promising m...

Donor-Acceptor Conjugated Macrocycles with Polyradical Character and Global Aromaticity.

SummaryPolyradical character and global aromaticity are fundamental concepts that govern the rational design of cyclic conjugated macromolecules for optoelectronic applications. Here, we report donor-acceptor (D−A) conjugated macromolecules with and without π-spacer derivatives to tune the antiferromagnetic couplings between the unpaired electrons. The macromolecules without π-spacer have a closed-shell electronic configuration and show global nonaromatic character in the singlet and lowest triplet states. However, the derivatives with π-spacer develop a nearly pure open-shell diradical and a very high polyradical character, not reported for D−A type macromolecules. Furthermore, the π-spacer derivatives display global nonaromaticity in the singlet ground state, but global aromaticity in the lowest triplet state, according to Baird's rule. The absorption spectra of the open-shell macromolecules calculated with time-dependent density functional theory indicate intensive light absorption in the near-infrared region and broadening to 2,500 nm, making these materials suitable for numerous optoelectronic applications.

Near-field resonant photon sorting applied: dual-band metasurface quantum well infrared photodetectors for gas sensing

Abstract Two photodetectors for measuring transmission and two bulky, separated narrowband filters for picking a target gas absorption line and a non-absorbing reference from broadband emission are typically required for dual-band non-dispersive infrared (NDIR) gas sensing. Metal-dielectric-metal (MDM) metasurface plasmon cavities, precisely controllable narrowband absorbers, suggest a next-generation, nanophotonic approach. Here, we demonstrate a dual-band MDM cavity detector that consolidates the function of two detectors and two filters into a single device by employing resonant photon sorting-a function unique to metasurfaces. Two MDM cavities sandwiching a quantum well infrared photodetector (QWIP) with distinct resonance wavelengths are alternately arranged in a subwavelength period. The large absorption cross section of the cavities ensures ~95% efficient lateral sorting of photons by wavelength into the corresponding detector within a near-field region. The flow of incident photons is thus converted into two independent photocurrents for dual-band detection. Our dual-band photodetectors show competitive external quantum efficiencies up to 38% (responsivity 2.1 A/W, peak wavelength 6.9 5m) at 78 K. By tailoring one resonance to an absorption peak of NO2 (6.25 5m) and the other to a non-absorbing reference wavelength (7.15 5m), NDIR NO2 gas sensing with 10 ppm accuracy and 1 ms response times is demonstrated. Through experiment and numerical simulation, we confirm near-perfect absorption at the resonant cavity and suppressed absorption at its non-resonant counterpart, characteristic of resonant photon sorting. Dual-band sensing across the mid-infrared should be possible by tailoring the cavities and quantum well to desired wavelengths.

Evaluation of shielding efficiency of using boric acid as coolant in CFETR vacuum vessel

Vacuum vessel is a hermetically sealed steel container made up of double steel walls and in-wall shielding, which shields the neutron and protects other components in fusion reactor. Cooling water circulates through the vessel's double steel walls and removes the heat generated during operation. Since boron-10 has a large neutron absorption cross-section, boric acid is supposed to have better shield effect than the original cooling water. In this paper, the effectiveness of pure water and boric acid watery solution as coolant between the double steel walls of the vacuum vessel of CFETR is evaluated by Monte Carlo method. In the simulation, shield efficiency of pure water and different concentration of boric acid is investigated. Neutronic characteristics including neutron flux and neutron spectrum have been calculated. The result shows that boric acid can significantly reduce the flux of total neutron, while the flux of fast neutron takes less change. In conclusion, boric acid has better neutron shielding efficiency than water and can make total neutron flux decline 35%.

Photophysics of Isolated Rose Bengal Anions

Dye molecules based on the xanthene moiety are widely used as fluorescent probes in bioimaging and technological applications due to their large absorption cross-section for visible light and high fluorescence quantum yield. These applications require a clear understanding of the dye's inherent photophysics and the effect of a condensed-phase environment. Here, the gas-phase photophysics of the rose bengal doubly deprotonated dianion [RB - 2H]2-, deprotonated monoanion [RB - H]-, and doubly deprotonated radical anion [RB - 2H]•- is investigated using photodetachment, photoelectron, and dispersed fluorescence action spectroscopies, and tandem ion mobility spectrometry (IMS) coupled with laser excitation. For [RB - 2H]2-, photodetachment action spectroscopy reveals a clear band in the visible (450-580 nm) with vibronic structure. Electron affinity and repulsive Coulomb barrier (RCB) properties of the dianion are characterized using frequency-resolved photoelectron spectroscopy, revealing a decreased RCB compared with that of fluorescein dianions due to electron delocalization over halogen atoms. Monoanions [RB - H]- and [RB - 2H]•- differ in nominal mass by 1 Da but are difficult to study individually using action spectroscopies that isolate target ions using low-resolution mass spectrometry. This work shows that the two monoanions are readily distinguished and probed using the IMS-photo-IMS and photo-IMS-photo-IMS strategies, providing distinct but overlapping photodissociation action spectra in the visible spectral range. Gas-phase fluorescence was not detected from photoexcited [RB - 2H]2- due to rapid electron ejection. However, both [RB - H]- and [RB - 2H]•- show a weak fluorescence signal. The [RB - H]- action spectra show a large Stokes shift of ∼1700 cm-1, while the [RB - 2H]•- action spectra show no appreciable Stokes shift. This difference is explained by considering geometries of the ground and fluorescing states.

