Quantum Efficiency Research Articles

Study on structural luminescence characteristics of a new Dy3+ activated white luminescent phosphor

A series of Y1-xGa1.5Al1.5(BO3)4: xDy3+ were prepared by a high-temperature solid-phase method. Rietveld refinement characterized the phase purity of the samples obtained, suggesting that the prepared phosphors were high-purity material phases. After synthesizing high purity phase, the luminescence mechanism is revealed, under 348 nm excitation in Y0.97Ga1.5Al1.5(BO3)4: 0.03Dy3+ phosphor, the samples have two characteristic peaks at 480 nm and 572 nm and the burst mechanism is dipole-dipole mechanism. The mechanism of luminescence and quenching is analyzed by analyzing the band structure, and the relationship between the band gap and thermal stability is explained. The prepared phosphor has a quantum efficiency of 51.22 % and exhibits intense white light emission. The thermal stability of the samples was characterized, and the phosphor could still achieve 88.20 % thermal stability at 423 K. Finally, the chromaticity coordinates of the Y1-xGa1.5Al1.5(BO3)4: xDy3+ phosphors all fall in the white-light region, with the color coordinates around (0.33, 0.33). By combining with the 365 nm chip and Y0.97Ga1.5Al1.5(BO3)4: 0.03Dy3+ phosphor, the W-led device with Ra = 68.3 and CCT = 6670 K was synthesized. Therefore, the Y0.97Ga1.5Al1.5(BO3)4: 0.03Dy3+ phosphor prepared in this experiment has some application value in the field of solid-state lighting.

Impact of solvation on the photoisomerisation dynamics of a photon-only rotary molecular motor

The optimization of the quantum efficiency of single-molecule light-driven rotary motors typically relies on chemical modifications. While, in isolated conditions, computational methods have been frequently used to design more efficient motors, the role played by the solvent environment has not been satisfactorily investigated. In this study, we used multiscale nonadiabatic molecular dynamics simulations of the working cycle of a 2-stroke photon-only molecular rotary motor. The results, which display dynamics consistent with the available transient spectroscopy measurements, predict a considerable decrease in the isomerisation quantum efficiency in methanol solution with respect to the gas phase. The origin of such a decrease is traced back to the ability of the motor to establish hydrogen bonds with solvent molecules. The analysis suggests that a modified motor with a reduced ability to form hydrogen bonds will display increased quantum efficiency, therefore extending the set of engineering rules available for designing light-driven rotary motors.

Monoammonium Modified Dion-Jacobson Quasi-2D Perovskite for High Efficiency Pure-Blue Light Emitting Diodes.

Quasi-2D perovskites exhibit impressive optoelectronic properties and hold significant promise for future light-emitting devices. However, the efficiency of perovskite light-emitting diodes (PeLEDs) is seriously limited by defect-induced nonradiative recombination and imbalanced charge injection. Here, the defect states are passivated and charge injection balance is effectively improved by introducing the additive cyclohexanemethylammonium (CHMA) to bromide-based Dion-Jacobson (D-J) structure quasi-2D perovskite emission layer. CHMA participates in the crystallization of perovskite, leading to high quality film composed of compact and well-contacted grains with enhanced hole transportation and less defects. As a result, the corresponding PeLEDs exhibit stable pure blue emission at 466nm with a maximum external quantum efficiency (EQE) of 9.22%. According to current knowledge, this represents the highest EQE reported for pure-blue PeLEDs based on quasi-2D bromide perovskite thin films. These findings underscore the potential of quasi-2D perovskites for advanced light-emitting devices and pave the way for further advancements in PeLEDs.

