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Trap-Mediated Two-Step Sensitization of Manganese Dopants in Perovskite Nanocrystals
摘要： Halide perovskite nanocrystals hold promise for printable optoelectronic and photonic applications. Doping enhances their functionalities and is being investigated for substituting lead with environmentally friendlier elements. The most investigated dopant is Mn2+ that acts as a color center sensitized by the host excitons. The sensitization mechanism is far from understood and no comprehensive picture of the energy-transfer process has been proposed. Similarly, the role of shallow states - particularly abundant in defect tolerant materials - is still unknown. Here, we address this problem via spectroscopic studies at controlled excitation density and temperature on Mn:CsPbCl3 nanocrystals. Our results indicate a two-step process involving exciton localization in a shallow metastable state that mediates the thermally-assisted sensitization of the Mn2+-emission, which is completely quenched for T<200K. At T≤60K, however, such emission surprisingly reappears, suggesting direct energy-transfer from band-edge states. Electron spin resonance supports this picture revealing the signatures of conformational rearrangements below 70K, possibly removing the potential barrier for sensitization. Our results demystify anomalous behaviors of the exciton-to-Mn2+ energy-transfer mechanism and highlight the role of shallow defects in the photophysics of doped perovskite nanostructures.
关键词： Halide perovskite nanocrystals,energy-transfer,spectroscopic studies,Mn2+ dopants,shallow states
更新于2025-09-09 09:28:46
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Structural and photoluminescence properties of UV-excited Er3+ doped Ba2CaWO6 yellowish-green phosphors
摘要： Double perovskite Ba2CaWO6 phosphors doped with different concentrations of Er3+ have been synthesized by the conventional solid state reaction method in air at 1250 °C and are characterized by X-ray diffraction analysis (XRD), Energy Dispersive X-ray Spectrometer (EDS), Scanning electron microscope (SEM), Transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FTIR) and Photoluminescence measurements. An intense green and weak red emissions are observed at 566 nm (4S3/2 →4I15/2), 680 nm (4F9/2 →4I15/2) under 314 nm, 378 nm corresponding to charge transfer band and rare earth excitations respectively. Under charge transfer excitation Ba2CaWO6:xEr3+ samples exhibit high intense emission peaks of Er3+ than the rare earth excitation. This is due to an efficient energy transfer from WO6 6- to Er3+. The maximum emission intensity was observed for 0.08 wt% concentration of Er3+ ions in Ba2CaWO6 phosphors. The critical energy transfer distance among Er3+ ions is calculated to be 15.18 ? and the quenching mechanism is due to dipole-dipole interaction. The energy transfer mechanism is discussed based on the energy level diagram of Er3+. The radiative lifetimes were determined from the fluorescence decay analysis. The CIE color coordinates were calculated from the emission spectra. The result shows that Ba2CaWO6:Er3+ phosphor can be considered as a potential candidate for UV excited yellowish-green phosphor for display applications.