Crystal growth, structure, defect, and spectroscopic properties of the Nd3+-doped Y2.8ScAl4.2O12 single crystal

A Nd 3+ -doped Y 2.8 ScAl 4.2 O 12 (Nd:YSAG) single crystal was grown successfully via the Czochralski technology. The crystal structure and crystalline quality of the as-grown Nd:YSAG crystal were determined by the X-ray powder diffraction and X-ray rocking curve, respectively. By X-ray fluorescence analysis, the effective segregation coefficient of Nd 3+ is calculated to be 0.33 in the YSAG crystal. Using the chemical etching method, the dislocation density on the (111)-crystalline face is obtained to be about 3.45 × 10 2 cm −2 . The large absorption cross-section (2.95 × 10 −20 cm 2 ) and wide FWHM (9.8 nm) around 808.8 nm imply a high LD pumping efficiency. The high emission cross-section (3.53 × 10 −20 cm 2 ) at 1336.3 nm and long fluorescence lifetime of Nd 3+ ions (286.20 μs) are beneficial to realize laser output. Thereby, all the results indicate that the Nd:YSAG crystal is a potentially new gain material pumped by a LD for near-infrared laser at 1336.3 nm. • A Nd 3+ :Y 2.8 ScAl 4.2 O 12 crystal was grown successfully by the Czochralski method. • Dislocation density on the (111)-crystalline face is obtained to be 3.45 × 10 2 cm −2 . • A large absorption cross-section (2.95 × 10 −20 cm 2 ) implies high pumping efficiency. • High emission cross-section (3.53 × 10 −20 cm 2 ) is beneficial to realize 1336.3 nm laser. • All results indicate this crystal is a potential gain material for 1336.3 nm laser.

Direct inner-shell photoionization of Xe atoms embedded in helium nanodroplets

We present the first measurements of photoelectron spectra of atomic clusters embedded in superfluid helium (He) nanodroplets. Owing to the large absorption cross section of xenon (Xe) around 100 eV photon energy (4d inner-shell ionization), direct dopant photoionization exceeds charge transfer ionization via the ionized He droplets. Despite the predominant creation of Xe2+ and Xe3+ by subsequent Auger decay of free Xe atoms, for Xe embedded in He droplets only singly charged , k = 1, 2, 3 fragments are observed. Broad Xe+ ion kinetic-energy distributions indicate Coulomb explosion of the ions due to electron transfer to the primary Auger ions from surrounding neutral atoms. The electron spectra correlated with Xe ions emitted from the He nanodroplets contain a low-energy feature and nearly unshifted Xe photolines. These results pave the way to extreme ultraviolet and x-ray photoelectron spectroscopy of clusters and molecular complexes embedded in He nanodroplets.

A potential ultrafast pulse laser crystal with disordered melilite structure: Yb3+: CaLaGa3O7

The Yb3+: CaLaGa3O7 crystal with high-quality was grown successfully by the Czochralski method. The structure parameters of Yb3+: CaLaGa3O7 crystal are determined by the X-ray Rietveld refinement method. The absorption and fluorescence spectra, fluorescence lifetime and laser performance parameters were investigated in detail. The large absorption cross-section (1.14 × 10−20 cm2 for π-polarization and 1.06 × 10−20 cm2 for σ-polarization) of the crystal at around 980 nm indicates that the crystal can be pumped efficiently by the commercialized InGaAs laser diode. The stimulated emission-cross section at 1004 nm was calculated to be 1.11 × 10−20 cm2 for π-polarization and 1.04 × 10−20 cm2 for σ-polarization. The above results reveal that Yb3+: CaLaGa3O7 crystal can be regarded as a potential candidate for realizing tunable solid-state and ultrashort pulsed lasers with LD pumping.

Research of ring RPT method on spherical and cylindrical Double-Heterogeneous systems

Due to the double heterogeneity of the dispersed-particle system, the traditional Volume Homogenization Method (VHM) may have a large calculation deviation. The traditional Reactivity-Equivalent Physical Transformation (RPT) method can be used to deal with the Double-Heterogeneous (DH) system of dispersed fuel particles with relatively small absorption cross section. The deviation is still large for the DH system with dispersed burnable poison particles which has large absorption cross section. The Ring RPT (RRPT) method is an improved RPT method that we have proposed not only to handle the DH system of dispersed fuel particles but also the DH system of dispersed burnable poison particles, and it has been verified in cylindrical DH systems. In this paper the RRPT method is applied to spherical DH systems, and its application range is further analyzed. It is found that the RRPT method has corresponding applicable range when dealing with cylindrical and spherical DH systems. A simple method has been proposed to determine whether a DH system can be processed by the RRPT method, and it provides guidance for the specific application of the RRPT method. And it’s also proved that the RRPT method can treat equivalently the DH systems with the particle types and particle sizes commonly used in engineering. At the same time, through theoretical analysis and calculation verification, and comparison with the calculation results of the Monte Carlo particle model, it is found that the RRPT method is particularly suitable for processing cylindrical DH systems with dispersed-particle burnable poison that the traditional RPT method can’t treat and it is also suitable for spherical DH systems.

