Fluorine(F)substitution in polymers modulates both molecular energy levels and film morphology;however,its impact on exciton–vibrational coupling and molecular reorganization energy is often neglected.Herein,we syste...Fluorine(F)substitution in polymers modulates both molecular energy levels and film morphology;however,its impact on exciton–vibrational coupling and molecular reorganization energy is often neglected.Herein,we systematically investigated F-modified polymers(PBTA-PSF,PBDB-PSF)and their nonfluorinated counterparts(PBTA-PS,PBDB-PS)through simulations and experiments.We found that F atoms effectively lower the vibrational frequency of the molecular skeleton and suppress exciton–vibration coupling,thereby reducing the nonradiative decay rate.Moreover,introducing F atoms significantly decreases the reorganization energy for the S_(0)→S_(1) and S_(0)→cation transitions while increasing the reorganization energy for the S_(1)→S_(0) and cation→S_(0) transitions.These changes facilitate exciton dissociation and reduce the energy loss caused by dissociation and nonradiative recombination of excitons.Additionally,introducing F atoms into polymers enhances theπ–πstacking strength and the crystal coherence length in both neat and blended films,ultimately resulting in improvements in the power conversion efficiency of PBTA-PSF:L8-BO and PBDB-PSF:L8-BO are 16.51%and 17.59%,respectively.This study provides valuable insights for designing organic semiconductor materials to minimize energy loss and achieve a higher power conversion efficiency.展开更多
N31-type phosphate laser glasses doped with different concentrations of Cu were prepared. Their optical loss coefficient at 1053 nm wavelength and nonradiative transition rate from the Nd3＋ 4F3/2 state were determine...N31-type phosphate laser glasses doped with different concentrations of Cu were prepared. Their optical loss coefficient at 1053 nm wavelength and nonradiative transition rate from the Nd3＋ 4F3/2 state were determined and analyzed in detail. The optical loss coefficient per unit of Cu2＋ （cm–1/ppmw） and the fluorescence decay rate （Hz/ppmw） caused by Cu2＋ and Nd3＋ interaction were 0.0024 and 7.9, respectively. Cu impurity affected both optical loss at 1053 nm and fluorescent emission of Nd3＋ 4F3/2 state seriously in N31 laser glass.展开更多
In this short review,we discuss a few recent advances in calculating the nonradiative decay rates for point defects in semiconductors.We briefly review the debates and connections of using different formalisms to calc...In this short review,we discuss a few recent advances in calculating the nonradiative decay rates for point defects in semiconductors.We briefly review the debates and connections of using different formalisms to calculate the multi-phonon processes.We connect Dr.Huang's formula with Marcus theory formula in the high temperature limit,and point out that Huang's formula provide an analytical expression for the phonon induced electron coupling constant in the Marcus theory formula.We also discussed the validity of 1D formula in dealing with the electron transition processes,and practical ways to correct the anharmonic effects.展开更多
The effects of irradiation of 1.0 MeV electrons on the n＋-p GaAs middle cell of GalnP/GaAs/Ge triple-junction solar cells are investigated by temperature-dependent photoluminescence （PL） measurements in the 10-300K...The effects of irradiation of 1.0 MeV electrons on the n＋-p GaAs middle cell of GalnP/GaAs/Ge triple-junction solar cells are investigated by temperature-dependent photoluminescence （PL） measurements in the 10-300K temperature range. The appearance of thermal quenching of the PL intensity with increasing temperature confirms the presence of a nonradiative recombination center in the cell after the electron irradiation, and the thermal activation energy of the center is determined using the Arrhenius plot of the PL intensity. Furthermore, by comparing the thermal activation and the ionization energies of the defects, the nonradiative recombination center in the n＋ p GaAs middle cell acting as a primary defect is identified as the E5 electron trap located at Ec - 0.96 eV.展开更多
Nonradiative recombination (NRR) centers in n-type GaN samples grown by MOCVD technique on a LT-GaN buffer layer and aAlN buffer layer have been studied by two wavelength excited photoluminescence (TWEPL). The near ba...Nonradiative recombination (NRR) centers in n-type GaN samples grown by MOCVD technique on a LT-GaN buffer layer and aAlN buffer layer have been studied by two wavelength excited photoluminescence (TWEPL). The near band-edge photoluminescence (PL) intensity decreases due to the superposition of below-gap excitation (BGE) light of energies 0.93, 1.17 and 1.27 eV over above-gap excitation (AGE) light of energy 4.66 eV. The decrease in PL intensity due to the addition of the BGE has been explained by a two levels recombination model based on SRH statistics. It indicates the presence of a pair of NRR centers in both samples, which are activated by the BGE. The degree of quenching in PL intensity for the sample grown on LT-GaN buffer layer is stronger than the sample grown on AlN buffer layer for all BGE sources. This result implies that the use of the AlN buffer layer is more effective for reducing the NRR centers in n-GaN layers than the LT-GaN buffer layer. The dependence of PL quenching on the AGE density, the BGE density and temperature has been also investigated. The NRR parameters have been quantitatively determined by solving rate equations and fitting the simulated results with the experimental data.展开更多
