Radiation protection programs aims to reduce the radiation dose to the lowest possible level under the Dose Limit (DL) limit by the national or international laws, while the dose monitoring programs working as scale u...Radiation protection programs aims to reduce the radiation dose to the lowest possible level under the Dose Limit (DL) limit by the national or international laws, while the dose monitoring programs working as scale used to evaluating the efficiency of these programs and tools. In this study, the average of the annual Eff dose for the intensive care units at Hamad General Hospital (HGH) is less than the 50% of DL. It was aiming also to evaluate the efficiency of the radiation safety requirements (especially the shielding Adequacy) for the non radiation workers at oncology centers, hence several monitors were installed in chosen locations outside the radiation treatment machine from 2007 to 2011.展开更多
In this thesis,we consider the existence of solutions for the following mixed dispersion nonlinear Schrödinger equation■where is a continuous function,,.We shall prove that(1)has multiple non-radial solutions by...In this thesis,we consider the existence of solutions for the following mixed dispersion nonlinear Schrödinger equation■where is a continuous function,,.We shall prove that(1)has multiple non-radial solutions by variational method.This paper provides a method to prove compactness for the study of the mixed dispersion nonlinear Schrödinger equation with quasilinear terms.展开更多
Ternary blending as one of the most successful strategies has achieved continuous performance breakthroughs in organic solar cells(OSCs)over the past few years.Here,a small molecule featuring a dithieno[3,2-f:2′,3′-...Ternary blending as one of the most successful strategies has achieved continuous performance breakthroughs in organic solar cells(OSCs)over the past few years.Here,a small molecule featuring a dithieno[3,2-f:2′,3′-h]phthalimide derivative as the intermediate unit,named DTP-C8-R,is designed and utilized as the third component to construct ternary OSCs(TOSCs).The increased molecular packing of L8-BO as well as the charge transfer excitons between PM6 and DTP-C8-R lead to a very low nonradiative energy loss of 0.179 eV and a high open-circuit voltage(V_(OC))of 0.910 V in the TOSCs based on the PM6:L8-BO host blend.Moreover,the DTP-C8-R:PM6:L8-BO film(0.05:0.95:1.2,w/w)possesses better fibrous nanophase separation and the enhancedπ-πstacking ordering of the acceptors with a larger crystal coherence length compared with the PM6:L8-BO blend film,so the TOSCs present more efficient exciton dissociation,longer carrier lifetime,faster carrier transport and less charge recombination.It boosts the power conversion efficiency to 19.22%with a short-circuit current density of 27.10 mA cm^(-2).This work demonstrates that the small molecule based on a dithieno[3,2-f:2′,3′-h]phthalimide derivative as the minor component is an executable strategy to achieve high-performance TOSCs with high V_(OC).展开更多
With regard to micro-light-emitting diodes(micro-LEDs),their excellent brightness,low energy consumption,and ultrahigh resolution are significant advantages.However,the large size of traditional inorganic phosphors an...With regard to micro-light-emitting diodes(micro-LEDs),their excellent brightness,low energy consumption,and ultrahigh resolution are significant advantages.However,the large size of traditional inorganic phosphors and the number of side defects have restricted the practical applications of small sized micro-LEDs.Recently,quantum dot(QD)and nonradiative energy transfer(NRET)have been proposed to solve existing problems.QDs possess nanoscale dimensions and high luminous efficiency,and they are suitable for NRET because they are able to nearly contact the micro-LED chip.The NRET between QDs and micro-LED chip further improves the color conversion efficiency(CCE)and effective quantum yield(EQY)of full-color micro-LED devices.In this review,we discuss the NRET mechanism for QD micro-LED devices,and then nano-pillar LED,nano-hole LED,and nano-ring LED are introduced in detail.These structures are beneficial to the NRET between QD and micro-LED,especially nano-ring LED.Finally,the challenges and future envisions have also been described.展开更多
This study presents experimental evidence of the dependence of non-radiative recombination processes on the electron-phonon coupling of perovskite in perovskite solar cells(PSCs).Via A-site cation engineering,a weaker...This study presents experimental evidence of the dependence of non-radiative recombination processes on the electron-phonon coupling of perovskite in perovskite solar cells(PSCs).Via A-site cation engineering,a weaker electron-phonon coupling in perovskite has been achieved by introducing the structurally soft cyclohexane methylamine(CMA^(+))cation,which could serve as a damper to alleviate the mechanical stress caused by lattice oscillations,compared to the rigid phenethyl methylamine(PEA^(+))analog.It demonstrates a significantly lower non-radiative recombination rate,even though the two types of bulky cations have similar chemical passivation effects on perovskite,which might be explained by the suppressed carrier capture process and improved lattice geometry relaxation.The resulting PSCs achieve an exceptional power conversion efficiency(PCE)of 25.5%with a record-high opencircuit voltage(V_(OC))of 1.20 V for narrow bandgap perovskite(FAPbI_(3)).The established correlations between electron-phonon coupling and non-radiative decay provide design and screening criteria for more effective passivators for highly efficient PSCs approaching the Shockley-Queisser limit.展开更多