关键词： Ba2CaWO6,phosphor,photoluminescence,Er3+,yellowish-green emission,energy transfer
更新于2025-09-09 09:28:46
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Photophysics at Unusually High Dye Concentrations
摘要： The study of the interaction of light with systems at high dye concentrations implies a great challenge because several factors, such as emission reabsorption, dye aggregation, and energy trapping, hinder rationalization and interpretation of the involved photophysical processes. Space constraints induce dye interaction even in the absence of ground state stabilization of dimers and oligomers. At distances on the order of 1 nm, statistical energy traps are usually observed. At longer distances, excited state energy transfer takes place. Most of these factors do not result in ground state spectroscopic changes. Rather, fluorescence phenomena such as inner filter effects, concentration-dependent Stokes’ shifts, and changes in quantum yields and decay times are evidenced. Photophysical studies are commonly carried out at high dilution, to minimize dye?dye interactions and emission reabsorption, and in the absence of light scattering. Under these conditions, the system becomes rather simple. Fluorescence and triplet quantum yields become molecular properties and can be easily related to ratios of rate constants. However, many systems containing dyes able to fulfill specific functions, whether man-made or biological, are far from being dilute and scattering-free. The photosynthetic apparatus is a paradigmatic example. It is clear that isolation of components allows gathering relevant information about complex systems. However, knowledge of the photophysical behavior in the unaltered environment is essential in most cases. Complexity generally increases when light scattering is present. Despite that, our experience shows that light scattering, when correctly handled, may even simplify the task of unraveling molecular parameters. We show that methods and models aiming at the determination and interpretation of fluorescence and triplet quantum yields as well as energy transfer efficiencies can be developed on the basis of simple light-scattering theories. Photophysical studies were extended to thin films and layer-by-layer assemblies. Procedures are presented for the evaluation of fluorescence reabsorption in concentrated fluid solutions up to the molar level, which are being applied to ionic liquids, in which the emitting species are the bulk ions. Fluorescence reabsorption models proved to be useful in the interpretation of the photophysics of living organisms such as plant leaves and fruits. These new tools allowed the assessment of chlorophyll fluorescence at the chloroplast, leaf and canopy levels, with implications in remote sensing and the development of nondestructive optical methods.
关键词： light scattering,dye concentrations,photophysics,fluorescence reabsorption,energy transfer
更新于2025-09-09 09:28:46
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Synthesis of Re(I) Rings Comprising Different Re(I) Units and Their Light-Harvesting Abilities
摘要： Trimethylamine N-oxide (Me3NO) could selectively remove only one CO ligand from fac-[Re(N^N)(CO)3(PR2R′)]+ (N^N = diimine ligand), whereby only the CO ligand in the trans position to the phosphorus ligand was selectively removed to give cis,trans-[ReI(N^N)(CO)2(PR2R′)(L)]n+ in good yields. This decarbonylation reaction using Me3NO was found to be especially useful for synthesizing biscarbonyl Re(I) complexes with electron-withdrawing groups in the diimine ligand, which could not be synthesized or were obtained only in low yields by the photochemical method. Me3NO also selectively removed the carbonyl ligands in the trans position to the phosphorus ligands from the edge Re(I) complex units, which have the fac-[Re(N^N)(CO)3(PR2R′)]+ structure, in linear-shaped Re(I) multinuclear complexes. This reaction was successfully applied to synthesize a novel precursor with ring-shaped multinuclear Re complexes (Re-rings) comprising different kinds of Re(I) units. The newly synthesized Re-rings, which consist of one Re unit with a 4,4′-bis(trifluoromethyl)-2,2′-bipyridine (CF3bpy) ligand and one or two Re unit(s) with a 2,2′-bipyridine (bpy) ligand, showed almost quantitative excitation-energy harvesting ability from the Re unit(s) with bpy to that with CF3bpy.
关键词： multinuclear complexes,decarbonylation reaction,excitation-energy transfer,light-harvesting abilities,Re(I) rings
更新于2025-09-09 09:28:46
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Estimating the Individual Spectroscopic Properties of Three Unique Eu <sup>III</sup> Sites in a Coordination Polymer
摘要： We isolated a coordination polymer with the formula [Eu3(3,5-dcba)9(H2O)(dmf)3]·2dmf, with three unique EuIII coordination sites in the asymmetric unit, with the EuIII ions bridged by 3,5-dichlorobenzoato (3,5-dcba) ligands. The coordination polymer crystallized in the triclinic space group P1? with unit cell dimensions a = 12.4899(15), b = 16.326(2), and c = 25.059(3) ?, α = 84.271(3)°, β = 84.832(3)°, and γ = 68.585(3)° and V = 4725.2(10) ?3. The characteristic 5D0 → 7FJ (J = 0?4) EuIII transitions were observed upon ligand-centered excitation. Emission lifetimes of 0.825 ± 0.085 and 1.586 ± 0.057 ms were observed and were attributed to the sites with coordination of water or dimethylformamide (dmf) molecules to each ion, respectively. Through a combination of spectroscopy and calculations, we determined the photophysical properties of each unique EuIII site. Energy-transfer rates ligand → EuIII were determined for each unique site using the overlapped polyhedra method. The rates depend on the coordinated water molecules and the different donor?acceptor distances. The two sites without coordinated water molecules and shortest donor?acceptor distance display the fastest energy-transfer rate ligand → EuIII, whereas the site with coordinated water molecules and longest donor?acceptor distance displays the slowest energy-transfer rate. Donor?acceptor distances were estimated computationally and were confirmed by calculating the frontier orbitals in the asymmetric units of the polymer using density functional theory.