Comprehensive Summary The construction of luminescent two-dimensional(2D)imine-linked covalent organic frameworks(COFs)is a formidable challenge due to the strong interlayer stacking and bond rotations that typically ...Comprehensive Summary The construction of luminescent two-dimensional(2D)imine-linked covalent organic frameworks(COFs)is a formidable challenge due to the strong interlayer stacking and bond rotations that typically suppress intramolecular charge transfer(ICT),leading to nonradiative energy dissipation.Herein,three COFs with tailored interlayer distances and bond rotations are designed to modulate the ICT behaviours.The targeted COF(TPAZ-TPE-COF)achieved a significantly enhanced photoluminescence quantum yield(PLQY)of 21.22%in the solid state by restricting bond rotation and enlarging the layer distance.This represents a 3.5-fold and 530.5-fold improvement over TPAZ-PYTA-COF(6.15%),which has a shortened interlayer space,and TPAZ-PATA-COF(0.04%),which exhibits strong bond rotations,respectively.Importantly,TPAZ-TPE-COF also exhibits exceptional sensing performance for iron ions,with a detection limit at the ppb level.Both experimental and theoretical analyses reveal that the prominent luminescent performance of TPAZ-TPE-COF is assigned to the effective suppression of nonradiative pathways,especially those arising from interlayer stacking and bond vibrations.These findings pave the way for deliberate construction of imine-linked 2D COFs with high PL intensity,thereby expanding the portfolio of luminescent COFs with potential applications in sensing and optoelectronics.展开更多
A new ratiometric Boltzmann thermometry approach is presented for the narrow-line red-emitting bright phosphor Al_(0.993)Cr_(0.007)B_(4O6)N.It relies on thermalization between the two excited states^(2)E_(g)(^(2)G)and...A new ratiometric Boltzmann thermometry approach is presented for the narrow-line red-emitting bright phosphor Al_(0.993)Cr_(0.007)B_(4O6)N.It relies on thermalization between the two excited states^(2)E_(g)(^(2)G)and^(2)T_(1g)(^(2)G)of Cr^(3+)with an energy gap of 620 cm^(−1)for optimized thermometry at room temperature.It is shown that nonradiative coupling between these excited states is very fast,with rates in the order of severalµs^(−1).Due to the comparably slow radiative decay(k_(r)=0.033 ms^(−1))of the lowest excited^(2)E_(g)(^(2)G)state,the dynamic working range of this Boltzmann thermometer for the deep red spectral range is exceptionally wide,between<77 K and>873 K,even outperforming the classic workhorse example of Er^(3+).At temperatures above 340 K,also spectrally well-resolved broad-band emission due to the spin-allowed^(4)T_(2g)(^(4)F)→^(4)A_(2g)(^(4)F)transition is detectable,which simultaneously offers a possibility of very sensitive(S_(r)(500 K)>2%K^(−1))ratiometric Boltzmann-type crossover thermometry for higher temperatures.These findings imply that Al_(0.993)Cr_(0.007)B_(4)O_(6)N is a particularly robust and bright red luminescent thermometer with a record-breaking dynamic working range for a luminescent transition metal ion.展开更多
Organic photothermal materials based on conjugated structures hold great potential for solar harvesting but are often constrained by narrow absorption and limited solar-thermal conversion efficiency.A general molecula...Organic photothermal materials based on conjugated structures hold great potential for solar harvesting but are often constrained by narrow absorption and limited solar-thermal conversion efficiency.A general molecular design strategy that can simultaneously broaden absorption and enhance nonradiative decay remains elusive.Here,we pioneer a quinoid-donor-acceptor(Q-D-A)architecture specifically tailored for photothermal applications.Incorporating quinoidal unit into a D-A polymer backbone yields the novel polymer PAQM-TBz,which exhibits a reinforced backbone planarity,intensifiedπ-πinteractions,and enhanced diradical character compared with its D-A analogue,P2T-TBz.These synergistic features enable broadband absorption(400-1500 nm)and rapid nonradiative relaxation,yielding an outstanding photothermal conversion efficiency of 80.6%under 808 nm laser irradiation—nearly twice that of P2T-TBz.Under 1.0 kW m^(-2) simulated sunlight,PAQM-TBz achieves a record-high solar-to-vapor efficiency of 97.3%with an evaporation rate of 1.41 kg m^(-2) h^(-1).It also generates a peak thermoelectric voltage of 126.1 mV,and in integrated water-electricity cogeneration,attains an evaporation rate of 1.28 kg m^(-2) h^(-1) and a voltage 95.8 mV,ranking among the highest for organic materials.This work establishes the Q-D-A strategy as a transformative platform for advanced solar-thermal energy conversion and multifunctional solar-harvesting applications.展开更多
Nonradiative carrier recombinations at deep centers in semiconductors are of great importance for both fundamental physics and device engineering.In this article,we provide a revised analysis of Huang's original n...Nonradiative carrier recombinations at deep centers in semiconductors are of great importance for both fundamental physics and device engineering.In this article,we provide a revised analysis of Huang's original nonradiative multi-phonon(NMP)theory with ab initio calculations.First,we confirmed at the first-principles level that Huang's concise formula gives the same results as the matrix-based formula,and that Huang's high-temperature formula provides an analytical expression for the coupling constant in Marcus theory.Secondly,we correct for anharmonic effects by taking into account local phonon-mode variations for different charge states of a defect.The corrected capture rates for defects in GaN and SiC agree well with experiments.展开更多
It is well known that coumarin derivative is one of the important laser dyes in red-blue spectral range. There are many publications currently available on photophysical and photochemical properties of the coumarin de...It is well known that coumarin derivative is one of the important laser dyes in red-blue spectral range. There are many publications currently available on photophysical and photochemical properties of the coumarin derivative. It is evident from the results obtained that fluorescence lifetime and quantum yield of the coumarin derivative are very sensitive展开更多