An efficient “hot exciton” fluorophore based on a dicyanophenanthrene-triphenylamine hybrid

The study presents the design, synthesis, and characterization of DCNP-2TPA, a novel “hot exciton” fluorophore featuring a donor-acceptor structure combining dicyanophenanthrene and triphenylamine. Through a comprehensive analysis including structural examination, theoretical modeling, and optical assessments, the suitability of DCNP-2TPA for integration into organic light-emitting diodes (OLEDs) is evaluated. Comparative to existing dicyanophenanthrene-based emitters, DCNP-2TPA demonstrates significantly enhanced luminescence efficiency, by virtue of the incorporation of two triphenylamine moieties with moderate electron-donating strength. Furthermore, DCNP-2TPA exhibits aggregation-induced emission (AIE) properties and showcases hybridized local and charge-transfer (HLCT) excited states, offering an efficient "hot exciton" channel for triplet harvesting. Employing DCNP-2TPA as the emissive core, OLED devices achieve a noteworthy external quantum efficiency of 8.42 %, highlighting the promise of DCNP-2TPA as an efficient candidate for OLED applications.

Improved Charge Injection Balance in Quantum Dot Light-Emitting Diodes through Interface Texture.

The existing methods to improve the charge balance of quantum dot light-emitting diodes (QLEDs) rely on energy-level matching, but these approaches have been limited by material availability and Fermi-level pinning. Here, we propose a solution that does not require changes to the materials' electronic properties. By using nanoimprinting technology to texture the interface between the hole-transporting layer (HTL) and colloidal quantum dot (CQD) layer, we can increase the HTL-CQD contact area. This significantly enhances the hole injection rate while keeping the electron injection rate essentially unchanged. Compared with the conventional planar structure, QLEDs with textured HTL exhibit lower luminance threshold voltage, significantly higher external quantum efficiency at low bias voltages, improved operational stability, and a similar Lambertian factor. Comprehensive measurements confirm that the HTL-CQD interface texture allows more efficient hole injection into CQDs to occur under lower bias, resulting in less CQD charging and more efficient exciton recombination.

Raman amplifier based on stimulated Raman scattering in a methane-filled hollow core fiber

This article reports on a single pass amplifier based on stimulated Raman scattering in a methane-filled negative curvature hollow core fiber (HCF) to transition 1.06 μm power to 1.54 μm. The researchers measured the highest average Raman power at a single frequency in a methane filled HCF to date of 4.92 W (246 μJ/pulse), with a high average quantum efficiency of 95.9%. A numerical model for the system was developed and shows good agreement with measured thresholds and efficiencies. Model results from a trade space study indicate configuration regimes necessary to maximize 1.54 μm power while avoiding power loss from the secondary shift.

CuGaS2@NH2-MIL-125(Ti) nanocomposite: Unveiling a promising catalyst for photocatalytic hydrogen generation

The development of efficient nanocomposites represents a promising strategy for enhancing the transfer and separation of photogenerated carriers within metal-organic frameworks (MOFs) for photocatalytic H2 generation. In this study, we report, for the first time, the successful fabrication of a novel CuGaS2@NH2-MIL-125(Ti) nanocomposite in a two-step synthesis, consisting of octahedral NH2-MIL-125(Ti) metal-organic frameworks interspersed with flat hexagonal plates of CuGaS2. The CuGaS2@NH2-MIL-125(Ti) nanocomposite effectively mitigates the recombination rate of photogenerated electron-hole pairs. Notably, the most active CuGaS2@NH2-MIL-125(Ti) composite (containing 30 wt% CuGaS2) achieves a remarkable hydrogen generation rate of 965.07 μmol/gcat, surpassing the performance of NH2-MIL-125(Ti) and CuGaS2 by approximately 83 and 144 times, respectively. Additionally, the apparent quantum efficiency for the most active material at a wavelength of 380 nm is 9.07%. This study provides valuable insights into the design of efficient I-III-VI2 compound-MOF nanocomposites for H2 generation applications.

Ultrathin, High-Aspect-Ratio Bismuth Sulfohalide Nanowire Bundles for Solution-Processed Flexible Photodetectors.