Analytical expressions are given for computing the magnetic potential and charac-teristic functions produced by the non-radial deflectors.These expressions are useful for designingthe defiectors such as those used in ...Analytical expressions are given for computing the magnetic potential and charac-teristic functions produced by the non-radial deflectors.These expressions are useful for designingthe defiectors such as those used in the color picture tubes and the electron beam lithographysystem.The computing results are in agreement with the measured values.展开更多
The heavy-atom effect of halogen(Br and I)has been widely employed for boosting spin-crossover in organic molecules,while recent investigation indicated halogen-substitution can also enhance fluorescence and even lead...The heavy-atom effect of halogen(Br and I)has been widely employed for boosting spin-crossover in organic molecules,while recent investigation indicated halogen-substitution can also enhance fluorescence and even lead to aggregation-induced emission(AIE).In this work,we investigated ultrafast excited state dynamics of a halogen-substituted model system,i.e.squaryliums NSQ-R(R=H,Cl,Br,I),by using femtosecond spectroscopy and theoretical approach.Fast external reorganization(Ex-re,~3 ps)and slow internal reorganization(In-re,5-20 ps)were observed,while quantitative fitting indicated halogen-substitution leads to a slower non-radiative S1→S0 decay(k_(NR)^(s))and subsequently enhanced fluorescence emitting.By analyzing the extracted k_(NR)^(s)within theoretical framework of non-radiative transition in the strong coupling regime,a plausible AIE mechanism of NSQs was revealed.Our work provides a clear picture on non-radiative dynamics of halogen-substituted squaryliums,which might be useful for future development of organic dyes.展开更多
The presence of SnZn-related defects in Cu_(2)ZnSn(S,Se)_(4)(CZTSSe)absorber results in large irreversible energy loss and extra irreversible electron-hole non-radiative recombination,thus hindering the efficiency enh...The presence of SnZn-related defects in Cu_(2)ZnSn(S,Se)_(4)(CZTSSe)absorber results in large irreversible energy loss and extra irreversible electron-hole non-radiative recombination,thus hindering the efficiency enhancement of CZTSSe devices.Although the incorporation of Ag in CZTSSe can effectively suppress the SnZn-related defects and significantly improve the resulting cell performance,an excellent efficiency has not been achieved to date primarily owing to the poor electrical-conductivity and the low carrier density of the CZTSSe film induced by Ag substitution.Herein,this study exquisitely devises an Ag/H co-doping strategy in CZTSSe absorber via Ag substitution programs followed by hydrogen-plasma treatment procedure to suppress SnZn defects for achieving efficient CZTSSe devices.In-depth investigation results demonstrate that the incorporation of H in Ag-based CZTSSe absorber is expected to improve the poor electrical-conductivity and the low carrier density caused by Ag substitution.Importantly,the C=O and O-H functional groups induced by hydrogen incorporation,serving as an electron donor,can interact with under-coordinated cations in CZTSSe material,effectively passivating the SnZn-related defects.Consequently,the incorporation of an appropriate amount of Ag/H in CZTSSe mitigates carrier non-radiative recombination,prolongs minority carrier lifetime,and thus yields a champion efficiency of 14.74%,showing its promising application in kesterite-based CZTSSe devices.展开更多
Room-temperature phosphorescence（RTP） materials have attracted great attention due to their involvement of excited triplet states and comparatively long decay lifetimes.In this short review,recent progress on enhanc...Room-temperature phosphorescence（RTP） materials have attracted great attention due to their involvement of excited triplet states and comparatively long decay lifetimes.In this short review,recent progress on enhancement of RTP from purely organic materials is summarized.According to the mechanism of phosphorescence emission,two principles are discussed to construct efficient RTP materials：one is promoting intersystem crossing（ISC） efficiency by using aromatic carbonyl,heavyatom,or/and heterocycle/heteroatom containing compounds;the other is suppressing intramolecular motion and intermolecular collision which can quench excited triplet states,including embedding phosphors into polymers and packing them tightly in crystals.With aforementioned strategies,RTP from purely organic materials was achieved both in fluid and rigid media.展开更多
Room temperature phosphorescence(RTP) has drawn increasing attention for its great potential in practical applications.Polymers with large molecular weights and long chains tend to form coil, which can endow them with...Room temperature phosphorescence(RTP) has drawn increasing attention for its great potential in practical applications.Polymers with large molecular weights and long chains tend to form coil, which can endow them with a high degree of possible rigidity and result in the much restricted non-radiative transition. Also, the intertwined structure of polymers could isolate the oxygen and humidity effectively, thus reducing the consumption of triplet excitons. In consideration of these points, organic polymers would be another kind of ideal platform to realize RTP effect. This short review summarized the design strategy of the purely organic room temperature phosphorescence polymers, mainly focusing on the building forms of polymers and the corresponding inherent mechanisms,and also gives some outlooks on the further exploration of this field at the end of this paper.展开更多