Ternary strategy is one of the most effective methods to further boost the power conversion efficiency(PCE)of organic photovoltaic cells(OPVs).In terms of high-efficiency PM6:Y6 binary systems,there is still room to f...Ternary strategy is one of the most effective methods to further boost the power conversion efficiency(PCE)of organic photovoltaic cells(OPVs).In terms of high-efficiency PM6:Y6 binary systems,there is still room to further reduce energy_(loss)(E_(loss))through regulating molecular packing and aggregation by introducing a third component in the construction of ternary OPVs.Here we introduce a simple molecule BR1 based on an acceptor-donor-acceptor(A-D-A)structure with a wide bandgap and high crystallinity into PM6:Y6-based OPVs.It is proved that BR1 can be selectively dispersed into the donor phase in the PM6:Y6 and reduce disorder in the ternary blends,thus resulting in lower E_(loss,non-rad)and E_(loss).Furthermore,the mechanism study reveals well-develop phase separation morphology and complemented absorption spectra in the ternary blends,leading to higher charge mobility,suppressed recombination,which concurrently contributes to the significantly improved PCE of 17.23%for the ternary system compared with the binary ones(16.21%).This work provides an effective approach to improve the performance of the PM6:Y6-based OPVs by adopting a ternary strategy with a simple molecule as the third component.展开更多
Significant nonradiative energy loss and short exciton diffusion length in organic solar cells(OSCs)are two major obstacles to achieving state-of-the-art efficiencies.It is crucial to conduct a study on the intensive ...Significant nonradiative energy loss and short exciton diffusion length in organic solar cells(OSCs)are two major obstacles to achieving state-of-the-art efficiencies.It is crucial to conduct a study on the intensive mechanism and improvement strategies for future breakthroughs in the efficiency of OSCs.In this work,nonradiative energy loss and exciton diffusion length are optimized simultaneously by incorporating a vip acceptor(LA15)to construct ternary OSC(D18:L8-BO:LA15).Firstly,LA15 exhibits excellent compatibility with the host acceptor L8-BO,and effectively improves the fluorescence quantum efficiency(FLQY),resulting in suppressed non-radiative energy loss.Moreover,LA15 effectively prolongs the fluorescent lifetime of the acceptor phase from 0.85 to 1.12 ns,leading to larger exciton diffusion length,which is beneficial for reducing geminate recombination.Besides,the addition of LA15 optimizes the crystallinity of the active layer with amplified charge transport capacity.As a result,the optimized D18:L8-BO:LA15 device achieves ultralow nonradiative energy loss of 0.18 e V and improved fill factor(FF)with high efficiency up to 19.13%.These results highlight the crucial roles of regulating FLQYand exciton lifetime in achieving highefficiency OSCs.展开更多
The prevalent excitonic effects in low-dimensional semiconductors enable energy-transfer-initiated photocatalytic solar-to-chemical energy conversion.However,the generally strong interactions between excitons and latt...The prevalent excitonic effects in low-dimensional semiconductors enable energy-transfer-initiated photocatalytic solar-to-chemical energy conversion.However,the generally strong interactions between excitons and lattice vibrations in these low-dimensional systems lead to robust nonradiative energy loss,which inevitably impedes photocatalytic performance of energy-transfer-initiated reactions.Herein,we highlight the crucial role of engineering exciton-phonon interactions in suppressing nonradiative energy losses in low-dimensional semiconductor-based photocatalysts.By taking bismuth oxybromide(BiOBr)as an example,we demonstrate that phonon engineering could be effectively implemented by introducing Bi-Br vacancy clusters.Based on nonadiabatic molecular dynamics simulations and spectroscopic investigations,we demonstrate that the defective structure can promote exciton-low-frequency phonon coupling and reduce exciton-high-frequency optical phonon coupling.Benefiting from the tailored couplings,nonradiative decay of excitons in defective BiOBr is significantly suppressed,thereby facilitating exciton accumulation and hence energy-transfer-initiated photocatalysis.展开更多
Fisetin attracts intense attention not only due to its antioxidant and anticancer properties but also be-cause of wide applications in fluo-rescence probes and sensors,which are based on the dual fluorescence induced ...Fisetin attracts intense attention not only due to its antioxidant and anticancer properties but also be-cause of wide applications in fluo-rescence probes and sensors,which are based on the dual fluorescence induced by excited-state proton transfer(ESPT).However,to date,its ESPT dynamics remains unknown yet.In this study,we give a comprehensive investiga-tion on ESPT dynamics of fisetin in both protic methanol and aprot-ic acetonitrile by using femtosecond transient absorption spectroscopy combined with time-dependent density functional theory calculations.In acetonitrile,the ESPT time constant of fisetin is 1.2 ps.In methanol,two distinct intermolecular hydrogen bonding configurations contribute to a fast(<90 fs)and slow ESPT(11.1 ps),respectively.The slow ESPT in methanol explains the higher emission intensity of normal species than in acetonitrile.The ex-cited-state relaxation of fisetin involves two main vibrational modes:rotation between B and C rings and butterfly-like motion of C ring.Our results give insight into the effect of solvent-solute hydrogen bonding interaction on the dual fluorescence,providing a fundamental guide-line for the development of fluorescent probes and sensors based on ESPT.展开更多
Aggregation-induced emission luminogens(AIEgens)exhibit viscosity-responsive behavior resembling those of molecular rotors;however,their response mechanisms are more complex and cannot be adequately described using si...Aggregation-induced emission luminogens(AIEgens)exhibit viscosity-responsive behavior resembling those of molecular rotors;however,their response mechanisms are more complex and cannot be adequately described using simple rotational models.AIEgens demonstrate intricate dynamics that are highly dependent on their molecular structures.In this study,we synthesized water-soluble derivatives of representative AIEgens,including tetraphenylethene(TPE),bis(N,N-dialkylamino)anthracene(BDAA),and bridged stilbene,and systematically investigated the dependence of their photophysical properties in water/glycerol mixed solvents on temperature and viscosity.To elucidate the origin of their viscosity responsiveness,quantum chemical calculations were conducted to analyze their potential energy surfaces(PESs).The results revealed that compared to typical molecular rotors,these AIEgens exhibit significantly higher sensitivity to viscosity in low-viscosity regions.Notably,for TPE and BDAA derivatives,the viscosity responsiveness was found to be governed not by the activation energy barrier(ΔE_(a))based on the PES,but rather by the viscosity-dependent constraints on molecular structural changes.Furthermore,molecules possessing multiple aromatic rings or large,flexible,rotatable moieties were found to exhibit enhanced sensitivity to viscosity due to increased frictional interactions in solutions.This study provides critical insights into the mechanistic origins of the viscosity responsiveness of AIEgens,thereby advancing the fundamental understanding of their behavior and expanding their potential application as viscositysensitive probes.展开更多