关键词： coordination polymer,photophysical properties,energy-transfer rates,density functional theory,EuIII
更新于2025-09-09 09:28:46
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A stoichiometric terbium-europium dyad molecular thermometer: energy transfer properties
摘要： The optical thermometer has shown great promise for use in the fields of aeronautical engineering, environmental monitoring and medical diagnosis. Self-referencing lanthanide thermo-probes distinguish themselves because of their accuracy, calibration, photostability, and temporal dimension of signal. However, the use of conventional lanthanide-doped materials is limited by their poor reproducibility, random distance between energy transfer pairs and interference by energy migration, thereby restricting their utility. Herein, a strategy for synthesizing hetero-dinuclear complexes that comprise chemically similar lanthanides is introduced in which a pair of thermosensitive dinuclear complexes, cycTb-phEu and cycEu-phTb, were synthesized. Their structures were geometrically optimized with an internuclear distance of approximately 10.6 ?. The sensitive linear temperature-dependent luminescent intensity ratios of europium and terbium emission over a wide temperature range (50–298 K and 10–200 K, respectively) and their temporal dimension responses indicate that both dinuclear complexes can act as excellent self-referencing thermometers. The energy transfer from Tb3+ to Eu3+ is thermally activated, with the most important pathway involving the 7F1 Eu3+ J-multiplet at room temperature. The energy transfer from the antenna to Eu3+ was simulated, and it was found that the most important ligand contributions to the rate come from transfers to the Eu3+ upper states rather than direct ligand–metal transfer to 5D1 or 5D0. As the first molecular-based thermometer with clear validation of the metal ratio and a fixed distance between the metal pairs, these dinuclear complexes can be used as new materials for temperature sensing and can provide a new platform for understanding the energy transfer between lanthanide ions.
关键词： temperature sensing,hetero-dinuclear complexes,lanthanide,energy transfer,optical thermometer
更新于2025-09-09 09:28:46
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Ratiometric Fluorescence Sensing of Cu(II): Elucidation of FRET Mechanism and Bio‐Imaging Application
摘要： Rhodamine-formylaniline conjugate RFA has been developed as a Cu2+-selective ratiometric fluorescent probe. The probe shows high selectivity towards Cu2+ ion through both its absorption and emission properties; and has been characterized by 1H NMR, FTIR, ESI-MS spectroscopy. Sensing of Cu2+ proceed through FRET process which is nicely depicted from steady-state and fluorescence lifetime studies. From the measurement of fluorescence lifetime, the FRET mechanism has been established undoubtedly. The important parameters regarding FRET, namely the energy transfer efficiency (ΦEt) and the F?rster distance (R0) have also been calculated by fluorescence measurement. The origin of different emission bands has been distinguished by recording excitation spectra. The lowest detection limit (DL) for Cu2+ ion was 4.2 × 10?7 M in Tris-HCl buffered MeCN: H2O (10 mM, 1:1 v/v).