The passivation of non-radiative states and inhibition of band tailings are desirable for improving the open-circuit voltage(V_(oc))of CZTSSe thin-film solar cells.Recently,alkali metal doping has been investigated to...The passivation of non-radiative states and inhibition of band tailings are desirable for improving the open-circuit voltage(V_(oc))of CZTSSe thin-film solar cells.Recently,alkali metal doping has been investigated to passivate defects in CZTSSe films.Herein,we investigate Li doping effects by applying Li OH into CZTSSe precursor solutions,and verify that carrier transport is enhanced in the CZTSSe solar cells.Systematic characterizations demonstrate that Li doping can effectively passivate non-radiative recombination centers and reduce band tailings of the CZTSSe films,leading to the decrease in total defect density and the increase in separation distance between donor and acceptor.Fewer free carriers are trapped in the band tail states,which speeds up carrier transport and reduces the probability of deep-level defects capturing carriers.The charge recombination lifetime is about twice as long as that of the undoped CZTSSe device,implying the heterojunction interface recombination is also inhibited.Besides,Li doping can increase carrier concentration and enhance build-in voltage,leading to a better carrier collection.By adjusting the Li/(Li+Cu)ratio to 18%,the solar cell efficiency is increased significantly to 9.68%with the fill factor(FF)of 65.94%,which is the highest FF reported so far for the flexible CZTSSe solar cells.The increased efficiency is mainly attributed to the reduction of V_(oc)deficit and the improved CZTSSe/Cd S junction quality.These results open up a simple route to passivate non-radiative states and reduce the band tailings of the CZTSSe films and improve the efficiency of the flexible CZTSSe solar cells.展开更多
Solution-processed metal halide perovskites (MHPs) have received significant interest for cost-effective, high-performance optoelectronic devices. In addition to the great successes in photovoltaics, their excellent l...Solution-processed metal halide perovskites (MHPs) have received significant interest for cost-effective, high-performance optoelectronic devices. In addition to the great successes in photovoltaics, their excellent luminescence and charge transport properties also make them promising for light emitting diodes (LEDs). To achieve high-efficiency perovskite LEDs (PeLEDs), extensive efforts have been carried out to enhance radiative recombination rates by confining the electrons and holes. In addition to enhancing radiative recombination rates, it is equally important to decrease the non-radiative recombination for improving the device performance. Passivation of the defects could be an efficient way for reducing the non-radiative recombination.展开更多
In this work,cubic-phased CeO_(2):18 mol%Yb^(3+)/2 moI%Er^(3+)nanospheres were prepared by coprecipitation method,in which the size of nanosphere was precisely controlled by regulating the amount of coprecipitator ure...In this work,cubic-phased CeO_(2):18 mol%Yb^(3+)/2 moI%Er^(3+)nanospheres were prepared by coprecipitation method,in which the size of nanosphere was precisely controlled by regulating the amount of coprecipitator urea.The morphology evolution of CeO_(2):18%Yb3+/2%Er^(3+)samples that vary from nanosphere to nano-flower with extending the reaction time was elaborately investigated via increasing the amount of urea and increasing the reaction temperature.The influence of non-radiative relaxation(NR)processes and surface quenching on up-conversion emission output of CeO_(2):18%Yb^(3+)/2%Er^(3+)was investigated through varying the sizes and environmental temperatures.Tissue imaging experiment demonstrates that CeO_(2):18%Yb^(3+)/2%Er^(3+)nanospheres have the potential to act as luminescent imaging reagents in tissue imaging.展开更多
The fabrication of multifunctional electronic devices based on the intriguing natures of organic semiconductors is crucial for organic electronics.Ultranarrow-bandgap materials are in urgent demand for fabricating hig...The fabrication of multifunctional electronic devices based on the intriguing natures of organic semiconductors is crucial for organic electronics.Ultranarrow-bandgap materials are in urgent demand for fabricating high-performance organic photovoltaic(OPV)cells and highly sensitive near-infrared organic photodetectors(OPDs).By combining alkoxy modification and an asymmetric strategy,three narrowbandgap electronic acceptors(BTP-4F,DO-4F,and QO-4F)were synthesized with finely tuned molecular electrostatic potential(ESP)distributions.Through the careful modulation of electronic configurations,the optical absorption onsets of DO-4F and QO-4F exceeded 1μm.The experimental and theoretical results suggest that the small ESP of QO-4F is beneficial for achieving a low nonradiative voltage loss,while the large ESP of BTP-4F can help obtain high exciton dissociation efficiency.By contrast,the asymmetric acceptor DO-4F with a moderate ESP possesses balanced voltage loss and exciton dissociation,yielding the best power conversion efficiency of 13.6%in the OPV cells.OPDs were also fabricated based on the combination of PBDB-T:DO-4F,and the as-fabricated device outputs a high shot-noise-limited specific detectivity of 3.05×10^(13) Jones at 850 nm,which is a very good result for near-infrared OPDs.This work is anticipated to provide a rational way of designing high-performance ultranarrow-bandgap organic semiconductors by modulating the molecular ESP.展开更多
Interfacial imperfections between the perovskite layer and the electron transport layer(ETL)in perovskite solar cells(PSCs)can lead to performance loss and negatively influence long-term operational stability.Here,we ...Interfacial imperfections between the perovskite layer and the electron transport layer(ETL)in perovskite solar cells(PSCs)can lead to performance loss and negatively influence long-term operational stability.Here,we introduce an interface engineering method to modify the interface between perovskite and ETL by using multifunctional carbon dots(CDs).C=O in the CDs can chelate with the uncoordinated Pb2+in the perovskite material,inhibit interfacial recombination,and enhance the performance and stability of device.In addition,–OH in CDs forms hydrogen bonds with I-and organic cation in perovskite,inhibiting light-induced I2release and organic cation volatilization,causing irreversible degradation of perovskite films,thereby enhancing the long-term operational stability of PSCs.Consequently,we achieve the champion inverted device with an efficiency of 24.02%.The CDs-treated PSCs exhibit high operational stability,and the maximum power point tracking only attenuates by 12.5%after 1000 h.Interfacial modification engineering supported by multifunctional quantum dots can accelerate the road to stable PSCs.展开更多