Understanding and managing charge carrier recombination dynamics is crucial for optimizing the performance of metal halide perovskite optoelectronic devices.In this work,we introduce a machine learning-assisted intens...Understanding and managing charge carrier recombination dynamics is crucial for optimizing the performance of metal halide perovskite optoelectronic devices.In this work,we introduce a machine learning-assisted intensity-modulated two-photon photoluminescence microscopy approach for quantitatively mapping recombination processes in MAPbBr_(3) perovskite microcrystalline films at micrometer-scale resolution.To enhance model accuracy,a balanced classification sampling strategy was applied during the machine learning optimization stage.展开更多
The well crystalline YAG：Ce^3＋ phosphor was synthesized by sold-state method, and the temperature dependence of excitation and emission spectra of YAG：Ce^3＋ phosphor were investigated in the temperature range from...The well crystalline YAG：Ce^3＋ phosphor was synthesized by sold-state method, and the temperature dependence of excitation and emission spectra of YAG：Ce^3＋ phosphor were investigated in the temperature range from room temperature to 573 K. With temperature increasing, it was noted that the emission intensity of as-repared phosphors decreased considerably more rapidly when pumped by 460 nm than by 340 nm. The temperature-intensity curves under different excitation wavelengths were obtained using an Arrhenius function, and the corresponding activation energies were also obtained respectively. Thus, the experimental phenomenon was discussed in terms of nonradiative decay rate. The effects of as-prepared phosphors on the performance of the white LED with changing temperature were also studied.展开更多
Previous studies have found amplified warming over Europe-West Asia and Northeast Asia in summer since the mid- 1990s relative to elsewhere on the Eurasian continent, but the cause of the amplification in these two re...Previous studies have found amplified warming over Europe-West Asia and Northeast Asia in summer since the mid- 1990s relative to elsewhere on the Eurasian continent, but the cause of the amplification in these two regions remains unclear. In this study, we compared the individual contributions of influential factors for amplified warming over these two regions through a quantitative diagnostic analysis based on CFRAM (climate feedback-response analysis method). The changes in surface air temperature are decomposed into the partial changes due to radiative processes (including CO2 concentration, incident solar radiation at the top of the atmosphere, surface albedo, water vapor content, ozone concentration, and clouds) and non-radiative processes (including surface sensible heat flux, surface latent heat flux, and dynamical processes). Our results suggest that the enhanced warming over these two regions is primarily attributable to changes in the radiative processes, which contributed 0.62 and 0.98 K to the region-averaged warming over Europe-West Asia (1.00 K) and Northeast Asia (1.02 K), respectively. Among the radiative processes, the main drivers were clouds, CO2 concentration, and water vapor content. The cloud term alone contributed to the mean amplitude of warming by 0.40 and 0.85 K in Europe-West Asia and Northeast Asia, respectively. In comparison, the non-radiative processes made a much weaker contribution due to the combined impact of surface sensible heat flux, surface latent heat flux, and dynamical processes, accounting for only 0.38 K for the warming in Europe-West Asia and 0.05 K for the warming in Northeast Asia. The resemblance between the influential factors for the amplified warming in these two separate regions implies a common dynamical origin. Thus, this validates the possibility that they originate from the Silk Road pattern.展开更多
Optimizing the interfacial properties between perovskite and carbon electrodes has always been an important way to improve the photoelectric conversion efficiency(PCE)of carbon-based perovskite solar cells(C-PSCs)and ...Optimizing the interfacial properties between perovskite and carbon electrodes has always been an important way to improve the photoelectric conversion efficiency(PCE)of carbon-based perovskite solar cells(C-PSCs)and facilitate their commercialization.In this paper,nitrogen-doped graphene quantum dots(N-GQDs)with fluorescent properties were successfully prepared using inexpensive coal as raw material by a facile and environmentally friendly chemical reagent oxidation.The results show that the electron-rich pyridinic nitrogen in N-GQDs can act as Lewis bases to form coordination bonds with uncoordinated lead ions by sharing electron pairs,thereby reducing the defect density and nonradiative recombination of photo-generated electron-hole,and extending lifetime of charge carriers.In addition,due to the passivation of N-GQDs,the hysteresis effect of the device is significantly reduced and the long-term stability is also improved.By optimizing the concentration,the PCE of C-PSCs achieved a maximum of 14.31%,which was improved by 20.25%compared with 11.90%of the pristine C-PSCs.This work provides a facile,environmentally friendly and efficient strategy for improving the overall performance of C-PSCs using inexpensive coal-based N-GQDs.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.62027822)the National R&D Program of China(Grant No.2019YFA0706402).
