Low-threshold amplified spontaneous emission and lasing from colloidal nanocrystals of caesium lead halide perovskites.

Metal halide semiconductors with perovskite crystal structures have recently emerged as highly promising optoelectronic materials. Despite the recent surge of reports on microcrystalline, thin-film and bulk single-crystalline metal halides, very little is known about the photophysics of metal halides in the form of uniform, size-tunable nanocrystals. Here we report low-threshold amplified spontaneous emission and lasing from ∼10 nm monodisperse colloidal nanocrystals of caesium lead halide perovskites CsPbX3 (X=Cl, Br or I, or mixed Cl/Br and Br/I systems). We find that room-temperature optical amplification can be obtained in the entire visible spectral range (440-700 nm) with low pump thresholds down to 5±1 µJ cm(-2) and high values of modal net gain of at least 450±30 cm(-1). Two kinds of lasing modes are successfully observed: whispering-gallery-mode lasing using silica microspheres as high-finesse resonators, conformally coated with CsPbX3 nanocrystals and random lasing in films of CsPbX3 nanocrystals.

High infrared photoconductivity in films of arsenic-sulfide-encapsulated lead-sulfide nanocrystals.

Highly photoconductive thin films of inorganic-capped PbS nanocrystal quantum dots (QDs) are reported. Stable colloidal dispersions of (NH4)3AsS3-capped PbS QDs were processed by a conventional dip-coating technique into a thin homogeneous film of electronically coupled PbS QDs. Upon drying at 130 °C, (NH4)3AsS3 capping ligands were converted into a thin layer of As2S3, acting as an infrared-transparent semiconducting glue. Photodetectors obtained by depositing such films onto glass substrates with interdigitate electrode structures feature extremely high light responsivity and detectivity with values of more than 200 A/W and 1.2×10(13) Jones, respectively, at infrared wavelengths up to 1400 nm. Importantly, these devices were fabricated and tested under ambient atmosphere. Using a set of time-resolved optoelectronic experiments, the important role played by the carrier trap states, presumably localized on the arsenic-sulfide surface coating, has been elucidated. Foremost, these traps enable a very high photoconductive gain of at least 200. The trap state density as a function of energy has been plotted from the frequency dependence of the photoinduced absorption (PIA), whereas the distribution of lifetimes of these traps was recovered from PIA and photoconductivity (PC) phase spectra. These trap states also have an important impact on carrier dynamics, which led us to propose a kinetic model for trap state filling that consistently describes the experimental photoconductivity transients at various intensities of excitation light. This model also provides realistic values for the photoconductive gain and thus may serve as a useful tool to describe photoconductivity in nanocrystal-based solids.

Integration, photostability and spontaneous emission rate enhancement of colloidal PbS nanocrystals for Si-based photonics at telecom wavelengths.

We experimentally investigate PbS nanocrystal (NC) photoluminescence (PL) coupled to all-integrated Si-based ring resonators and waveguides at telecom wavelengths. Dissolving the NCs into Novolak polymer significantly improves their stability in ambient atmosphere. Polymer-NC blends of various NC concentrations can be applied to and removed from the same device. For NC concentrations up to 4vol%, the spontaneous emission rate into ring-resonator modes is enhanced by a factor of ~13 with respect to that into a straight waveguide. The PL intensity shows a linear dependence on the excitation intensity up to 1.64kW/cm(2) and stable quality factors of ~2500.

From highly monodisperse indium and indium tin colloidal nanocrystals to self-assembled indium tin oxide nanoelectrodes.

Indium tin oxide (ITO) nanopatterned electrodes are prepared from colloidal solutions as a material saving alternative to the industrial vapor phase deposition and top down processing. For that purpose highly monodisperse In(1-x)Sn(x) (x < 0.1) colloidal nanocrystals (NCs) are synthesized with accurate size and composition control. The outstanding monodispersity of the NCs is evidenced by their self-assembly properties into highly ordered superlattices. Deposition on structured substrates and subsequent treatment in oxygen plasma converts the NC assemblies into transparent electrode patterns with feature sizes down to the diameter of single NCs. The conductivity in these ITO electrodes competes with the best values reported for electrodes from ITO nanoparticle inks.

[Dynamic and static maximum strength in closed kinetic chain movements. Trunkflexion/-extension and -rotation]. / Dynamische und statische Maximalkraft in der geschlossenen Kette bei Rumpfflexion/-extension und Rumpfrotation.

BACKGROUND: Isokinetics offer a range of applications in hospital, therapy and training. The aim of this study was to determine, how the torques (Nm) of trunk flexion/-extension and trunk rotation behave at different contraction types (eccentrically, isometrically, concentrically) and different speeds. METHOD: Therefore different isokinetic testing procedures were performed in 34 subjects (17 female). RESULTS: The angle (°) in which the max. torque (Nm) is measured is inconsistent for the trunk flexion. Here the maximum values for different contraction forms and speeds of movement were found between +1,73 and -19,24°. For extension, however, the max values were achieved between +6,12 and +17,42° (hip angle < 90°). For trunk rotation the highest values were found, when the torso was rotated to the opposite side of the movement. For example, at left rotation the maximum values were found between -12,91 and -18,97°. As a recommendation for the test speed 30°/sec. is stated for both movements concentric and eccentric, since these data have a high accuracy (best interpretation) and this speed was felt to be pleasant. The highest torques were usually measured at 30°/sec. eccentric, predominant values for 15°/sec. eccentric and isometric were significantly lower. CONCLUSION: These results should contribute to an efficient application of the IsoMed 2000 testing and training device in clinical, therapeutical and sport scientific fields.