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

Structural effects on the luminescence properties of CsPbI3 nanocrystals

Metal halide perovskite nanocrystals (NCs) are promising for photovoltaic and light-emitting applications. Due to the softness of their crystal lattice, structural modifications have a critical impact on their optoelectronic properties. Here we investigate the size-dependent optoelectronic properties of CsPbI3 NCs ranging from 7 to 17 nm, employing temperature and pressure as thermodynamic variables to modulate the energetics of the system and selectively tune the interatomic distances. By temperature-dependent photoluminescence spectroscopy, we have found that luminescence quenching channels exhibit increased non-radiative losses and weaker exciton-phonon coupling in bigger particles, in turn affecting the luminescence efficiency. Through pressure-dependent measurements up to 2.5 GPa, supported by XRD characterization, we revealed a NC-size dependent solid-solid phase transition from the γ-phase to the δ-phase. Importantly, the optical response to these structural changes strongly depends on the size of the NC. Our findings provide an interesting guideline to correlate the size and structural and optoelectronic properties of CsPbI3 NCs, important for engineering the functionalities of this class of soft semiconductors

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

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

5-Oxazolones. Part V. Reaction of 4-alkylidene-5(4H)-oxazolones with ethyl 3-oxo-4-triphenylphosphoranylidene-butyrate

The reaction of 4-alkylidene-5(4H)-oxazolones 2a-e with ethyl 3-oxo-4-triphenylphosphoranylidene-butyrate 1 affords dihydrobenzoxazoles 3a-c and the diastereoisomeric 1,3-cyclohexanedione ylides 4a-e and 5a-e. 3a is oxidized to the corresponding benzoxazoles 7a,b with iodine

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

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

Structural effects on the luminescence properties of CsPbI3 nanocrystals

Metal halide perovskite nanocrystals (NCs) are promising for photovoltaic and light-emitting applications. Due to the softness of their crystal lattice, structural modifications have a critical impact on their optoelectronic properties. Here we investigate the size-dependent optoelectronic properties of CsPbI3 NCs ranging from 7 to 17 nm, employing temperature and pressure as thermodynamic variables to modulate the energetics of the system and selectively tune the interatomic distances. By temperature-dependent photoluminescence spectroscopy, we have found that luminescence quenching channels exhibit increased non-radiative losses and weaker exciton-phonon coupling in bigger particles, in turn affecting the luminescence efficiency. Through pressure-dependent measurements up to 2.5 GPa, supported by XRD characterization, we revealed a NC-size dependent solid-solid phase transition from the γ-phase to the δ-phase. Importantly, the optical response to these structural changes strongly depends on the size of the NC. Our findings provide an interesting guideline to correlate the size and structural and optoelectronic properties of CsPbI3 NCs, important for engineering the functionalities of this class of soft semiconductors