P-i-n type perovskite solar cells(PSCs)manifest some promising advantages in terms of remarkable operational stability,low-temperature processability,and compatibility for multi-junction devices,whereas they have rela...P-i-n type perovskite solar cells(PSCs)manifest some promising advantages in terms of remarkable operational stability,low-temperature processability,and compatibility for multi-junction devices,whereas they have relatively low efficiency compared to n-i-p type PSCs because of mismatched energy level alignment and poor interface quality at both n-and p-type contacts.Recently,great progress has been achieved in the p-i-n type PSCs,and efficiencies exceeding 25%have been reported from different research groups.Herein,state-of-the-art strategies in the deployment of high-performance p-i-n type PSCs have been systematically reviewed including engineering top-surface and buried interface of perovskitefilms with eliminated non-radiative charge recombination,modulating conduction types of the perovskites with well aligned energy level to facilitate charge transport,and designing effective hole transport materials for lossless charge extraction,and so on,based on which perspectives in the further design of efficient,stable and scalable p-i-n type PSCs are provided from the aspects of materials design,device fabrication,scalability and functionalization.展开更多
Tellurite glasses with the composition of xTm2O3-(6-x)Y2O3-3Na2O-25ZnO-66TeO2(where 0≤x≤6)were obtained by the melt-quenching technique.Absorption(300 K),excitation(300 K)and fluorescence spectra(300 K)as well as fl...Tellurite glasses with the composition of xTm2O3-(6-x)Y2O3-3Na2O-25ZnO-66TeO2(where 0≤x≤6)were obtained by the melt-quenching technique.Absorption(300 K),excitation(300 K)and fluorescence spectra(300 K)as well as fluorescence decay curves of Tm^3+-doped title glasses are presented and discussed in details.The Judd-Ofelt analysis based on the room temperature absorption spectrum was applied for determination of fundamental fluorescence properties such as radiative transition probabilities(AT),branching ratios(βR),radiative lifetimes(τR)of the emitting levels of the Tm^3+ion and stimulated emission cross-sections(σem).Fluorescence spectra were recorded and analysed in the visible and near-infrared spectral range.The emission and effective cross-section were calculated for the 3F4→3H6 transition,showing that the investigated glasses are promising laser host materials,operating at 1.8μm.The observed concentration quenching and non-exponential decay curves from the 1 G4 and 3H4 states indicate nonradiative energy transfer between Tm^3+ions.The analysis of non-exponential fluorescence decay curves from the 1 G4 and 3H4 levels was carried out in framework of the InokutiHirayama and Yokota-Tanimoto models and energy transfer microparameters were determined.The self-quenching model was proposed for describing relaxation of the first excited state of the Tm^3+ion.展开更多
We study sufficient conditions on radial and non-radial weight functions on the upper half-plane that guarantee norm approximation of functions in weighted Bergman,weighted Dirichlet,and weighted Besov spaces on the u...We study sufficient conditions on radial and non-radial weight functions on the upper half-plane that guarantee norm approximation of functions in weighted Bergman,weighted Dirichlet,and weighted Besov spaces on the upper half-plane by dilatations and eventually by analytic polynomials.展开更多
Methods of finding quasi-normal modes of non-rotating relativistic stars have been well established, however, none of the existing treatments which take spacetime and fluid oscillations fully into account can determin...Methods of finding quasi-normal modes of non-rotating relativistic stars have been well established, however, none of the existing treatments which take spacetime and fluid oscillations fully into account can determine modes of long decay time, e.g., the p and g mode series, or the f modes for stars with low compactness ratio （M/R）. In this paper we show how the quasi-normal modes of long lifetime can be determined through refinements of a treatment originally due to Detweiler and Lindblom. The determination of the p mode series has been argued in the literature to have implication on the life time of gravitational wave sources and stellar stability. In this paper we 1） provide detailed steps in our treatment to facilitate future effort in this direction; 2） correct mistakes in the literature on the formulation; and 3） analyse the accuracy of the quasi-normal mode frequencies obtained and the limitations of the treatment.展开更多
文摘Radiation protection programs aims to reduce the radiation dose to the lowest possible level under the Dose Limit (DL) limit by the national or international laws, while the dose monitoring programs working as scale used to evaluating the efficiency of these programs and tools. In this study, the average of the annual Eff dose for the intensive care units at Hamad General Hospital (HGH) is less than the 50% of DL. It was aiming also to evaluate the efficiency of the radiation safety requirements (especially the shielding Adequacy) for the non radiation workers at oncology centers, hence several monitors were installed in chosen locations outside the radiation treatment machine from 2007 to 2011.