In this study, a novel synthesis of ultrathin, highly uniform colloidal bismuth sulfohalide (BiSX where X = Cl, Br, I) nanowires (NWs) and NW bundles (NBs) for room-temperature and solution-processed flexible photodetectors are presented. High-aspect-ratio bismuth sulfobromide (BiSBr) NWs are synthesized via a heat-up method using bismuth bromide and elemental S as precursors and 1-dodecanethiol as a solvent. Bundling of the BiSBr NWs occurs upon the addition of 1-octadecene as a co-solvent. The morphologies of the BiSBr NBs are easily tailored from sheaf-like structures to spherulite nanostructures by changing the solvent ratio. The optical bandgaps are modulated from 1.91 (BiSCl) and 1.88eV (BiSBr) to 1.53eV (BiSI) by changing the halide compositions. The optical bandgap of the ultrathin BiSBr NWs and NBs exhibits blueshift, whose origin is investigated through density functional theory-based first-principles calculations. Visible-light photodetectors are fabricated using BiSBr NWs and NBs via solution-based deposition followed by solid-state ligand exchanges. High photo-responsivities and external quantum efficiencies (EQE) are obtained for BiSBr NW and NB films even under strain, which offer a unique opportunity for the application of the novel BiSX NWs and NBs in flexible and environmentally friendly optoelectronic devices.

Highly Efficient Hybrid White Organic Light‐Emitting Diodes with External Quantum Efficiency Exceeding 30% by Integrating Electron‐Trapping Sensitized Structure and Gradient‐Doping System

AbstractIn this work, efficient two‐color (blue and yellow) hybrid white organic light‐emitting diodes (WOLEDs) with high efficiencies are constructed by introducing iridium(III) bis(4,6‐(difluorophenyl) pyridinato‐N,C2’)picolinate (FIrpic) as electron sensitizer. Experimental results demonstrate that FIrpic with the deep lowest unoccupied molecular orbital (LUMO) level enables preferential electron trapping to collect excessive electrons, thus realizing carrier's balance and high recombination probability. The obtained cool WOLED exhibits the maximum external quantum efficiency (EQE), current efficiency (ηc), and power efficiency (ηp) of 31.05%, 76.36 cd A−1 and 69.92 lm W−1, respectively. Moreover, by gradient doping FIrpic into yellow EML, the generated forward built‐in electric field originating from gradient electrons distribution reduces carriers transport resistance and improves the transport of holes; the diffusion effect of gradient electrons distribution promotes electrons’ transport, thus enhancing the utilization probabilities of carriers and excitons. Besides, FIrpic acts also as an energy transfer ladder to facilitate the energy transfer from host to yellow emitter. Consequently, warm WOLED with enhanced yellow emission achieves the maximum EQE, ηc, and ηp of 33.27%, 75.66 cd A−1 and 88.04 lm W−1, respectively.

Linearly Arranged Multi-π-Stacked Structure for Efficient Through-Space Charge-Transfer Emitters.

Noncovalent spatial interaction has become an intriguing and important tool for constructing optoelectronic molecules. In this study, we linearly attached three conjugated units in a multi π-stacked manner by using just one trident bridge based on indeno[2,1-b]fluorene. To achieve this structure, we improved the synthetic approach through double C-H activation, significantly simplifying the preparation process. Due to the proximity of the C10, C11, and C12 sites in indeno[2,1-b]fluorene, we derived two novel donor|acceptor|donor (D|A|D) type molecules, 2DMB and 2DMFB, which exhibited closely packed intramolecular stacking, enabling efficient through-space charge transfer. This molecular construction is particularly suitable for developing high-performance thermally activated delayed fluorescence materials. With donor(s) and acceptor(s) constrained and separated within this spatially rigid structure, elevated radiative transition rates, and high photoluminescence quantum yields were achieved. Organic light-emitting diodes incorporating 2DMB and 2DMFB demonstrated superior efficiency, achieving maximum external quantum efficiencies of 28.6% and 16.2%, respectively.

Thermally stable luminescence and dosimetric features of Ho(III) activated tungstate double perovskite