文摘Fluorine(F)substitution in polymers modulates both molecular energy levels and film morphology;however,its impact on exciton–vibrational coupling and molecular reorganization energy is often neglected.Herein,we systematically investigated F-modified polymers(PBTA-PSF,PBDB-PSF)and their nonfluorinated counterparts(PBTA-PS,PBDB-PS)through simulations and experiments.We found that F atoms effectively lower the vibrational frequency of the molecular skeleton and suppress exciton–vibration coupling,thereby reducing the nonradiative decay rate.Moreover,introducing F atoms significantly decreases the reorganization energy for the S_(0)→S_(1) and S_(0)→cation transitions while increasing the reorganization energy for the S_(1)→S_(0) and cation→S_(0) transitions.These changes facilitate exciton dissociation and reduce the energy loss caused by dissociation and nonradiative recombination of excitons.Additionally,introducing F atoms into polymers enhances theπ–πstacking strength and the crystal coherence length in both neat and blended films,ultimately resulting in improvements in the power conversion efficiency of PBTA-PSF:L8-BO and PBDB-PSF:L8-BO are 16.51%and 17.59%,respectively.This study provides valuable insights for designing organic semiconductor materials to minimize energy loss and achieve a higher power conversion efficiency.
文摘N31-type phosphate laser glasses doped with different concentrations of Cu were prepared. Their optical loss coefficient at 1053 nm wavelength and nonradiative transition rate from the Nd3＋ 4F3/2 state were determined and analyzed in detail. The optical loss coefficient per unit of Cu2＋ （cm–1/ppmw） and the fluorescence decay rate （Hz/ppmw） caused by Cu2＋ and Nd3＋ interaction were 0.0024 and 7.9, respectively. Cu impurity affected both optical loss at 1053 nm and fluorescent emission of Nd3＋ 4F3/2 state seriously in N31 laser glass.
基金supported by the Director, Office of Science (SC), Basic Energy Science (BES)/Materials Science and Engineering Division (MSED) of the U.S. Department of Energy (DOE) under the Contract No. DE-AC02-05CH11231 through the Theory of Material project
文摘In this short review,we discuss a few recent advances in calculating the nonradiative decay rates for point defects in semiconductors.We briefly review the debates and connections of using different formalisms to calculate the multi-phonon processes.We connect Dr.Huang's formula with Marcus theory formula in the high temperature limit,and point out that Huang's formula provide an analytical expression for the phonon induced electron coupling constant in the Marcus theory formula.We also discussed the validity of 1D formula in dealing with the electron transition processes,and practical ways to correct the anharmonic effects.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11675020,11375028,11075018 and 10675023
文摘The effects of irradiation of 1.0 MeV electrons on the n＋-p GaAs middle cell of GalnP/GaAs/Ge triple-junction solar cells are investigated by temperature-dependent photoluminescence （PL） measurements in the 10-300K temperature range. The appearance of thermal quenching of the PL intensity with increasing temperature confirms the presence of a nonradiative recombination center in the cell after the electron irradiation, and the thermal activation energy of the center is determined using the Arrhenius plot of the PL intensity. Furthermore, by comparing the thermal activation and the ionization energies of the defects, the nonradiative recombination center in the n＋ p GaAs middle cell acting as a primary defect is identified as the E5 electron trap located at Ec - 0.96 eV.
文摘Nonradiative recombination (NRR) centers in n-type GaN samples grown by MOCVD technique on a LT-GaN buffer layer and aAlN buffer layer have been studied by two wavelength excited photoluminescence (TWEPL). The near band-edge photoluminescence (PL) intensity decreases due to the superposition of below-gap excitation (BGE) light of energies 0.93, 1.17 and 1.27 eV over above-gap excitation (AGE) light of energy 4.66 eV. The decrease in PL intensity due to the addition of the BGE has been explained by a two levels recombination model based on SRH statistics. It indicates the presence of a pair of NRR centers in both samples, which are activated by the BGE. The degree of quenching in PL intensity for the sample grown on LT-GaN buffer layer is stronger than the sample grown on AlN buffer layer for all BGE sources. This result implies that the use of the AlN buffer layer is more effective for reducing the NRR centers in n-GaN layers than the LT-GaN buffer layer. The dependence of PL quenching on the AGE density, the BGE density and temperature has been also investigated. The NRR parameters have been quantitatively determined by solving rate equations and fitting the simulated results with the experimental data.
基金the National Natural Science Foundation of China(52303288,22075309,22378413,22161132010)National Key R&D Program of China Ministry of Science and Technology(2024YFE0206900)+4 种基金Science and Technology Innovation Plan of the Science and Technology Commission of Shanghai Municipality(22ZR1470100,23DZ1202600,23DZ1201804)the Youth Innovation Promotion Association of Chinese Academy of Sciences(E324441401)Biomaterials and Regenerative Medicine Institute Cooperative Research Project Shanghai Jiao Tong University School of Medicine(2022LHA09)Dr.Y.Fu gratefully acknowledge the GWK support for funding this project by providing computing time through the Center for Information Services and HPC(ZIH)at TU DresdenDr.S.Bi thanks the financial support by a fellowship award from the Research Grants Council of the Hong Kong Special Administrative Region,China(Project No.CityU PDFS2324-1S08).
文摘Comprehensive Summary The construction of luminescent two-dimensional(2D)imine-linked covalent organic frameworks(COFs)is a formidable challenge due to the strong interlayer stacking and bond rotations that typically suppress intramolecular charge transfer(ICT),leading to nonradiative energy dissipation.Herein,three COFs with tailored interlayer distances and bond rotations are designed to modulate the ICT behaviours.The targeted COF(TPAZ-TPE-COF)achieved a significantly enhanced photoluminescence quantum yield(PLQY)of 21.22%in the solid state by restricting bond rotation and enlarging the layer distance.This represents a 3.5-fold and 530.5-fold improvement over TPAZ-PYTA-COF(6.15%),which has a shortened interlayer space,and TPAZ-PATA-COF(0.04%),which exhibits strong bond rotations,respectively.Importantly,TPAZ-TPE-COF also exhibits exceptional sensing performance for iron ions,with a detection limit at the ppb level.Both experimental and theoretical analyses reveal that the prominent luminescent performance of TPAZ-TPE-COF is assigned to the effective suppression of nonradiative pathways,especially those arising from interlayer stacking and bond vibrations.These findings pave the way for deliberate construction of imine-linked 2D COFs with high PL intensity,thereby expanding the portfolio of luminescent COFs with potential applications in sensing and optoelectronics.