关键词： Time-resolved experiment,Confocal Bioimaging,Energy Transfer Efficiency,FRET,Fluorescent probes
更新于2025-09-09 09:28:46
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Quenching of Luminol Fluorescence at Nano-Bio Interface: Towards the Development of an Efficient Energy Transfer System
摘要： Surface modified colloidal gold (Au) and silver (Ag) nanoparticles (NPs) were used as efficient quenchers of luminol (LH2) fluorescence either in homogeneous aqueous medium or its noncovalent assembly with bovine serum albumin (BSA). The mechanism as well as the extent of fluorescence quenching was found to be strongly dependent on the nature of the nanoparticles. While simple static type fluorescence quenching mechanism was perceived with AuNP, a more complex protocol involving quenching sphere model was envisaged for AgNP quenching. Nevertheless, the magnitude of Stern-Volmer (SV) quenching constant (KSV ~ 108–1010 M?1) was calculated to be ca. 104 times more for surface quoted NPs in comparison with BSA–NP bioconjugates system. On the other hand, a highly efficient (E ≈ 95%) energy transfer (ET) process was predicted for LH2 captured in the hydrophobic assembly with BSA in presence of AgNP as an acceptor. The ET efficiency is critically dependent on the concentration of BSA and nicely correlated with the extent of NP surface coverage. However, fluorescence quenching on AuNP surface is relatively less responsive towards protein concentration, primarily due to the difference in surface activity as well as the mode of interaction of the protein with NPs.
关键词： Bionanosensors,Bovine serum albumin,Luminol,Metal nanoparticles,Energy transfer,Fluorescence quenching
更新于2025-09-09 09:28:46
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Luminescence and energy transfer studies of Ce3+/Dy3+ doped fluorophosphate glasses
摘要： The fluorophosphate (PKABfNf:P2O5+K2O+Al2O3+BaF2+NaF2) glasses doped with single and co-doped (Ce and/or Dy) were prepared by conventional melt quenching technique and characterized their luminescence properties. The emission spectra of co-doped glass (PKABfNfCeDy) showed a broad blue band of Ce3+ ions combined with the sharp peaks of Dy3+ ions. Judd-Ofelt (JO) intensity parameters have been obtained from the optical absorption spectra of 1.0 mol % of Dy3+ (PKABfNfDy1.0) glass. JO theory has been used to find the radiative properties of PKABfNfDy1.0 glass by using Futchbauer-Ladenbergh formula. The (Ce3+/Dy3+) co-doped glass exhibit radiative energy transfer (ET) from Ce3+ to Dy3+ upon UV excitation and then intensity is increased with increase in Dy3+ ion concentration. The ET mechanism from Ce3+ to Dy3+ ion has been analyzed. The theoretical ET efficiency and quantum yield values were calculated from the emission spectrum of the Ce3+ and (Ce3+/Dy3+) co-doped glasses. These results suggest that the co-doped PKABfNfCeDy glasses are promising candidate for commercial white light applications.
关键词： W-LEDs,Dysprosium,Fluorophosphate glasses,Energy transfer,Judd-Ofelt analysis,Quantum yield,Cerium
更新于2025-09-09 09:28:46
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On the efficient Te4+→Yb3+ cooperative energy transfer mechanism in tellurite glasses: A potential material for luminescent solar concentrators
摘要： Te4+/Yb3+ co-doped 80%TeO2-20%Li2O glasses (amounts in mol%) were prepared by the conventional melt-quenching method in an ambient atmosphere, in order to investigate their optical characteristics for application in solar cells. An efficient near-infrared down-conversion mechanism was observed in these samples, involving the emission of two near infrared photons (at around 978 nm) after the absorption of one photon in the ultraviolet-blue region. This effect occurred by means of a process of cooperative energy transfer (CET) from Te4+ to Yb3+ ions. The CET efficiency (h CET) was calculated from radiative transitions (lifetime) and also by a new method, developed in this work, based on rate equations quantifying the non-radiative transitions (thermal effect) involved in the system. The two methods showed very good agreement, with h CET between 82-100% obtained for the sample prepared using a higher Yb3+ concentration (4 mol%). The results suggested that these tellurite materials could have potential applications in improving the efficiency of silicon-based solar cells.
关键词： Te4+ ions,Thermal lens effect,Tellurite glass,Yb3+ ions,Down-conversion,Cooperative energy transfer
更新于2025-09-09 09:28:46