Temperature Characterization of Unipolar-Doped Electroluminescence in Vertical GaN/AlN Heterostructures

An electroluminescence (EL) phenomenon in unipolar-doped GaN/AlN/GaN double-barrier heterostructures—without any p-type contacts—was investigated from 4.2 K to 300 K. In the range of 200–300 K, the extracted peak photon energies agree with the Monemar formula. In the range of 30 to 200 K, the photon energies are consistent with A-exciton emission. At 4.2 K, the exciton type likely transforms into B-exciton. These studies confirm that the EL emission comes from a cross-bandgap (or band-to-band) electron-hole radiative recombination and is excitonic. The excitons are formed by the holes generated through interband tunneling and the electrons injected into the GaN emitter region of the GaN/AlN heterostructure devices.

Blue flower coloration of Corydalis ambigua requires ferric ion and kaempferol glycoside

Corydalis ambigua (Japanese name, Ezoengosaku) flowers bloom with blue to purplish petals in early spring in Hokkaido prefecture. In this study, a mechanism for blue petal coloration by ferric ions and keampferol glycoside was elucidated. Blue petals and cell sap exhibited similar visible (Vis) spectra, with λmax at approximately 600 nm and circular dichroism (CD) with positive exciton-type Cotton effects in the Vis region. Analysis of the organic components of the petals confirmed cyanidin 3-O-sambubioside and kaempferol 3-O-sambubioside as the major flavonoids. Mg, Al, and Fe were detected in petals using atomic emission spectroscopy. Color, Vis absorption, and CD consistent with those of blue petals were reproduced by mixing cyanidin 3-O-sambubioside, kaempferol 3-O-sambubioside, and Fe3+ in a buffered aqueous solution at pH 6.5. Both Fe3+ and flavonol were essential for blue coloration.

Delicate modulation of triplet energy levels for activating “hot excitons” channels in deep red AIEgens

A delicate modulation of triplet excited-state energy levels in deep-red AIEgens is reported for designing “hot exciton”-type OLED emitters with high performance.

NaV2O5: AN EXOTIC EXCITON SYSTEM

We show that the phase transition which sodium vanadate undergoes at Tc=34 K is driven by a charge ordering. The relevant effective Hamiltonian is of the Frenkel exciton type, with a very large bandwidth to molecular energy ratio. This causes stron non-Heitler-London effects and a temperature dependent gap that vanishes at Tc. In addition to the phase transition, the model qualitatively explains the observed absorption spectrum and the anomaly in the static dielectric constant. Within our model, the observed spin-gap opening at Tc results from exciton-spinon coupling.

Chiroptical properties of chlorophyll-protein complexes separated on Deriphat/polyacrylamide gel

Circular dichroism (c.d.) was measured for four chlorophyll-protein complexes, resolved from sodium dodecyl sulphate extracts of chloroplasts by electrophoresis in polyacrylamide gel containing Deriphat 160 (disodium N-dodecyl beta-imidopropionate), a zwitterionic detergent. The slowest-band (1) complex was found to be identical with the complex CP1 as found on electrophoresis in the presence of anion detergent, but it was in a much higher yield (30% of the chlorophyll a). In band-2 and -3 protein complexes a c.d. pattern described for the complex CP2 could be recognized. Another c.d. component of a split-exciton type with extrema at 680 (-) and 669 (+)nm, together with evidence of disorganized chlorophyll, was found in band-2, -3 and -4 complexes. When a barley (Hordeum vulgare) mutant lacking chlorophyll b was examined, only bands 1 and 4 were obtained, and the c.d. of the band-4 complex was much less affected by disorganized chlorophyll. C.D. spectra resembling that of this band-4 complex could be generated by subtracting the c.d. of complex CP1 from the c.d. of photochemically active mutant chloroplast fragments, or by subtracting the c.d. of complexes CP1 and CP2 from pea (Pisum sativum) chloroplast fragments. The Deriphat appears to have preserved at least to some extent a new type of chlorophyll a-protein complex.

Evidence that circularly dichroic chlorophyll forms a-682 and a-710 are oriented at right angles to the thylakoid membranes of whole chloroplasts, and that the circular dichroism is light-dependent

Chloroplasts from the pea (Pisum sativum L.) suspended in iso-osmotic buffered medium were oriented by flow in specially constructed cuvettes and examined for circular dichroism (c.d.). In one cuvette the flow was transverse to the direction of the light-path, but the other cuvette was designed so that flow and the light-path were coaxial. The induced orientation is such that the chloroplasts appear to move edgewise. C.d. was maximum when the light-path lay in the plane of the chloroplast disc. The intense c.d. of intact chloroplasts ascribed by Gregory & Raps [Biochem. J. (1974) 142, 193-201] to bulk chlorophyll a was found to contain two components, one the split-exciton type centred at 682nm and the other a simple maximum at 700-710 nm. The chlorophyll a-710 form was distinguished by its greater dependence on chloroplast orientation. The preferred direction of the transition moment in both chlorophyll forms was at right angles to the plane of the chloroplast, that is, at right angles to the plane of the thylakoids. This is in conflict with several reports based on polarization of fluorescence. It is suggested that the present effect is due to thylakoid-thylakoid interaction. Evidence for this is the reversible diminution in the c.d. signal caused by illumination in the presence of electron-transport reagents. It is argued that the c.d. is an indicator of chlorophyll movement, or changes in the thylakoid-thylakoid distance, possibly related to ion movement, affecting energy transfer between photosynthetic units.