Luminescent efficient tungstate double perovskites Ca3WO6 doped with Ho3+ were synthesized via the solid-state reaction at 1200 C°. The resulting phosphors were analyzed using Rietveld refinement of X-ray diffraction (XRD) data, confirming a monoclinic crystal structure with crystallite sizes ranging between 50 and 55 nm. Optical bandgap determination was facilitated by diffusion reflectance spectra (DRS). Fourier transform infrared (FTIR) studies were conducted to identify functional group vibrations. The optical excitation of the Ca3WO6:Ho3+ phosphors under different excitation conditions resulted in intense green photoluminescence (PL) emission at 545 nm, indicative of the 5F4–5I8 transition of Ho3+ ions. Thermal stability assessment of Ca3WO6:1 % Ho3+ phosphor under blue excitation (454 nm) revealed good thermally stable luminescence about 85.32 % at LED working temperature (150 °C). PL decay studies were conducted to analyze fluorescent behaviour, wherein by means of PL decay lifetime, the PL quantum efficiency of Ca3WO6:1 % Ho3+ phosphor is computed to be 91.1 %. The CIE color coordinates of the phosphors being investigated reside within the green spectral region, with a calculated color purity of 93.25 % observed for Ca3WO6:1%Ho3+. Furthermore, the phosphors under study exhibited high-quality thermoluminescence (TL) after beta irradiation. The detailed TL characterization conducted to assess dosimetric properties. The impact of Ho3+ concentrations and beta dose on TL intensity are two major aspects that have been investigated in detail. TL fading experiments were performed to determine dose storage capacity over a month after beta irradiation. Additionally, the various heating rate (VHR) experiments are conducted to determine the TL kinetic parameters. Besides, the glow curve deconvolution (GCD) for trap parameter determination is also applied, where the results obtained are comparable with the VHR results.

Noise equivalent temperature difference study of type-II superlattice MWIR focal plane arrays for high operating temperature performance

Achieving high operating temperature (HOT) plays a crucial role in miniaturizing type-II superlattice (T2SL) mid-wavelength infrared (MWIR) focal plane arrays (FPAs). However, their full potential has yet to be realized due to a lack of complete understanding of their operation from the perspective of detection principles. Here, by investigating the photon transmission path and optoelectronic performance of the simulated devices, a detailed noise equivalent temperature difference (NETD) model of the T2SL MWIR FPAs was established. The NETD limitations in the optics-limited and detector-limited modes were revealed by studying the effects of the source, optical system, and FPA-related parameters. Although NETD exhibits sensitivity to dark currents, improvements in the quantum efficiency and well capacity can further boost its performance. When the defects and carrier lifetimes are well controlled to completely suppress the dark current, the NETD of an MWIR system with optimized integration times, which operates between 150 K and 200 K, is predicted to be below 10 mK when detecting room-temperature targets. The results provide new insights into the model and sources contributing to the NETD and demonstrate the possibility of high-temperature operation of T2SLs MWIR FPAs.

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Research on two-dimensional material-based phototransistors has recently become a topic of great interest. However, the high number of design features, which impact the performance of these devices, and the multi-physical nature of the device operation make the accurate analysis of these devices a challenge. Here, we present a simple yet effective numerical framework to overcome this challenge. The one-dimensional framework is constructed on the drift-diffusion equations, Poisson’s equation, and wave propagation in multi-layered medium formalism. We apply this framework to study phototransistors made from monolayer molybdenum disulfide (MoS2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\hbox {MoS}}_{2}$$\\end{document}) placed on top of a back-gated silicon-oxide-coated silicon substrate. Numerical results, which show good agreement with the experimental results found in the literature, emphasize the necessity of including the inhomogeneous background for accurately calculating device metrics such as quantum efficiency and bandwidth. For the first time in literature, we calculate the phase noise of these phototransistors, which is a crucial performance metric for many applications where precise timing and synchronization are critical. We determine that applying a low drain-to-source voltage is the key requirement for low phase noise.

Influence of Drought Stress on the Rhizosphere Bacterial Community Structure of Cassava (Manihot esculenta Crantz).