2D Cadmium Chalcogenides for Optoelectronics

Two-dimensional(2D) cadmium chalcogenides have triggered worldwide interests due to their unique merits in both structure and physical properties, including thickness-dependent bandgaps, narrow emission line widths, high intrinsic absorption coefficient and large absorption cross sections, etc., rendering their great potential for next-generation electronics and optoelectronics devices. In this article, the progress of 2D cadmium chalcogenides in the past few years is comprehensively reviewed. We first discussed several synthetic strategies for various 2D cadmium chalcogenides. Then, their optoelectronic applications in photodetectors, lasers, LEDs, and piezoelectric devices are summarized and commented in detail. Finally, a brief conclusion of the article and the future prospects of the 2D cadmium chalcogenides are provided.

Sub-single exciton optical gain threshold in colloidal semiconductor quantum wells with gradient alloy shelling

Colloidal semiconductor quantum wells have emerged as a promising material platform for use in solution-processable lasers. However, applications relying on their optical gain suffer from nonradiative Auger decay due to multi-excitonic nature of light amplification in II-VI semiconductor nanocrystals. Here, we show sub-single exciton level of optical gain threshold in specially engineered CdSe/CdS@CdZnS core/crown@gradient-alloyed shell quantum wells. This sub-single exciton ensemble-averaged gain threshold of (Ng)≈ 0.84 (per particle) resulting from impeded Auger recombination, along with a large absorption cross-section of quantum wells, enables us to observe the amplified spontaneous emission starting at an ultralow pump fluence of ~ 800 nJ cm−2, at least three-folds better than previously reported values among all colloidal nanocrystals. Finally, using these gradient shelled quantum wells, we demonstrate a vertical cavity surface-emitting laser operating at a low lasing threshold of 7.5 μJ cm−2. These results represent a significant step towards the realization of solution-processable electrically-driven colloidal lasers.

NIR-IIb excitable bright polymer dots with deep-red emission for in vivo through-skull three-photon fluorescence bioimaging

It is of great significance to study the brain structure and function in deep-tissue for neuroscience research and bio-medical applications because of the urgent demand for precise theranostics. Three-photon fluorescence microscopic (3PFM) bioimaging excited by the light in near-infrared IIb (NIR-IIb, 1,500–1,700 nm) spectral region is one of the most promising imaging techniques with the advantages of high spatial resolution, large imaging depth, and reduced scattering. Herein, a type of NIR-IIb light excitable deep-red emissive semiconducting polymer dots (P-dots) with bright 3PF and large three-photon absorption cross-section (σ3) at 1,550 nm was prepared. Then the P-dots were functionalized with polystyrene polymer polystyrene graft ethylene oxide functionalized with carboxyl groups (PS-PEG-COOH) and modified with NH2-poly(ethylene glycol) (PEG) to synthesis photochemically stable and biocompatible P-dots nanoparticles (NPs). Further the P-dots NPs were utilized for in vivo 3PFM bioimaging of cerebral vasculature with and without the brain skull under 1,550 nm femtosecond (fs) laser excitation. In vivo 3PFM bioimaging of the mice cerebral vasculature at various vertical depths was obtained. Moreover, a vivid three-dimensional structure of the mice vascular architecture beneath the skull was reconstructed. At the depth of 350 µm beneath the brain skull, 3.8 µm blood vessels could still be clearly recognized. NIR-IIb excitable P-dots assisted 3PFM bioimaging has great potential in accurate deep tissue bioimaging.

Multiphoton‐Pumped Highly Polarized Polariton Microlasers from Single Crystals of a Dye‐Coordinated Metal–Organic Framework

AbstractRoom‐temperature, low‐threshold, photostable, cost‐effective, efficient, miniaturized, and all‐solid‐state lasers are highly desirable in many technological and medicinal applications. Here, an archetypical dye laser is introduced, with the above attributes, based on single‐crystalline microplates of a dye‐coordinated metal–organic framework (MOF) without an external cavity, holding a potential to be the next‐generation laser. With an exciton–polariton lasing mechanism combined with large multiphoton absorption cross sections, the lasing thresholds of the three microplates are in the range from 0.34 to 0.12 µJ cm−2 under various optical pumping schemes. The lasing threshold is observed to be reduced with an increment in the order of optical nonlinearity involved in the pumping scheme. Lasing at an extreme‐red region is demonstrated, with a high photostability (with a drop in lasing output as low as 25% after 1.8 × 106 cycles), a large degree of polarization (up to 92%), and an excellent conversion efficiency (up to 12%), thereby realizing a crucial milestone in the field of laser technology.