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A bulk scale process is implemented for the production of nanostructured film composites comprising unary or multi-component metal oxide nanoparticles dispersed in a suitable polymer matrix. The as-received nanoparticles, namely Al$$_2$$ 2 O$$_3$$ 3 , SiO$$_2$$ 2 and TiO$$_2$$ 2 and binary combinations, are treated following specific chemical and mechanical processes in order to be suspended at the optimal size and composition. Subsequently, a polymer extrusion technique is employed for the fabrication of each film, while the molten polymer is mixed with the treated metal oxide nanoparticles. Transmission and reflection measurements are performed in order to map the optical properties of the fabricated, nanostructured films in the UV, VIS and IR. The results substantiate the capability of the overall methodology to regulate the optical properties of the films depending on the type of nanoparticle formation which can be adjusted both in size and composition.

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The efficient harvesting of hot carrier energy in semiconductors is typically inhibited by their ultrafast thermalization process. Recently, highly promising experiments reported on the slowdown of the intraband relaxation in hybrid metal halide perovskites. In this work, we report on the presence of long-lived hot carriers in weakly confined colloidal nanocrystals (NCs) of formamidinium lead iodide perovskite (FAPbI3). The effect is apparent from the excitation-dependent lengthening of the rise time and broadening of the high-energy tail of the transient absorption bleaching signal, yielding a retardation of the carrier relaxation by 2 orders of magnitude compared to typical time scales in colloidal semiconductor NCs. Three distinct cooling stages are observed, occurring at sub-picosecond, ∼5 ps, and ∼40 ps time scales, which we attribute to scattering from LO-phonons, contribution from a hot phonon bottleneck effect and Auger heating, respectively. Thermalization appears also influenced by the FAPbI3 NCs purity, with trapping at unreacted precursor impurities further reducing the carrier energy loss rate. © 2017 American Chemical Society. 121 22 12434 12440

Epitaxial, highly ordered Sb:SnO2 nanowires were grown by the vapor–liquid–solid mechanism on m-, r- and a-Al2O3 between 700 °C and 1000 °C using metallic Sn and Sb with a mass ratio of Sn/Sb = 0.15 ± 0.05 under a flow of Ar and O2 at 1 ± 0.5 mbar. We find that effective doping and ordering can only be achieved inside this narrow window of growth conditions. The Sb:SnO2 nanowires have the tetragonal rutile crystal structure and are inclined along two mutually perpendicular directions forming a rectangular mesh on m-Al2O3 while those on r-Al2O3 are oriented in one direction. The growth directions do not change by varying the growth temperature between 700 °C and 1000 °C but the carrier density decreased from 8 × 1019 cm−3 to 4 × 1017 cm−3 due to the re-evaporation and limited incorporation of Sb donor impurities in SnO2. The Sb:SnO2 nanowires on r-Al2O3 had an optical transmission of 80% above 800 nm and displayed very long photoluminescence lifetimes of 0.2 ms at 300 K. We show that selective area location growth of highly ordered Sb:SnO2 nanowires is possible by patterning the catalyst which is important for the realization of novel nanoscale devices such as nanowire solar cells. 1 5 1980 1990

Colloidal quantum dots (CQDs) are typically decorated with organic molecules that provide surface passivation and colloidal solubility. An alternate but less studied surface functionalization approach via inorganic complexes can produce stable CQDs with attractive transport and optical properties. Further development of such all-inorganic CQD solids is dependent on the deeper understanding of the energetic and dynamic interactions of the new ligands with the CQD excitons. Herein, a series of four metal chalcogenide (MCC) ligands of the KzXS4 type were attached to PbS CQDs. Out of the four MCC complexes studied, we find that only K4GeS4 ligands yield robust PbS CQD films with bright photoluminescence (PL) in the solid state. A systematic spectroscopic investigation of the K4GeS4-capped CQD films provides evidence of the temperature-dependent ligand-mediated exciton delocalization and trapping processes. At low temperatures, efficient trapping at ligand-induced states is found to occur within similar to 6 ns after photoexcitation, followed by a considerably slower exciton back transfer to the CQD core. At elevated temperatures, the CQD films become photoconductive, providing evidence of exciton dissociation via carrier transfer within adjacent dots. The addition of a thin CdS shell suppresses the delocalization and trapping of excitons, resulting in brighter emission and significantly slower transient absorption and PL dynamics.