基金support by the“Young College”of the North-Rhine Westphalian Academy of Science,Humanities,and the Arts.Generous funding by the German National Science Foundation(DFG,SU 1156/5-1,project no.554302036)and the Strategic Research Fund of the HHU Düsseldorf is also gratefully acknowledged.
文摘A new ratiometric Boltzmann thermometry approach is presented for the narrow-line red-emitting bright phosphor Al_(0.993)Cr_(0.007)B_(4O6)N.It relies on thermalization between the two excited states^(2)E_(g)(^(2)G)and^(2)T_(1g)(^(2)G)of Cr^(3+)with an energy gap of 620 cm^(−1)for optimized thermometry at room temperature.It is shown that nonradiative coupling between these excited states is very fast,with rates in the order of severalµs^(−1).Due to the comparably slow radiative decay(k_(r)=0.033 ms^(−1))of the lowest excited^(2)E_(g)(^(2)G)state,the dynamic working range of this Boltzmann thermometer for the deep red spectral range is exceptionally wide,between<77 K and>873 K,even outperforming the classic workhorse example of Er^(3+).At temperatures above 340 K,also spectrally well-resolved broad-band emission due to the spin-allowed^(4)T_(2g)(^(4)F)→^(4)A_(2g)(^(4)F)transition is detectable,which simultaneously offers a possibility of very sensitive(S_(r)(500 K)>2%K^(−1))ratiometric Boltzmann-type crossover thermometry for higher temperatures.These findings imply that Al_(0.993)Cr_(0.007)B_(4)O_(6)N is a particularly robust and bright red luminescent thermometer with a record-breaking dynamic working range for a luminescent transition metal ion.
基金supported by the National Natural Science Foundation of China(52363021 and 22305050)Science and Technology Foundation of Guizhou Province(QKHJC-ZK[2024]Key 002).
文摘Organic photothermal materials based on conjugated structures hold great potential for solar harvesting but are often constrained by narrow absorption and limited solar-thermal conversion efficiency.A general molecular design strategy that can simultaneously broaden absorption and enhance nonradiative decay remains elusive.Here,we pioneer a quinoid-donor-acceptor(Q-D-A)architecture specifically tailored for photothermal applications.Incorporating quinoidal unit into a D-A polymer backbone yields the novel polymer PAQM-TBz,which exhibits a reinforced backbone planarity,intensifiedπ-πinteractions,and enhanced diradical character compared with its D-A analogue,P2T-TBz.These synergistic features enable broadband absorption(400-1500 nm)and rapid nonradiative relaxation,yielding an outstanding photothermal conversion efficiency of 80.6%under 808 nm laser irradiation—nearly twice that of P2T-TBz.Under 1.0 kW m^(-2) simulated sunlight,PAQM-TBz achieves a record-high solar-to-vapor efficiency of 97.3%with an evaporation rate of 1.41 kg m^(-2) h^(-1).It also generates a peak thermoelectric voltage of 126.1 mV,and in integrated water-electricity cogeneration,attains an evaporation rate of 1.28 kg m^(-2) h^(-1) and a voltage 95.8 mV,ranking among the highest for organic materials.This work establishes the Q-D-A strategy as a transformative platform for advanced solar-thermal energy conversion and multifunctional solar-harvesting applications.
基金supported by the National Natural Science Foundation of China (Grand Nos. 61927901, 11674241, 11574304, and 11774338)supported by the Director, Office of Science (SC), Basic Energy Science (BES)/Materials Science and Engineering Division (MSED) of the US Department of Energy (DOE) (Grant No. DE-AC02-05CH11231) through the Theory of Material project
文摘Nonradiative carrier recombinations at deep centers in semiconductors are of great importance for both fundamental physics and device engineering.In this article,we provide a revised analysis of Huang's original nonradiative multi-phonon(NMP)theory with ab initio calculations.First,we confirmed at the first-principles level that Huang's concise formula gives the same results as the matrix-based formula,and that Huang's high-temperature formula provides an analytical expression for the coupling constant in Marcus theory.Secondly,we correct for anharmonic effects by taking into account local phonon-mode variations for different charge states of a defect.The corrected capture rates for defects in GaN and SiC agree well with experiments.
文摘It is well known that coumarin derivative is one of the important laser dyes in red-blue spectral range. There are many publications currently available on photophysical and photochemical properties of the coumarin derivative. It is evident from the results obtained that fluorescence lifetime and quantum yield of the coumarin derivative are very sensitive
基金This work was financially supported by the National Natural Science Foundation of China(Nos.22005234 and 61904134)Zhejiang Lab(No.2021MC0AB02).
