Mixed-halide perovskites have emerged as promising materials for optoelectronics due to their tunable band gap in the entire visible region. A challenge remains, however, in the photoinduced phase segregation, narrowing the band gap of mixed-halide perovskites under illumination thus restricting applications. Here, we use a combination of spatially resolved and bulk measurements to give an in-depth insight into this important yet unclear phenomenon. We demonstrate that photoinduced phase segregation in mixed-halide perovskites selectively occurs at the grain boundaries rather than within the grain centers by using shear-force scanning probe microscopy in combination with confocal optical spectroscopy. Such difference is further evidenced by light-biased bulk Fourier-transform photocurrent spectroscopy, which shows the iodine-rich domain as a minority phase coexisting with the homogeneously mixed phase during illumination. By mapping the surface potential of mixed-halide perovskites, we evidence the higher concentration of positive space charge near the grain boundary possibly provides the initial driving force for phase segregation, while entropic mixing dominates the reverse process. Our work offers detailed insight into the microscopic processes occurring at the boundary of crystalline perovskite grains and will support the development of better passivation strategies, ultimately allowing the processing of more environmentally stable perovskite films.

The dynamics of excitons in individual semiconducting single-walled carbon nanotubes was studied using time-resolved photoluminescence (PL) spectroscopy. The PL decay from tubes of the same n; m type was found to be monoexponential, however, with lifetimes varying between less than 20 and 200 ps from tube to tube. Competition of nonradiative decay of excitons is facilitated by a thermally activated process, most likely a transition to a low-lying optically inactive trap state that is promoted by a lowfrequency phonon mode.

The orientation of the S 1 r S 0 π,π* transition dipole moments of oxonine (Ox + ), pyronine (Py + ), and POPOP (5,5′-diphenyl-2,2′-p-phenylenebis(oxazole)) in the channels of zeolite L crystals was investigated by means of fluorescence microscopy and single-crystal imaging. Qualitative observations led to the result that the transition moment of POPOP is aligned along the c-axis of the hexagonal crystals whereas the fluorescence of Ox + and Py + is not. More detailed investigations on Ox + showed a cone-shaped distribution of the transition moments with a half-cone angle of 72°. The orientation of the transition dipole moment for all of these molecules is parallel to the molecules' long axis. We found by means of space-filling arguments that POPOP, the van der Waals length of which is about 21 Å, can only be aligned along the channel axis. This is in full agreement with the observed fluorescence anisotropy. For Ox + and Py + , geometrical arguments based on the zeolite L structure give room for only two possible arrangements of the molecules' long axis: a half cone angle of up to 40°for Ox + and up to 30°for Py + , and an angle of about 90°for both of them with respect to the c-axis of zeolite L. The surprising discrepancy between geometrical considerations and the results of the fluorescence measurements can be explained by assuming that Ox + and Py + are exposed to a considerable anisotropic electrical field in the zeolite channels.

Background: At depths below 10 m, reefs are dominated by blue-green light because seawater selectively absorbs the longer, 'red' wavelengths beyond 600 nm from the downwelling sunlight. Consequently, the visual pigments of many reef fish are matched to shorter wavelengths, which are transmitted better by water. Combining the typically poor long-wavelength sensitivity of fish eyes with the presumed lack of ambient red light, red light is currently considered irrelevant for reef fish. However, previous studies ignore the fact that several marine organisms, including deep sea fish, produce their own red luminescence and are capable of seeing it.

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BackgroundStomatal guard cells monitor and respond to environmental and endogenous signals such that the stomatal aperture is continually optimised for water use efficiency. A key signalling molecule produced in guard cells in response to plant hormones, light, carbon dioxide and pathogen-derived signals is hydrogen peroxide (H2O2). The mechanisms by which H2O2 integrates multiple signals via specific signalling pathways leading to stomatal closure is not known.Principal FindingsHere, we identify a pathway by which H2O2, derived from endogenous and environmental stimuli, is sensed and transduced to effect stomatal closure. Histidine kinases (HK) are part of two-component signal transduction systems that act to integrate environmental stimuli into a cellular response via a phosphotransfer relay mechanism. There is little known about the function of the HK AHK5 in Arabidopsis thaliana. Here we report that in addition to the predicted cytoplasmic localisation of this protein, AHK5 also appears to co-localise to the plasma membrane. Although AHK5 is expressed at low levels in guard cells, we identify a unique role for AHK5 in stomatal signalling. Arabidopsis mutants lacking AHK5 show reduced stomatal closure in response to H2O2, which is reversed by complementation with the wild type gene. Over-expression of AHK5 results in constitutively less stomatal closure. Abiotic stimuli that generate endogenous H2O2, such as darkness, nitric oxide and the phytohormone ethylene, also show reduced stomatal closure in the ahk5 mutants. However, ABA caused closure, dark adaptation induced H2O2 production and H2O2 induced NO synthesis in mutants. Treatment with the bacterial pathogen associated molecular pattern (PAMP) flagellin, but not elf peptide, also exhibited reduced stomatal closure and H2O2 generation in ahk5 mutants.SignificanceOur findings identify an integral signalling function for AHK5 that acts to integrate multiple signals via H2O2 homeostasis and is independent of ABA signalling in guard cells.

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We present a new method for the imaging of single metallic nanoparticles that provides information about their shape and orientation. Using confocal microscopy in combination with higher order laser modes, scattering images of individual particles are recorded. Gold nanospheres and nonorods render characteristic patterns reflecting the different particle geometries. In the case of nanorods, the scattering patterns also reveal the orientation of the particles. This novel technique provides a promising tool for the visualization of nonbleaching labels in the biosciences.