文摘In this thesis,we consider the existence of solutions for the following mixed dispersion nonlinear Schrödinger equation■where is a continuous function,,.We shall prove that(1)has multiple non-radial solutions by variational method.This paper provides a method to prove compactness for the study of the mixed dispersion nonlinear Schrödinger equation with quasilinear terms.
基金financially supported by the National Natural Science Foundation of China(51873177,52303252)the Natural Science Foundation of Hunan Province(2024JJ4039)+1 种基金the Advanced Photoelectricity and Supramolecular Functional Materials of the Ministry of Education(IRT-17R90)the Hunan 2011 Collaborative Innovation Centre of Chemical Engineering&Technology with Environmental Benignity and Effective Resource Utilization。
文摘Ternary blending as one of the most successful strategies has achieved continuous performance breakthroughs in organic solar cells(OSCs)over the past few years.Here,a small molecule featuring a dithieno[3,2-f:2′,3′-h]phthalimide derivative as the intermediate unit,named DTP-C8-R,is designed and utilized as the third component to construct ternary OSCs(TOSCs).The increased molecular packing of L8-BO as well as the charge transfer excitons between PM6 and DTP-C8-R lead to a very low nonradiative energy loss of 0.179 eV and a high open-circuit voltage(V_(OC))of 0.910 V in the TOSCs based on the PM6:L8-BO host blend.Moreover,the DTP-C8-R:PM6:L8-BO film(0.05:0.95:1.2,w/w)possesses better fibrous nanophase separation and the enhancedπ-πstacking ordering of the acceptors with a larger crystal coherence length compared with the PM6:L8-BO blend film,so the TOSCs present more efficient exciton dissociation,longer carrier lifetime,faster carrier transport and less charge recombination.It boosts the power conversion efficiency to 19.22%with a short-circuit current density of 27.10 mA cm^(-2).This work demonstrates that the small molecule based on a dithieno[3,2-f:2′,3′-h]phthalimide derivative as the minor component is an executable strategy to achieve high-performance TOSCs with high V_(OC).
基金supports from the National Natural Science Foundation of China(11904302,61921005)Major Project of the Science and Technology in Fujian Province of China(2019HZ020013)Major Science and Technology Projects in Xiamen of China(3502Z20191015).
文摘With regard to micro-light-emitting diodes(micro-LEDs),their excellent brightness,low energy consumption,and ultrahigh resolution are significant advantages.However,the large size of traditional inorganic phosphors and the number of side defects have restricted the practical applications of small sized micro-LEDs.Recently,quantum dot(QD)and nonradiative energy transfer(NRET)have been proposed to solve existing problems.QDs possess nanoscale dimensions and high luminous efficiency,and they are suitable for NRET because they are able to nearly contact the micro-LED chip.The NRET between QDs and micro-LED chip further improves the color conversion efficiency(CCE)and effective quantum yield(EQY)of full-color micro-LED devices.In this review,we discuss the NRET mechanism for QD micro-LED devices,and then nano-pillar LED,nano-hole LED,and nano-ring LED are introduced in detail.These structures are beneficial to the NRET between QD and micro-LED,especially nano-ring LED.Finally,the challenges and future envisions have also been described.
基金supported by the National Natural Science Foundation of China(U21A20331,81903743,22005322,22279151,and 22275004)National Science Fund for Distinguished Young Scholars(21925506).
文摘This study presents experimental evidence of the dependence of non-radiative recombination processes on the electron-phonon coupling of perovskite in perovskite solar cells(PSCs).Via A-site cation engineering,a weaker electron-phonon coupling in perovskite has been achieved by introducing the structurally soft cyclohexane methylamine(CMA^(+))cation,which could serve as a damper to alleviate the mechanical stress caused by lattice oscillations,compared to the rigid phenethyl methylamine(PEA^(+))analog.It demonstrates a significantly lower non-radiative recombination rate,even though the two types of bulky cations have similar chemical passivation effects on perovskite,which might be explained by the suppressed carrier capture process and improved lattice geometry relaxation.The resulting PSCs achieve an exceptional power conversion efficiency(PCE)of 25.5%with a record-high opencircuit voltage(V_(OC))of 1.20 V for narrow bandgap perovskite(FAPbI_(3)).The established correlations between electron-phonon coupling and non-radiative decay provide design and screening criteria for more effective passivators for highly efficient PSCs approaching the Shockley-Queisser limit.