Drought presents a significant abiotic stress that threatens crop productivity worldwide. Rhizosphere bacteria play pivotal roles in modulating plant growth and resilience to environmental stresses. Despite this, the extent to which rhizosphere bacteria are instrumental in plant responses to drought, and whether distinct cassava (Manihot esculenta Crantz) varieties harbor specific rhizosphere bacterial assemblages, remains unclear. In this study, we measured the growth and physiological characteristics, as well as the physical and chemical properties of the rhizosphere soil of drought-tolerant (SC124) and drought-sensitive (SC8) cassava varieties under conditions of both well-watered and drought stress. Employing 16S rDNA high-throughput sequencing, we analyzed the composition and dynamics of the rhizosphere bacterial community. Under drought stress, biomass, plant height, stem diameter, quantum efficiency of photosystem II (Fv/Fm), and soluble sugar of cassava decreased for both SC8 and SC124. The two varieties' rhizosphere bacterial communities' overall taxonomic structure was highly similar, but there were slight differences in relative abundance. SC124 mainly relied on Gamma-proteobacteria and Acidobacteriae in response to drought stress, and the abundance of this class was positively correlated with soil acid phosphatase. SC8 mainly relied on Actinobacteria in response to drought stress, and the abundance of this class was positively correlated with soil urease and soil saccharase. Overall, this study confirmed the key role of drought-induced rhizosphere bacteria in improving the adaptation of cassava to drought stress and clarified that this process is significantly related to variety.

Regulating the Photoisomerization of Covalent Organic Framework for Enhanced Photocatalytic Hydrogen Evolution†

Comprehensive SummaryCovalent organic framework (COF) is a desirable platform to tailor electronic properties for improving photocatalytic performances. However, the study on excited‐state configurations that determine photogenerated carrier dynamics has long been neglected. Herein, we concentrate on the molecular design of β‐ketoenamine‐linked COFs to drive their photoisomerization via the excited‐state intra‐molecular proton transfer (ESIPT), which can induce the partial keto‐to‐enol tautomerization and accordingly rearrange the photoinduced charge distribution. We demonstrate that the push‐pull electronic effect of functional side groups attached on the framework linkers is directly correlated with the ESIPT process. The phenylene linkers modified with electron‐withdrawing cyano‐groups reinforce the ESIPT‐induced tautomerization, leading to the in situ partial enolization for extended π‐conjugation and rearranged electron‐hole distribution. In contrast, the electron‐rich linkers limit the photoisomerization of COF and suppress the photoinduced electron accumulation. Thus, the maximum hydrogen evolution rate is achieved by the cyano‐modified COF, reaching as high as 162.72 mmol·g–1·h–1 with an apparent quantum efficiency of 13.44% at 475 nm, which is almost 11.5‐fold higher than those of analogous COFs with electron‐rich linkers. Our work opens up an avenue to control over the excited‐state structure transformation for enhanced photochemical applications.

In Situ Construction of Hollow Coral-Like Porous S-Doped g-C3N4/ZnIn2S4 S-Scheme Heterojunction for Efficient Photocatalytic Hydrogen Evolution.

The rational design of visible-light-responsive catalysts is crucial for converting solar energy into hydrogen energy to promote sustainable energy development. In this work, a C─S─C bond is introduced into g-C3N4 (CN) through S doping. With the help of the flexible C─S─C bond under specific stimuli, a hollow coral-like porous structure of S-doped g-C3N4 (S-CN) is synthesized for the first time. And an S-doped g-C3N4/ZnIn2S4 (S-CN/ZIS) heterojunction catalyst is in situ synthesized based on S-CN. S0.5-CN/ZIS exhibits excellent photocatalytic hydrogen evolution (PHE) efficiency (19.25mmol g-1 h-1), which is 2.7 times higher than that of the g-C3N4/ZnIn2S4 (CN/ZIS) catalyst (8.46mmol g-1 h-1), with a high surface quantum efficiency (AQE) of 34.43% at 420nm. Experiments and theoretical calculations demonstrate that the excellent photocatalytic performance is attributed to the larger specific surface area and porosity, enhanced interfacial electric field (IEF) effect, and appropriate hydrogen adsorption Gibbs free energy (ΔGH*). The synergistic effect of S doping and S-scheme heterojunction contributes to the above advancement. This study provides new insights and theoretical basis for the design of CN-based photocatalysts.