文摘Ternary strategy is one of the most effective methods to further boost the power conversion efficiency(PCE)of organic photovoltaic cells(OPVs).In terms of high-efficiency PM6:Y6 binary systems,there is still room to further reduce energy_(loss)(E_(loss))through regulating molecular packing and aggregation by introducing a third component in the construction of ternary OPVs.Here we introduce a simple molecule BR1 based on an acceptor-donor-acceptor(A-D-A)structure with a wide bandgap and high crystallinity into PM6:Y6-based OPVs.It is proved that BR1 can be selectively dispersed into the donor phase in the PM6:Y6 and reduce disorder in the ternary blends,thus resulting in lower E_(loss,non-rad)and E_(loss).Furthermore,the mechanism study reveals well-develop phase separation morphology and complemented absorption spectra in the ternary blends,leading to higher charge mobility,suppressed recombination,which concurrently contributes to the significantly improved PCE of 17.23%for the ternary system compared with the binary ones(16.21%).This work provides an effective approach to improve the performance of the PM6:Y6-based OPVs by adopting a ternary strategy with a simple molecule as the third component.
基金supported by the National Natural Science Foundation of China(22309098,62305350,22375213)Shandong Natural Science Foundation(ZR2022QF024)+1 种基金the Youth Innovation Promotion Association CAS(2021211)Shandong Energy Institute(SEIS202108)。
文摘Significant nonradiative energy loss and short exciton diffusion length in organic solar cells(OSCs)are two major obstacles to achieving state-of-the-art efficiencies.It is crucial to conduct a study on the intensive mechanism and improvement strategies for future breakthroughs in the efficiency of OSCs.In this work,nonradiative energy loss and exciton diffusion length are optimized simultaneously by incorporating a vip acceptor(LA15)to construct ternary OSC(D18:L8-BO:LA15).Firstly,LA15 exhibits excellent compatibility with the host acceptor L8-BO,and effectively improves the fluorescence quantum efficiency(FLQY),resulting in suppressed non-radiative energy loss.Moreover,LA15 effectively prolongs the fluorescent lifetime of the acceptor phase from 0.85 to 1.12 ns,leading to larger exciton diffusion length,which is beneficial for reducing geminate recombination.Besides,the addition of LA15 optimizes the crystallinity of the active layer with amplified charge transport capacity.As a result,the optimized D18:L8-BO:LA15 device achieves ultralow nonradiative energy loss of 0.18 e V and improved fill factor(FF)with high efficiency up to 19.13%.These results highlight the crucial roles of regulating FLQYand exciton lifetime in achieving highefficiency OSCs.
基金Thisworkwas supported by the National Key R&DProgram of China(no.2019YFA0210004)the Strategic Priority Research Program of Chinese Academy of Sciences(no.XDB36000000)+3 种基金the National Natural Science Foundation of China(nos.21922509,21905262,21890754,T2122004,9216310512074266,11620101003,11974322,U2032212,and U2032160)the Anhui Provincial Natural Science Foundation(no.2108085J07)the University Synergy Innovation Program of Anhui Province(nos.GXXT-2020-005 and GXXT-2021-020)the Science and Technology Project of Shenzhen(grant no.20200802180159001).
文摘The prevalent excitonic effects in low-dimensional semiconductors enable energy-transfer-initiated photocatalytic solar-to-chemical energy conversion.However,the generally strong interactions between excitons and lattice vibrations in these low-dimensional systems lead to robust nonradiative energy loss,which inevitably impedes photocatalytic performance of energy-transfer-initiated reactions.Herein,we highlight the crucial role of engineering exciton-phonon interactions in suppressing nonradiative energy losses in low-dimensional semiconductor-based photocatalysts.By taking bismuth oxybromide(BiOBr)as an example,we demonstrate that phonon engineering could be effectively implemented by introducing Bi-Br vacancy clusters.Based on nonadiabatic molecular dynamics simulations and spectroscopic investigations,we demonstrate that the defective structure can promote exciton-low-frequency phonon coupling and reduce exciton-high-frequency optical phonon coupling.Benefiting from the tailored couplings,nonradiative decay of excitons in defective BiOBr is significantly suppressed,thereby facilitating exciton accumulation and hence energy-transfer-initiated photocatalysis.
基金supported by the National Natural Science Foundation of China(No.22003066)。
文摘Fisetin attracts intense attention not only due to its antioxidant and anticancer properties but also be-cause of wide applications in fluo-rescence probes and sensors,which are based on the dual fluorescence induced by excited-state proton transfer(ESPT).However,to date,its ESPT dynamics remains unknown yet.In this study,we give a comprehensive investiga-tion on ESPT dynamics of fisetin in both protic methanol and aprot-ic acetonitrile by using femtosecond transient absorption spectroscopy combined with time-dependent density functional theory calculations.In acetonitrile,the ESPT time constant of fisetin is 1.2 ps.In methanol,two distinct intermolecular hydrogen bonding configurations contribute to a fast(<90 fs)and slow ESPT(11.1 ps),respectively.The slow ESPT in methanol explains the higher emission intensity of normal species than in acetonitrile.The ex-cited-state relaxation of fisetin involves two main vibrational modes:rotation between B and C rings and butterfly-like motion of C ring.Our results give insight into the effect of solvent-solute hydrogen bonding interaction on the dual fluorescence,providing a fundamental guide-line for the development of fluorescent probes and sensors based on ESPT.
