In materials showing reverse saturable absorption (RSA), the optical absorbance increases as the power of the light incident on them increases. To date, RSA has only been observed when very intense light sources, such as short-pulse lasers, are used. Here, we show that hydroxyl steroidal matrices embedding properly designed aromatic molecules as acceptors and transition-metal complexes as donors exhibit high RSA on exposure to weak incoherent light at room temperature and in air. Accumulation by photosensitization of long-lived room-temperature triplet excitons in acceptors with a large triplet-triplet absorption coefficient allows a nonlinear increase in absorbance also under low-power irradiation conditions. As a consequence, continuous exposure to weak light significantly decreases the transmittance of thin films fabricated with these compounds. These optical limiting properties may be used to protect eyes and light sensors from exposure to intense radiation generated by incoherent sources and for other light-absorption applications that have not been realized with conventional RSA materials.

Nanoparticles of I-III-VI semiconductors are promising candidates for novel non-toxic fluorescent materials. However, removal of defect levels responsible for their broad-band emission has not been successful to date. The present study demonstrates, for the first time, the coating of core AgInS 2 nanoparticles-one of the I-III-VI group semiconductors with a bandgap in the visible region-with III-VI group semiconductors. The AgInS 2 /InS x and AgInS 2 /GaS x (x = 0.8-1.5) core/shell structures generate intense narrow-band photoluminescence originating from a band-edge transition at a wavelength shorter than that of the original defect emission. Microscopic analyses reveal that the GaS x shell has an amorphous nature, which is unexpected for typical shell materials such as crystalline lattice-matching ZnS. Singleparticle spectroscopy shows that the average linewidth of the band-edge photoluminescence is as small as 80.0 meV (or 24 nm), which is comparable with that of industry-standard II-VI semiconductor quantum dots. In terms of photoluminescence quantum yield, a value of 56% with nearly single-band emission has been achieved as a result of several modifications to the reaction conditions and post-treatment to the core/shell nanoparticles. This work indicates the increasing potential of AgInS 2 nanoparticles for use as practical cadmium-free quantum dots.

The ability to perceive geomagnetic fields (GMFs) represents a fascinating biological phenomenon. Studies on transgenic flies have provided evidence that photosensitive Cryptochromes (Cry) are involved in the response to magnetic fields (MFs). However, none of the studies tackled the problem of whether the Cry-dependent magnetosensitivity is coupled to the sole MF presence or to the direction of MF vector. In this study, we used gene silencing and a directional MF to show that mammalian-like Cry2 is necessary for a genuine directional response to periodic rotations of the GMF vector in two insect species. Longer wavelengths of light required higher photon fluxes for a detectable behavioral response, and a sharp detection border was present in the cyan/green spectral region. Both observations are consistent with involvement of the FADox, FAD•− and FADH -redox forms of flavin. The response was lost upon covering the eyes, demonstrating that the signal is perceived in the eye region. Immunohistochemical staining detected Cry2 in the hemispherical layer of laminal glia cells underneath the retina. Together, these findings identified the eye-localized Cry2 as an indispensable component and a likely photoreceptor of the directional GMF response. Our study is thus a clear step forward in deciphering the in vivo effects of GMF and supports the interaction of underlying mechanism with the visual system. magnetoreception | cryptochrome | light spectrum | locomotor activity | circadian genes

We use a novel fluorescence polarization microscope in combination with molecular dynamics calculations to determine the conformation of individual isolated chains of the conjugated polymer MEH-PPV. We found a narrow distribution of defect cylinder conformations in a poor-solvent matrix and two types of defect coil conformations in a good-solvent matrix. The conformations were related to photophysical properties of MEH-PPV by measuring fluorescence intermittency on the same chains. We obtained direct evidence that the photophysics is determined by the chain conformations and that small changes in the polymer microscopic structure can qualitatively affect the photophysical properties.

Binary crystalline solids via solution casting under rapid drying conditions were found to show efficient triplet–triplet annihilation upconversion by suppressing the segregation of the components.