Enhanced near infrared and gate tunable photoresponse of MoSe2 transistor enabled by 2D hetero contact engineering

The excellent physical features of two-dimensional (2D) layered materials make them very promising for electronic and optoelectronic applications. Here, we investigated the gate-tunable and broadband (220, 365, 460, 510, 840 and 1020 nm) photoresponse of MoSe2 transistor with metallic (Cr–Au/MoSe2) and van der Waals (vdWs) hetero MoSe2/WTe2 contacts. Our study intends to investigate the underlying mechanism of photogeneration and carrier's transport process by Cr–Au/MoSe2 and hetero MoSe2/WTe2 contacts in the MoSe2 transistor. Since, our research revealed that MoSe2 devices with hetero MoSe2/WTe2 contacts exhibited remarkable performance, including high responsivity (R) of about 11.23 × 105 mA/W, exceptional external quantum efficiency (EQE) of 6.3 × 105 %, and detectivity (D*) of 4.61 × 1010 Jones compared to metallic contacts. This implies that the enhanced performance of our devices with 2D hetero-contacts could be attributed to reduced contact resistance, interlayer charge transfer and interlayer excitons in MoSe2/WTe2 heterostructure. Also, the gate-controlled response and broadband capabilities of van der Waals 2D heterostructures hold significant promises for a wide range of optoelectronic applications, including photodetectors, optical sensors, and visual imaging systems.

Steric hindrance induced low exciton binding energy enables low‐driving‐force organic solar cells

AbstractExciton binding energy (Eb) has been regarded as a critical parameter in charge separation during photovoltaic conversion. Minimizing the Eb of the photovoltaic materials can facilitate the exciton dissociation in low‐driving force organic solar cells (OSCs) and thus improve the power conversion efficiency (PCE); nevertheless, diminishing the Eb with deliberate design principles remains a significant challenge. Herein, bulky side chain as steric hindrance structure was inserted into Y‐series acceptors to minimize the Eb by modulating the intra‐ and intermolecular interaction. Theoretical and experimental results indicate that steric hindrance‐induced optimal intra‐ and intermolecular interaction can enhance molecular polarizability, promote electronic orbital overlap between molecules, and facilitate delocalized charge transfer pathways, thereby resulting in a low Eb. The conspicuously reduced Eb obtained in Y‐ChC5 with pinpoint steric hindrance modulation can minimize the detrimental effects on exciton dissociation in low‐driving‐force OSCs, achieving a remarkable PCE of 19.1% with over 95% internal quantum efficiency. Our study provides a new molecular design rationale to reduce the Eb.

Efficient Quasi-2D Perovskite Based Blue Light-Emitting Diodes with Carbon Dots Modified Hole Transport Layer.

Quasi-2D perovskites based blue light-emitting diodes (LEDs) suffer from its poor electroluminescence performance, mainly caused by the nonradiative recombination in in defect-rich low-n phases and the unbalanced hole-electron injection in the device. Here, we developed a highly efficient quasi-2D perovskite based sky-blue LEDs behaving recorded external quantum efficiency (EQE) of 21.07% by employing carbon dots (CDs) as additives in the hole transport layer (HTL). We ascribe the high EQE to the effective engineering of CDs: (1) The CDs at the interface of HTLs can suppress the formation of low-efficient n = 1 phase, resulting a high luminescence quantum yield and energy transfer efficiency of the mixed n-phase quasi-2D perovskites. (2) The CDs additives can reduce the conductivity of HTL, partially blocking the hole injection, and thus making more balanced hole-electron injection. The CDs-treated devices have excellent Spectral stability and enhanced operational stability and could be a new alternative additive in the perovskite optoelectronic devices.

Fabrication of broadband HgCdTe photodetectors with biomimetic insect corneal arrays

Broadband photodetectors are of great significance in a wide variety of technologically important areas. Inspired by bionics, insect cornea-mimicking microstructures could reduce surface reflection, thus enabling broadband detection. Here, we fabricate a broadband large-area (1280 × 1024) HgCdTe focal plane array photodetector based on biomimetic ZnS microarrays, which achieves high external quantum efficiency (> 60%, averaging 79%) across the broad wavelength range of 400 nm - 5000 nm. These results demonstrate that implementing biomimetic ZnS microstructures has effectively broadened the operational wavelength range of conventional HgCdTe infrared photodetectors to encompass the visible light spectrum. Our work achieves continuous visible-to-infrared spectral imaging and provides a beneficial route to fabricate broadband, large-area, high-performance photodetectors.