文摘Analytical expressions are given for computing the magnetic potential and charac-teristic functions produced by the non-radial deflectors.These expressions are useful for designingthe defiectors such as those used in the color picture tubes and the electron beam lithographysystem.The computing results are in agreement with the measured values.
基金support by the National Key R&D Program of China(Nos.2020YFA0714603 and 2020YFA0714604)。
文摘The heavy-atom effect of halogen(Br and I)has been widely employed for boosting spin-crossover in organic molecules,while recent investigation indicated halogen-substitution can also enhance fluorescence and even lead to aggregation-induced emission(AIE).In this work,we investigated ultrafast excited state dynamics of a halogen-substituted model system,i.e.squaryliums NSQ-R(R=H,Cl,Br,I),by using femtosecond spectroscopy and theoretical approach.Fast external reorganization(Ex-re,~3 ps)and slow internal reorganization(In-re,5-20 ps)were observed,while quantitative fitting indicated halogen-substitution leads to a slower non-radiative S1→S0 decay(k_(NR)^(s))and subsequently enhanced fluorescence emitting.By analyzing the extracted k_(NR)^(s)within theoretical framework of non-radiative transition in the strong coupling regime,a plausible AIE mechanism of NSQs was revealed.Our work provides a clear picture on non-radiative dynamics of halogen-substituted squaryliums,which might be useful for future development of organic dyes.
基金supported by the National Natural Science Foundation of China(51802081,62074052,and 62104061)the Natural Science Foundation of Henan Province(232300420145).
文摘The presence of SnZn-related defects in Cu_(2)ZnSn(S,Se)_(4)(CZTSSe)absorber results in large irreversible energy loss and extra irreversible electron-hole non-radiative recombination,thus hindering the efficiency enhancement of CZTSSe devices.Although the incorporation of Ag in CZTSSe can effectively suppress the SnZn-related defects and significantly improve the resulting cell performance,an excellent efficiency has not been achieved to date primarily owing to the poor electrical-conductivity and the low carrier density of the CZTSSe film induced by Ag substitution.Herein,this study exquisitely devises an Ag/H co-doping strategy in CZTSSe absorber via Ag substitution programs followed by hydrogen-plasma treatment procedure to suppress SnZn defects for achieving efficient CZTSSe devices.In-depth investigation results demonstrate that the incorporation of H in Ag-based CZTSSe absorber is expected to improve the poor electrical-conductivity and the low carrier density caused by Ag substitution.Importantly,the C=O and O-H functional groups induced by hydrogen incorporation,serving as an electron donor,can interact with under-coordinated cations in CZTSSe material,effectively passivating the SnZn-related defects.Consequently,the incorporation of an appropriate amount of Ag/H in CZTSSe mitigates carrier non-radiative recombination,prolongs minority carrier lifetime,and thus yields a champion efficiency of 14.74%,showing its promising application in kesterite-based CZTSSe devices.
基金the financial support from The National Basic Research Program of China(No.2014CB643802)Ministry of Science and Technology(No.2016YFB0401001)the State Key Laboratory of Advanced Technologies for Comprehensive Utilization of Platinum Metals
文摘Room-temperature phosphorescence（RTP） materials have attracted great attention due to their involvement of excited triplet states and comparatively long decay lifetimes.In this short review,recent progress on enhancement of RTP from purely organic materials is summarized.According to the mechanism of phosphorescence emission,two principles are discussed to construct efficient RTP materials：one is promoting intersystem crossing（ISC） efficiency by using aromatic carbonyl,heavyatom,or/and heterocycle/heteroatom containing compounds;the other is suppressing intramolecular motion and intermolecular collision which can quench excited triplet states,including embedding phosphors into polymers and packing them tightly in crystals.With aforementioned strategies,RTP from purely organic materials was achieved both in fluid and rigid media.
基金financially supported by the National Natural Science Foundation of China (No. 21734007)Tianjin government
文摘Room temperature phosphorescence(RTP) has drawn increasing attention for its great potential in practical applications.Polymers with large molecular weights and long chains tend to form coil, which can endow them with a high degree of possible rigidity and result in the much restricted non-radiative transition. Also, the intertwined structure of polymers could isolate the oxygen and humidity effectively, thus reducing the consumption of triplet excitons. In consideration of these points, organic polymers would be another kind of ideal platform to realize RTP effect. This short review summarized the design strategy of the purely organic room temperature phosphorescence polymers, mainly focusing on the building forms of polymers and the corresponding inherent mechanisms,and also gives some outlooks on the further exploration of this field at the end of this paper.