Pb-chalcogenide colloidal quantum dots (CQDs) are attractive materials to be used as tuneable laser media across the infrared spectrum. However, excessive nonradiative Auger recombination due to the presence of trap states outcompetes light amplification by rapidly annihilating the exciton population, leading to high gain thresholds. Here, a binary blend is employed of CQDs and ZnO nanocrystals in order to passivate the in-gap trap states of PbS-CQD gain medium. Using transient absorption, a fivefold increase is measured in Auger lifetime demonstrating the suppression of trap-assisted Auger recombination. By doing so, a twofold reduction is achieved in amplified spontaneous emission (ASE) threshold. Finally, by integrating the proposed binary blend to a distributed feedback (DFB) resonator, single-mode lasing emission is demonstrated at 1650 nm with a linewidth of 1.23 nm (0.62 meV), operating at a low lasing threshold of ≈385 μJ cm-2 . The Auger suppression in this system has allowed to achieve unprecedented lasing emission stability for a CQD laser with recorded continuous operation of 5 h at room temperature and ambient conditions.

We have grown Pb doped In2O3 nanowires at 800°C which have the cubic bixbyite crystal structure of In2O3 and contain orthorhombic α-PbO. These had resistances up to ≈10 Ω and exhibited photoluminescence at 2.5 eV but we observed the gradual emergence of infra red emission from 0.8 μm to 1.2 μm after processing under H2S between 200°C and 400°C. The resultant PbS/In2S3-3xO3x nanowires had similar resistances and consist of stacked crystals with sizes that depend on the Pb content. We discuss the potential of Pb for doping metal oxide semiconductors and the importance of PbS/In2O3 p-n tunnel junctions for solar cells. © 2015 Elsevier B.V. All rights reserved. 166 129 132 Cited By :1

Sb doped SnO2 nanowires have been grown via the vapor liquid solid mechanism on fused SiO2 at 800 °C and 1 mbar under a flow of Ar and O2 by using an excess of metallic Sb in conjunction with Sn. We obtain highly crystalline Sb:SnO2 nanowires with diameters of 100 nm, lengths up to 100 μm, and a tetragonal rutile crystal structure that contains Sb donor impurities as confirmed by Raman spectroscopy. The Sb:SnO2 nanowires have a maximum carrier density of 8 × 1018 cm–3 and conductivity of 2500 S/m at 300 K determined from THz conductivity spectroscopy and the Hall effect, which are significantly higher than 3 × 1016 cm–3 and 11 S/m in undoped SnO2 nanowires. The one-dimensional electron gas charge distribution has a maximum at the core but extends all the way up to the surface as shown via the self-consistent solution of the Poisson-Schrödinger equations in contrast to the case of undoped SnO2 where the surface depletion leads to a confinement of the charge distribution to the core by taking into account the energetic position of the Fermi level with respect to the conduction band at the surface. We show that the Sb impurities are not incorporated into the SnO2 lattice through the Au particles, while higher growth temperatures between 900 to 1000 °C and/or lower growth pressures between 10–2 to 10–1 mbar do not result into the incorporation of Sb impurities in the SnO2 nanowires. This is attributed to the depletion of metallic Sb during the temperature ramp, before the onset of one-dimensional growth and/or the re-evaporation of Sb impurities arriving on the surface of the SnO2 nanowires and implies a fundamental doping limitation that is challenging to overcome especially in view of the fact the one-dimensional growth was suppressed under a significant excess of Sb. 122 39 22709 22716

SnO2 nanowires were grown on Si, fused SiO2, and C fibers by the vapor–liquid–solid mechanism at 800 °C and 10–1 mbar, and SnO2/PbO core–shell nanowires were obtained by the deposition of 50 nm Pb over the SnO2 nanowires followed by annealing between 100 and 200 °C. The SnO2/PbO nanowires have diameters of 100–300 nm and lengths up to 100 μm and consist mainly of tetragonal rutile SnO2 and PbO. Higher temperatures between 300 and 500 °C resulted in the formation of Pb2O3 and Pb3O4 with monoclinic and orthorhombic crystal structures, but the SnO2/PbO and SnO2/Pb2O3 nanowires had low conductivities of 10–1 S/cm. In contrast, highly conductive SnO2/PbO2 nanowires were obtained by electrodeposition of PbO2 in 0.3 M HNO3 and 1 M Pb(NO3)2 (aq). PbO2 forms a straddling-type heterojunction with SnO2, and the one-dimensional (1D) electron gas distribution is confined in the PbO2 shell for sufficiently thick shells, as shown by the self-consistent solution of the Poisson–Schrödinger equations in the effective mass approximation. The SnO2/PbO2 nanowires exhibit an open-circuit potential of 1.8 V versus C-fiber networks in 5 M H2SO4 (aq) and show symmetric cyclic voltammetry curves, suggesting a suppression of the redox reactions related to SnO2 and a high specific capacity of 206 mAh/g. We discuss the potential of both SnO2 and SnO2/PbO2 nanowires on C fibers for the attainment of even higher specific capacity in a Li-ion battery. 122 45 25813 25821

