Photoinduced dichroism in various polymers containing the same azo dye has been studied. "Angular hole burning" and molecular reorientation have been identified by analysis of dichroism dynamics at various probe wavelengths. The glass-transition temperature T(g) is of major relevance for the reorientation of optically active molecules. For low T(g) (below ambient temperature) thermal diffusion impedes anisotropy buildup. For higher T(g) the angular distribution induced by the polarized pump beam is frozen. We propose a simple model based on diffusion rates in trans and cis molecules.
Observations with the French (L.P.S.P.) experiment on board OSO-8 of a sunspot and nearby plage region are described. The behaviour of the emission cores of the Ca II H and K and Mg II h and k resonance lines is very similar and the correspondence in intensity between the four lines persists in all observed features. In contrast, the Lyman lines show little correlation with the other lines. Their emission regions appear broader in the spectroheliograms than the underlying sunspot structure and must not necessarily possess a counterpart in lower layers. From the central intensity of La above the umbra an
The electrical and photoconductive properties of Bridgman grown vanadium-zinc co-doped CdTe bulk crystals are strongly influenced by one native intrinsic defect previously attributed to the Te vacancy. In order to identify this defect and control its formation mechanism, a correlated electron paramagnetic resonance (EPR) and modulated photocurrent (MPC) study has been made. The results obtained allow us to attribute this defect to the Te Cd antisite, a double donor. By EPR and MPC its +/2+ level position has been determined to E c − 0.20 eV. Four other centres of minor concentrations were characterized by MPC in as-grown crystals. From the MPC results the density of states for CdTe:V materials has been determined.
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