基金supported by the National Natural Science Foundation of China(62074037,52002073)the Science and Technology Department of Fujian Province(2020I0006)+3 种基金the Natural Science Foundation of Fujian Province(2019J01218)the Fujian Science&Technology Innovation Laboratory for Optoelectronic Information of China(2021ZZ124)the Education and Scientific Research Project of Fujian Province(JAT200372)the Scientific Research Project of Fujian Jiangxia University(JXZ2019006)。
文摘The passivation of non-radiative states and inhibition of band tailings are desirable for improving the open-circuit voltage(V_(oc))of CZTSSe thin-film solar cells.Recently,alkali metal doping has been investigated to passivate defects in CZTSSe films.Herein,we investigate Li doping effects by applying Li OH into CZTSSe precursor solutions,and verify that carrier transport is enhanced in the CZTSSe solar cells.Systematic characterizations demonstrate that Li doping can effectively passivate non-radiative recombination centers and reduce band tailings of the CZTSSe films,leading to the decrease in total defect density and the increase in separation distance between donor and acceptor.Fewer free carriers are trapped in the band tail states,which speeds up carrier transport and reduces the probability of deep-level defects capturing carriers.The charge recombination lifetime is about twice as long as that of the undoped CZTSSe device,implying the heterojunction interface recombination is also inhibited.Besides,Li doping can increase carrier concentration and enhance build-in voltage,leading to a better carrier collection.By adjusting the Li/(Li+Cu)ratio to 18%,the solar cell efficiency is increased significantly to 9.68%with the fill factor(FF)of 65.94%,which is the highest FF reported so far for the flexible CZTSSe solar cells.The increased efficiency is mainly attributed to the reduction of V_(oc)deficit and the improved CZTSSe/Cd S junction quality.These results open up a simple route to passivate non-radiative states and reduce the band tailings of the CZTSSe films and improve the efficiency of the flexible CZTSSe solar cells.
文摘Solution-processed metal halide perovskites (MHPs) have received significant interest for cost-effective, high-performance optoelectronic devices. In addition to the great successes in photovoltaics, their excellent luminescence and charge transport properties also make them promising for light emitting diodes (LEDs). To achieve high-efficiency perovskite LEDs (PeLEDs), extensive efforts have been carried out to enhance radiative recombination rates by confining the electrons and holes. In addition to enhancing radiative recombination rates, it is equally important to decrease the non-radiative recombination for improving the device performance. Passivation of the defects could be an efficient way for reducing the non-radiative recombination.
基金Natural Science Foundation of Shaanxi Provincial Department of Education(20JK0486)Natural Science Foundation of Shaanxi Province(2021JQ-799)Graduate Innovation Research Project of Baoji University of Arts and Sciences(YJSCX22YB14)。
文摘In this work,cubic-phased CeO_(2):18 mol%Yb^(3+)/2 moI%Er^(3+)nanospheres were prepared by coprecipitation method,in which the size of nanosphere was precisely controlled by regulating the amount of coprecipitator urea.The morphology evolution of CeO_(2):18%Yb3+/2%Er^(3+)samples that vary from nanosphere to nano-flower with extending the reaction time was elaborately investigated via increasing the amount of urea and increasing the reaction temperature.The influence of non-radiative relaxation(NR)processes and surface quenching on up-conversion emission output of CeO_(2):18%Yb^(3+)/2%Er^(3+)was investigated through varying the sizes and environmental temperatures.Tissue imaging experiment demonstrates that CeO_(2):18%Yb^(3+)/2%Er^(3+)nanospheres have the potential to act as luminescent imaging reagents in tissue imaging.
基金the support from the National Natural Science Foundation of China(NSFC,21835006)the financial support from the NSFC(22075301 and 22122905)+2 种基金the Youth Innovation Promotion Association CAS(2018043)the Key Research Program of the Chinese Academy of Sciences,Grant NO.XDPB13-3supported by the Beijing National Laboratory for Molecular Sciences(BNLMS-CXXM-201903)。
文摘The fabrication of multifunctional electronic devices based on the intriguing natures of organic semiconductors is crucial for organic electronics.Ultranarrow-bandgap materials are in urgent demand for fabricating high-performance organic photovoltaic(OPV)cells and highly sensitive near-infrared organic photodetectors(OPDs).By combining alkoxy modification and an asymmetric strategy,three narrowbandgap electronic acceptors(BTP-4F,DO-4F,and QO-4F)were synthesized with finely tuned molecular electrostatic potential(ESP)distributions.Through the careful modulation of electronic configurations,the optical absorption onsets of DO-4F and QO-4F exceeded 1μm.The experimental and theoretical results suggest that the small ESP of QO-4F is beneficial for achieving a low nonradiative voltage loss,while the large ESP of BTP-4F can help obtain high exciton dissociation efficiency.By contrast,the asymmetric acceptor DO-4F with a moderate ESP possesses balanced voltage loss and exciton dissociation,yielding the best power conversion efficiency of 13.6%in the OPV cells.OPDs were also fabricated based on the combination of PBDB-T:DO-4F,and the as-fabricated device outputs a high shot-noise-limited specific detectivity of 3.05×10^(13) Jones at 850 nm,which is a very good result for near-infrared OPDs.This work is anticipated to provide a rational way of designing high-performance ultranarrow-bandgap organic semiconductors by modulating the molecular ESP.
