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Bismuth doped lead-free two-dimensional tin based halide perovskite single crystals
摘要： Heterovalent-metal doping is an efficient tool to tune the optoelectronic properties of the famous halide perovskites. Previous studies have focused on the heterovalent-doping in three-dimensional (3D) halide perovskites. However, there is a lack of such doping in two-dimensional perovskites which possess unique optoelectronic properties and improved chemical stability as compared to 3D analogues. Here, we present successful doping of Bismuth into the lattice of lead-free, two-dimensional perovskite PEA2SnBr4 single crystals. Structural characterizations demonstrate that the doped crystals possess identical crystal structure and layered morphology with the pristine one. Intriguingly, we find the PL peak and spectral shape can be tailored by tuning the concentration of Bi dopants. Femtosecond transient absorption spectroscopy is performed to understand the underlying mechanism related to tunable PL behaviors, and a clear picture of the Bismuth-doping impact is provided.
关键词： Global analysis fit,Femtosecond transient absorption spectra,Self-trapped excitons,Photoluminescence,Heterovalent-metal doping
更新于2025-09-04 15:30:14
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Low‐dimensional hybrid perovskites containing an organic cation with an extended conjugated system: tuning the excitonic absorption features
摘要： Low-dimensional hybrid perovskites are receiving increased attention. One of the advantages of the low dimensional hybrids over their 3D counterparts is their greater structural flexibility towards the incorporation of bigger, more complex, organic cations. In this communication, we introduce a pyrene derivative as an organic cation containing an extended π-system for use in a variety of low dimensional hybrids. We show that materials with different excitonic absorption features can be obtained by tuning the iodide/lead ratio in the precursor solutions, using the same pyrene cation. In this way, hybrids with optical characteristics corresponding to 2D, 1D and 0D hybrid perovskites are obtained. The formation and thermal stability of the different hybrids is analysed and compared.
关键词： excitons,stability,organic-inorganic hybrid composites,low-dimensional,perovskite phases
更新于2025-09-04 15:30:14
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Isotopic effects on phonons and excitons in diamond studied by deep-ultraviolet continuous-wave photoluminescence spectroscopy
摘要： Photoluminescence (PL) spectroscopy is performed for natural-abundance (N.A.C) and isotopically purified (13C) synthetic diamond using a deep-ultraviolet continuous-wave laser. Because the excitation source creates low-density low-temperature excitons even under a moderate excitation power, the PL spectra show suppressed collisional and thermal broadening with a high signal-to-noise ratio. Our approach can accurately resolve the isotopic effects. The experimentally determined effects for phonons and excitons in diamond are ΔETA = ?2.5 meV, ΔETO = ?4.9 meV, ΔELO = ?5.7 meV, and ΔEex = 14.5 meV.
关键词： diamond,photoluminescence spectroscopy,isotopic effects,excitons,phonons
更新于2025-09-04 15:30:14
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Layered Hybrid Perovskites for Highly Efficient Three-Photon Absorbers: Theory and Experimental Observation
摘要： Multiphoton absorption may find many technological applications, such as enhancing the conversion efficiency of solar cells by the utilization of sub-band-energy photons, below-bandgap photodetection through the simultaneous absorption of several infrared photons for photocurrent generation, or light frequency upconversion for high-resolution, 3D imaging. To enhance multiphoton absorption in semiconducting materials, one of the strategies is to explore low-dimensional excitons. Here, a quantum perturbation theory on a giant enhancement in three-photon absorption (3PA) arising from 2D excitons in multilayered crystals of organic–inorganic hybrid perovskites is presented. The maximal 3PA coefficient is predicted to be in the range of 2–7 cm3 GW?2 at 1100 nm, the largest values reported so far for any 2D and bulk semiconductors at room temperature. Excellent agreement between theory and the experimental findings unambiguously demonstrates a pivotal role in the enhancement of 3PA played by 2D excitons. The theory predicts that the resonant 3PA coefficient should be enhanced further by at least two orders of magnitude with very low temperature. The findings are essential for understanding giant 3PA arising from 2D excitons in layered hybrid perovskites and may open new pathways for highly efficient conversion from infrared light energy to either electrical energy or higher-frequency light emission/lasing.
关键词： nonlinear optics,three-photon absorbers,2D excitons,hybrid perovskites
更新于2025-09-04 15:30:14
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Stark shift of excitons and trions in two-dimensional materials
摘要： The effect of an external in-plane electric ?eld on neutral and charged exciton states in two-dimensional (2D) materials is theoretically investigated. These states are argued to be strongly bound, so that electron-hole dissociation is not observed up to high electric ?eld intensities. Trions in the anisotropic case of monolayer phosphorene are demonstrated to be especially robust under electric ?elds, so that ?elds as high as 100 kV/cm yield no signi?cant effect on the trion binding energy or probability density distribution. Polarizabilities of excitons are obtained from the parabolicity of numerically calculated Stark shifts. For trions, a fourth order Stark shift is observed, which enables the experimental veri?cation of hyperpolarizability in 2D materials, as observed in the highly excited states of the Rydberg series of atoms and ions.
关键词： Stark shift,polarizability,two-dimensional materials,electric field,excitons,trions,hyperpolarizability
更新于2025-09-04 15:30:14
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Experimental Evidence for “Hot Exciton” Thermally Activated Delayed Fluorescence Emitters
摘要： Contradiction between no effective photophysical experiments and high device results causes the “hot exciton” thermally activated delayed fluorescence (TADF) mechanism to be still a controversial question. Here, the steady and transient photophysical characterization combined with theoretical calculation based on 4,7-bis(9,9-dimethyl-9H-fluoren-2-yl)-5,6-difluorobenzo[c][1,2,5]thiadiazole (2F-BTH-DMF), 4,7-bis(9,9-dimethyl-9H-fluoren-2-yl)benzo[c][1,2,5]thiadiazole (BTH-DMF), and 5,6-bis(9,9-dimethyl-9H-fluoren-2-yl)benzo[c][1,2,5] thiadiazole (o-BTH-DMF) demonstrate that all the emitters exhibit TADF via reverse intersystem crossing (RISC) from “hot exciton” triplet excited state. The fast RISC process “hot exciton” mechanism affords a very short delayed lifetime (1 μs). Organic light-emitting diodes (OLEDs) based on these emitters exhibit high exciton utilization over 25% and the best device shows a maximum current efficiency of 31.02 cd A?1, maximum power efficiency of 27.85 lm W?1, and external quantum efficiency of 9.13%, which are the highest performances for reported OLEDs with “hot exciton” mechanism. The experimental evidence for fast RISC process via “hot exciton” triplet state and short delayed lifetime highlights the TADF emitters with “hot exciton” mechanism for high-performance OLEDs with very low efficiency roll-off.
关键词： hot excitons,reverse intersystem crossing,thermally activated delayed fluorescence,organic light-emitting devices
更新于2025-09-04 15:30:14