Although human eyes are quite insensitive to ultraviolet (UV) light, most of the longer wavelength UV light (the UV-A band between 320 and 400 nm) does reach the earth surface and after prolonged exposure, the radiation can cause health concerns especially skin cancer. Therefore, it is extremely important to explore ways to effectively monitor the radiation. Herein we report for the fi rst time a new high-performance UV photodetector made of an individual Nb 2 O 5 nanobelt. Quasi-aligned Nb 2 O 5 nanobelts 100-500 nm wide and 2-10 μ m long were synthesized using a hydrothermal treatment of a niobium foil in a KOH solution followed by proton exchange and calcination treatment. A nanostructured photodetector was constructed from an individual Nb 2 O 5 nanobelt and its optoelectronic properties were evaluated. The detector exhibited linear photocurrent characteristics, excellent light selectivity, and high external quantum-effi ciency (EQE) of 6070%. Long-term stability of the photocurrent over a period of 2500 s at an applied voltage of 1.0 V was achieved. The photodetector performance was further enhanced by improving the crystallinity and eliminating the defects in the Nb 2 O 5 nanobelt crystals. These excellent optoelectronic properties demonstrate that Nb 2 O 5 nanobelts are suitable for visible-blind UV-light sensors and optoelectronic circuits, especially those operating in the UV-A range.

Tetrapod-shaped CdSe nanocrystals have been successfully synthesized in high yields using a simple method of controlling the protonic acidity of the reaction system. A possible growth mechanism is discussed on the basis of the surface modification of H+ present. The crystal structure of CdSe tetrapods is determined by high-resolution transmission electron microscopy analysis to have a zinc blende core at the center with four wurtzite arms growing out from the core along four [111] directions. The electronic structure of CdSe tetrapods is studied theoretically in comparison with that of spherical dots.

Fluorescence of the cyanine dye Thiazole Orange (TO) is quenched by intramolecular twisting in the excited state. In polypeptide nucleic acids, a vibrational progression in a 1400 cm(-1) mode depends on base pairing, from which follows that the high-frequency displacement is coupled to the twist coordinate. The coupling is intrinsic to TO. This is shown by femtosecond fluorescence upconversion and transient absorption spectroscopy with the dye in methanol solution. Narrow emission from the Franck-Condon state shifts to the red and broadens within 100 fs. The radiative rate does not decrease during this process. Vibrational structure builds up on a 200 fs time scale; it is assigned to asymmetric stretching activity in the methine bridge. Further Stokes shift and decay are observed over 2 ps. Emission from the global S(1) minimum is discovered in an extremely wide band around 12 000 cm(-1). As the structure twists away from the Franck-Condon region, the mode becomes more displaced and overlap with increasingly higher vibrational wave functions of the electronic ground state is achieved. Twisting motion is thus leveraged into a fast-shrinking effective energy gap between the two electronic states, and internal conversion ensues.