Synthesis and spectroscopic properties of monocyclic and bicyclic erbium phtalocyanines

Bimacrocyclic and monomacrocyclic erbium phtalocyanines have been synthesized and their luminescence spectra and lifetimes have been studied. The bi-planar structure of ErPc₂ complexes, although interesting at first sight, is non-luminescent because of a strong absorption band near 1.5 μm. However, the luminescence of the erbium ion can be recovered after oxidation or reduction of the macrocycle. Monomacrocyclic erbium phtalocyanines exhibit a strong luminescence of erbium as a result of the energy transfer between the excited phtalocyanine macrocycle and the erbium ion. With a perchlorinated phtalocyanine and a perdeuterated axial ligand in a deuterated solvent, the luminescence lifetime reaches 5 μs, which is the maximum lifetime found for conventional perdeutarated ligands. The large absorption cross-section of phtalocyanine in the red may counterbalance the fast luminescence lifetime, allowing the hope for a new all-organic integrated optical amplifier device.     

On column generation formulations for the RWA problem

We present a review of several column generation formulations for the Routing and Wavelength Assignment (rwa) problem with the objective of minimizing the blocking rate. Several improvements are proposed, together with a comparison of the different formulations with respect to the quality of their continuous relaxation bounds and their computing solution ease. Experimental results are presented on several classical network and traffic instances.     

Distribution of the strength of acid sites in mildly steamed HZSM-5 studied by IR spectroscopy

Steaming resulted in modification of the distribution of acid strength of OH groups. The contribution of less acidic sites increased and new, very strongly acidic hydroxyls characterized by IR band at 3590 cm^-1 appeared.     

AgInS2–ZnS nanocrystals: Evidence of bistable states using light‐induced electron paramagnetic resonance and photoluminescence

The precursor (AgIn)_x Zn_2(1–x)(S₂CN(C₂H₅)₂)₄ was used to prepared AgInS₂–ZnS nanocrystals with different compositions (x = 0.4 and x = 0.7) and with different time of reaction (10 min and 75 min). The photoluminescence features of the nanocrystals were addressed by combining steady‐state spectroscopy and light‐induced electron paramagnetic resonance. Both techniques showed the contribution of at least two components for the emission, previously assigned to surface and intrinsic states. Light‐induced electron paramagnetic resonance allowed detection of the photocreation both of irreversible paramagnetic species that are likely responsible for the nano‐crystals degradation assigned to surface states and of reversible paramagnetic species assigned to intrinsic states. Moreover, reversible bistable paramagnetic states were observed. This Letter provides a scheme that might be useful in addressing the well‐known problem of aging of the nanocrystals. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)