34 research outputs found
Ultrafast charge carrier dynamics in quantum confined 2D perovskite
We studied the charge carrier dynamics in 2D perovskite NBT2PbI4 by ultrafast optical pump-THz probe spectroscopy. We observed a few ps long relaxation dynamics that can be ascribed to the band to band carrier recombination, in the absence of any contribution from many-body and trap assisted processes. The transient conductivity spectra show that the polaron dynamics is strongly modulated by the presence of a rich exciton population. The polarization field resulting from the exciton formation acts as the source of a restoring force that localizes polarons. This is revealed by the presence of a negative imaginary conductivity. Our results show that the dynamics of excitons in 2D perovskites at room temperature can be detected by monitoring their effect on the conductivity of the photoinduced polaronic carrier
Lasing in Two-Dimensional Tin Perovskites
Two-dimensional (2D) perovskites have been proposed as materials capable of improving the stability and surpassing the radiative recombination efficiency of three-dimensional perovskites. However, their luminescent properties have often fallen short of what has been expected. In fact, despite attracting considerable attention for photonic applications during the last two decades, lasing in 2D perovskites remains unclear and under debate. Here, we were able to improve the optical gain properties of 2D perovskite and achieve optically pumped lasing. We show that the choice of the spacer cation affects the defectivity and photostability of the perovskite, which in turn influences its optical gain. Based on our synthetic strategy, we obtain PEA2SnI4 films with high crystallinity and favorable optical properties, resulting in amplified spontaneous emission (ASE) with a low threshold (30 μJ/cm2), a high optical gain above 4000 cm-1 at 77 K, and ASE operation up to room temperature
Effect of electronic doping and traps on carrier dynamics in tin halide perovskites
Tin halide perovskites have recently emerged as promising materials for low band gap solar cells. Much effort has been invested on controlling the limiting factors responsible for poor device efficiencies, namely self-p-doping and tin oxidation. Both phenomena are related to the presence of defects; however, full understanding of their implications in the optoelectronic properties of the material is still missing. We provide a comprehensive picture of the competing radiative and non-radiative recombination processes in tin-based perovskite thin films to establish the interplay between doping and trapping by combining photoluminescence measurements with trapped-carrier dynamic simulations and first-principles calculations. We show that pristine Sn perovskites, i.e. sample processed with commercially available SnI2 used as received, exhibit extremely high radiative efficiency due to electronic doping which boosts the radiative band-to-band recombination. Contrarily, thin films where Sn4+ species are intentionally introduced show drastically reduced radiative lifetime and efficiency due to a dominance of Auger recombination at all excitation densities when the material is highly doped. The introduction of SnF2 reduces the doping and passivates Sn4+ trap states but conversely introduces additional non-radiative decay channels in the bulk that fundamentally limit the radiative efficiency. Overall, we provide a qualitative model that takes into account different types of traps present in tin-perovskite thin films and show how doping and defects can affect the optoelectronic properties
Study of shock waves generation, hot electron production and role of parametric instabilities in an intensity regime relevant for the shock ignition
We present experimental results at intensities relevant to Shock Ignition
obtained at the sub-ns Prague Asterix Laser System in 2012 . We studied shock waves
produced by laser-matter interaction in presence of a pre-plasma. We used a first beam at
1ω (1315 nm) at 7 × 10 13 W/cm 2 to create a pre-plasma on the front side of the target and
a second at 3ω (438 nm) at ∼ 10 16 W/cm 2 to create the shock wave. Multilayer targets
composed of 25 (or 40 μm) of plastic (doped with Cl), 5 μm of Cu (for Kα diagnostics)
and 20 μm of Al for shock measurement were used. We used X-ray spectroscopy of Cl
to evaluate the plasma temperature, Kα imaging and spectroscopy to evaluate spatial and
spectral properties of the fast electrons and a streak camera for shock breakout measurements.
Parametric instabilities (Stimulated Raman Scattering, Stimulated Brillouin Scattering and
Two Plasmon Decay) were studied by collecting the back scattered light and analysing its
spectrum. Back scattered energy was measured with calorimeters. To evaluate the maximum
pressure reached in our experiment we performed hydro simulations with CHIC and DUED
codes. The maximum shock pressure generated in our experiment at the front side of the
target during laser-interaction is 90 Mbar. The conversion efficiency into hot electrons was
estimated to be of the order of ∼ 0.1% and their mean energy in the order ∼50 keV.
Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distributio
Metal Coordination Sphere Deformation Induced Highly Stokes-Shifted, Ultra Broadband Emission in 2D Hybrid Lead-Bromide Perovskites and Investigation of Its Origin
Published studies of layered (2D) (100)-oriented hybrid lead-bromide perovskites evidence a correlation between increased inter-octahedral (Pb-Br-Pb) distortions and the appearance of broadband white light emission. However, the impact of distortions within their constituent [PbBr6]4- octahedra has yet to be assessed. Herein, we report two new (100)-oriented 2D Pb-Br perovskites, whose structures display unusually high intra-octahedral distortions, whilst retaining minimal inter-octahedral distortions. Using a combination of temperature-dependent, power-dependent and time-resolved photoluminescence spectroscopic measurements, we show that increased intra-octahedral distortion induces exciton localization processes and leads to formation of multiple photoinduced emissive colour centres. Ultimately, this leads to highly Stokes-shifted, ultrabroad white light emission at room temperature
Limited diagnostic value of lymphocytic karyotype in primary amenorrhea with streak gonads.
Cytogenetic data represent a first line diagnostic aid in gonadal dysgenesis. Generally, the results of a peripheral blood examination reflect the genotypic alteration of the patient. Nevertheless, on occasion one may encounter cases in which clinical and hormonal evidence suggestive of dysgenesis is not accompanied by an anomalous chromosomal finding, upon cytogenetic analysis of the peripheral blood. In these cases, a cytogenetic alteration may be present in cellular components of the ovary and the cutis. In the light of the above, two patients presenting with primary hypergonadotropic amenorrhea, streak gonads and normal peripheral karyotype are described. In one patient presenting with phenotype alterations, ovarian wedge biopsy via laparotomy followed by cytogenetic analysis of ovarian tissue and tissue from the cutis revealed a 45,X/46,XX-type mosaicism. In the other patient, the ovarian cytogenetic findings were unremarkable. Extending chromosomal analysis to several tissues, beyond the peripheral level, in selected cases, is discussed
Non-mosaic isodicentric X-chromosome in a patient with secondary amenorrhea.
An isodicentric X-chromosome idic(X) (pter----q26.1::q26.1----pter) was found in lymphocytes and ovarian tissue of a 40-year-old female patient with secondary amenorrhea. No mosaicism was observed. The phenotype-karyotype correlation of our case and of previously described non-mosaic cases of idic(X) (q::q) with different breakpoints is discussed
Time-resolved terahertz spectroscopy for probing the effects of low-temperature annealing on CsPbBr3evaporated thin-films
Semi-analytical approaches to study hot electrons in the shock ignition regime
Hot electrons role in shock generation and energy deposition to hot dense
core is crucial for the shock ignition scheme implying the need for their
characterization at laser intensities of interest for shock ignition. In this
paper we analyze the experimental results obtained at the PALS laboratory and
provide an estimation of hot electrons temperature and conversion efficiency
using a semi analytical approach, including Harrach-Kidder's model.Comment: Has been accepted in Physics of Plasma journa