基金supported by the National Natural Science Foundation of China(52172237,22261142666)the Shaanxi International Cooperation Project(2020KWZ-018)+3 种基金the Shaanxi Science Fund for Distinguished Young Scholars(2022JC-21)the Research Fund of the State Key Laboratory of Solidification Processing(NPU),China(2021-QZ-02)the Fundamental Research Funds for the Central Universities(D5000220033)the Hong Kong Scholars Program(XJ2022025)。
文摘Interfacial imperfections between the perovskite layer and the electron transport layer(ETL)in perovskite solar cells(PSCs)can lead to performance loss and negatively influence long-term operational stability.Here,we introduce an interface engineering method to modify the interface between perovskite and ETL by using multifunctional carbon dots(CDs).C=O in the CDs can chelate with the uncoordinated Pb2+in the perovskite material,inhibit interfacial recombination,and enhance the performance and stability of device.In addition,–OH in CDs forms hydrogen bonds with I-and organic cation in perovskite,inhibiting light-induced I2release and organic cation volatilization,causing irreversible degradation of perovskite films,thereby enhancing the long-term operational stability of PSCs.Consequently,we achieve the champion inverted device with an efficiency of 24.02%.The CDs-treated PSCs exhibit high operational stability,and the maximum power point tracking only attenuates by 12.5%after 1000 h.Interfacial modification engineering supported by multifunctional quantum dots can accelerate the road to stable PSCs.
基金supported by the National Research Foundation of Korea(NRF)grants funded by the Korean government(MSIT)under contract NRF-2021R1A3B1076723(Research Leader Program)and NRF2022M3J1A1085280(Carbon Neutral Technology Program)supported by the Korea Evaluation Institute of Industrial Technology under contract 20016588.
文摘P-i-n type perovskite solar cells(PSCs)manifest some promising advantages in terms of remarkable operational stability,low-temperature processability,and compatibility for multi-junction devices,whereas they have relatively low efficiency compared to n-i-p type PSCs because of mismatched energy level alignment and poor interface quality at both n-and p-type contacts.Recently,great progress has been achieved in the p-i-n type PSCs,and efficiencies exceeding 25%have been reported from different research groups.Herein,state-of-the-art strategies in the deployment of high-performance p-i-n type PSCs have been systematically reviewed including engineering top-surface and buried interface of perovskitefilms with eliminated non-radiative charge recombination,modulating conduction types of the perovskites with well aligned energy level to facilitate charge transport,and designing effective hole transport materials for lossless charge extraction,and so on,based on which perspectives in the further design of efficient,stable and scalable p-i-n type PSCs are provided from the aspects of materials design,device fabrication,scalability and functionalization.
文摘Tellurite glasses with the composition of xTm2O3-(6-x)Y2O3-3Na2O-25ZnO-66TeO2(where 0≤x≤6)were obtained by the melt-quenching technique.Absorption(300 K),excitation(300 K)and fluorescence spectra(300 K)as well as fluorescence decay curves of Tm^3+-doped title glasses are presented and discussed in details.The Judd-Ofelt analysis based on the room temperature absorption spectrum was applied for determination of fundamental fluorescence properties such as radiative transition probabilities(AT),branching ratios(βR),radiative lifetimes(τR)of the emitting levels of the Tm^3+ion and stimulated emission cross-sections(σem).Fluorescence spectra were recorded and analysed in the visible and near-infrared spectral range.The emission and effective cross-section were calculated for the 3F4→3H6 transition,showing that the investigated glasses are promising laser host materials,operating at 1.8μm.The observed concentration quenching and non-exponential decay curves from the 1 G4 and 3H4 states indicate nonradiative energy transfer between Tm^3+ions.The analysis of non-exponential fluorescence decay curves from the 1 G4 and 3H4 levels was carried out in framework of the InokutiHirayama and Yokota-Tanimoto models and energy transfer microparameters were determined.The self-quenching model was proposed for describing relaxation of the first excited state of the Tm^3+ion.
文摘We study sufficient conditions on radial and non-radial weight functions on the upper half-plane that guarantee norm approximation of functions in weighted Bergman,weighted Dirichlet,and weighted Besov spaces on the upper half-plane by dilatations and eventually by analytic polynomials.
基金supported by the Science Foundation of the Education Department of Hunan Province of China (Grant No. 07c578)in part by the US National Science Foundation NRACthe McDonnell Center for the Space Sciences of the Washington University(Grant No. MCA93S025)
文摘Methods of finding quasi-normal modes of non-rotating relativistic stars have been well established, however, none of the existing treatments which take spacetime and fluid oscillations fully into account can determine modes of long decay time, e.g., the p and g mode series, or the f modes for stars with low compactness ratio （M/R）. In this paper we show how the quasi-normal modes of long lifetime can be determined through refinements of a treatment originally due to Detweiler and Lindblom. The determination of the p mode series has been argued in the literature to have implication on the life time of gravitational wave sources and stellar stability. In this paper we 1） provide detailed steps in our treatment to facilitate future effort in this direction; 2） correct mistakes in the literature on the formulation; and 3） analyse the accuracy of the quasi-normal mode frequencies obtained and the limitations of the treatment.