Epitaxial, highly ordered Sb:SnO

Glucocorticoid metabolism prior to receptor binding represents an important regulatory step that governs their action. The expression and activity of many different enzymes involved in this process have been described, including the isozymes of 11β-hydroxysteroid dehydrogenase and the A-ring reductases (5α- and 5β-reductase). Mutations in the genes encoding these enzymes cause specific pathological phenotypes and dysregulation of their activity and expression has been implicated in the pathogenesis of common clinical conditions.

36th European Photovoltaic Solar Energy Conference and Exhibition; 696-698, Carrier dynamics with femtosecond resolution are investigated in the spectral region of InGaP/InGaAs in InGaP/InGaAs/Ge multi-junction solar cells indicating picosecond scale coupling effects between both junctions. Picosecond scale coupling between top and middle junction is evident by the presence of two peaks in the timeresolved differential reflection with 3.1 eV excitation and 1.38 eV probing energy at low temperatures (77 K). Measurements are repeated at higher temperatures (300 K) but no evidence of picosecond scale coupling effects in the material is found in this case. Moreover, measurements with 1.55 eV excitation are carried out aiming at the excitation of carriers far below the band-gap edge of the top junction and thus without the presence of coupling in the tandem.

The slowdown of carrier cooling in lead halide perovskites (LHP) may allow the realization of efficient hot carrier solar cells. Much of the current effort focuses on the understanding of the mechanisms that retard the carrier relaxation, while proof-of-principle demonstrations of hot carrier harvesting have started to emerge. Less attention has been placed on the impact that the energy and momentum relaxation slowdown imparts on the spontaneous and stimulated light-emission process. LHP nanocrystals (NCs) provide an ideal testing ground for such studies as they exhibit bright emission and high optical gain, while the carrier cooling bottleneck is further pronounced compared to their bulk analogues due to confinement. Herein, the luminescent properties of CsPbBr3, FAPbBr3, and FAPbI3 NCs in the strong photoexcitation regime are investigated. In the former two NC systems, amplified spontaneous emission is found to dominate over the radiative recombination at average carrier occupancy per nanocrystal larger than 5–10. On the other hand, under the same photoexcitation conditions in the FAPbI3 NCs, a longer lived population of hot carriers results in a competition between hot luminescence, stimulated emission, and defect recombination. The dynamic interplay between the aforementioned three emissive channels appears to be influenced by various experimental and material parameters that include temperature, material purity, film morphology, and excitation pulse width and wavelength., ACS Nano, 13 (5), ISSN:1936-0851, ISSN:1936-086X

The structural, optical, and electrical transport properties of nanowires obtained by the deposition of Cu over Sn doped In2O3 and SnO2 nanowires followed by processing under H2S between 100 and 500°C have been investigated for their use in quantum dot sensitized solar cells. We find that the CuS/Sn:In2O3 nanowires obtained between 100 and 200°C consist of hexagonal CuS and cubic In2O3 but higher temperatures lead to the formation of Cu0.23In2.59S4 nanowires. Moreover, we observed the existence of SnO2 quantum dots in tetragonal Cu2SnS3 nanowires obtained at 400-500°C which are responsible for ultraviolet emission at 3.65 eV and a breakdown of the dipole forbidden rule in SnO2.The CuS/Sn:In2O3 nanowires obtained at lower temperatures exhibit better rectifying current-voltage characteristics and higher currents, but we did not observe negative differential resistance, as expected from a p-n tunnel junction, although this occurred by bringing Sn:In2O3 nanowires in weak contact with p-type CuS, similar to a cat's whisker device. We discuss the origin of the negative differential resistance which was also observed in connection with the TiO2 barriers deposited on the transparent conducting oxide anode and its importance for quantum dot sensitized solar cells. © 2015 American Chemical Society. 120 1 11 20 Cited By :2