基金JSPS Research Fellowships for Young Scientistssupported in part by JST SPRING,Japan(Nos.JPMJSP2106 and JPMJSP2180,Takuya Tanaka.and Yuki Sawatari.)+1 种基金MEXT/JSPS KAKENHI grants(No.23H02036,Gen-ichi Konishi)Murata Science and Education Foundation(Gen-ichi Konishi)。
文摘Aggregation-induced emission luminogens(AIEgens)exhibit viscosity-responsive behavior resembling those of molecular rotors;however,their response mechanisms are more complex and cannot be adequately described using simple rotational models.AIEgens demonstrate intricate dynamics that are highly dependent on their molecular structures.In this study,we synthesized water-soluble derivatives of representative AIEgens,including tetraphenylethene(TPE),bis(N,N-dialkylamino)anthracene(BDAA),and bridged stilbene,and systematically investigated the dependence of their photophysical properties in water/glycerol mixed solvents on temperature and viscosity.To elucidate the origin of their viscosity responsiveness,quantum chemical calculations were conducted to analyze their potential energy surfaces(PESs).The results revealed that compared to typical molecular rotors,these AIEgens exhibit significantly higher sensitivity to viscosity in low-viscosity regions.Notably,for TPE and BDAA derivatives,the viscosity responsiveness was found to be governed not by the activation energy barrier(ΔE_(a))based on the PES,but rather by the viscosity-dependent constraints on molecular structural changes.Furthermore,molecules possessing multiple aromatic rings or large,flexible,rotatable moieties were found to exhibit enhanced sensitivity to viscosity due to increased frictional interactions in solutions.This study provides critical insights into the mechanistic origins of the viscosity responsiveness of AIEgens,thereby advancing the fundamental understanding of their behavior and expanding their potential application as viscositysensitive probes.
基金financial support from Swedish Energy Agency grant 50709-1Swedish Research Council grant 2021-05207+2 种基金KAW WISE/WASP grant 01-22Olle Engkvist foundation grant 235-0422Light and Materials profile area at Lund University(Young Investigator Synergy Award,2023)。
文摘Understanding and managing charge carrier recombination dynamics is crucial for optimizing the performance of metal halide perovskite optoelectronic devices.In this work,we introduce a machine learning-assisted intensity-modulated two-photon photoluminescence microscopy approach for quantitatively mapping recombination processes in MAPbBr_(3) perovskite microcrystalline films at micrometer-scale resolution.To enhance model accuracy,a balanced classification sampling strategy was applied during the machine learning optimization stage.
基金the Key Technologies R&D Program of Shandong Province (2006gg2201014)Tianjin Natural Science Foundation (07JCYBJC06400)Tianjin Education Committee Science and Technology Development Foundation
文摘The well crystalline YAG：Ce^3＋ phosphor was synthesized by sold-state method, and the temperature dependence of excitation and emission spectra of YAG：Ce^3＋ phosphor were investigated in the temperature range from room temperature to 573 K. With temperature increasing, it was noted that the emission intensity of as-repared phosphors decreased considerably more rapidly when pumped by 460 nm than by 340 nm. The temperature-intensity curves under different excitation wavelengths were obtained using an Arrhenius function, and the corresponding activation energies were also obtained respectively. Thus, the experimental phenomenon was discussed in terms of nonradiative decay rate. The effects of as-prepared phosphors on the performance of the white LED with changing temperature were also studied.
基金supported by the National Key Research and Development Program of China(Grant Nos.2018YFA0606403 and 2015CB453202)the National Natural Science Foundation of China(Grant Nos.41790473 and 41421004)
文摘Previous studies have found amplified warming over Europe-West Asia and Northeast Asia in summer since the mid- 1990s relative to elsewhere on the Eurasian continent, but the cause of the amplification in these two regions remains unclear. In this study, we compared the individual contributions of influential factors for amplified warming over these two regions through a quantitative diagnostic analysis based on CFRAM (climate feedback-response analysis method). The changes in surface air temperature are decomposed into the partial changes due to radiative processes (including CO2 concentration, incident solar radiation at the top of the atmosphere, surface albedo, water vapor content, ozone concentration, and clouds) and non-radiative processes (including surface sensible heat flux, surface latent heat flux, and dynamical processes). Our results suggest that the enhanced warming over these two regions is primarily attributable to changes in the radiative processes, which contributed 0.62 and 0.98 K to the region-averaged warming over Europe-West Asia (1.00 K) and Northeast Asia (1.02 K), respectively. Among the radiative processes, the main drivers were clouds, CO2 concentration, and water vapor content. The cloud term alone contributed to the mean amplitude of warming by 0.40 and 0.85 K in Europe-West Asia and Northeast Asia, respectively. In comparison, the non-radiative processes made a much weaker contribution due to the combined impact of surface sensible heat flux, surface latent heat flux, and dynamical processes, accounting for only 0.38 K for the warming in Europe-West Asia and 0.05 K for the warming in Northeast Asia. The resemblance between the influential factors for the amplified warming in these two separate regions implies a common dynamical origin. Thus, this validates the possibility that they originate from the Silk Road pattern.
基金financially supported by the National Natural Science Foundation of China(52162035)the Open project of State Key Laboratory of Fine Chemicals,the Dalian University of Technology(KF2004)the Graduate Research Innovation Project of Xinjiang Uyghur Autonomous Region(XJ2022G045)。
文摘Optimizing the interfacial properties between perovskite and carbon electrodes has always been an important way to improve the photoelectric conversion efficiency(PCE)of carbon-based perovskite solar cells(C-PSCs)and facilitate their commercialization.In this paper,nitrogen-doped graphene quantum dots(N-GQDs)with fluorescent properties were successfully prepared using inexpensive coal as raw material by a facile and environmentally friendly chemical reagent oxidation.The results show that the electron-rich pyridinic nitrogen in N-GQDs can act as Lewis bases to form coordination bonds with uncoordinated lead ions by sharing electron pairs,thereby reducing the defect density and nonradiative recombination of photo-generated electron-hole,and extending lifetime of charge carriers.In addition,due to the passivation of N-GQDs,the hysteresis effect of the device is significantly reduced and the long-term stability is also improved.By optimizing the concentration,the PCE of C-PSCs achieved a maximum of 14.31%,which was improved by 20.25%compared with 11.90%of the pristine C-PSCs.This work provides a facile,environmentally friendly and efficient strategy for improving the overall performance of C-PSCs using inexpensive coal-based N-GQDs.
