In this work ZnO thin films were deposited on different substrates, glass, silicon (100), and MgO (100) using rf‐magnetron sputtering at low temperature in order to promote a large defect density, aiming to study a possible correlation with the observed violet/blue emission band. The peak position, width and low energy band shape asymmetry of the violet/blue band was found to be dependent on the deposition temperature and oxygen partial pressure. The structural analysis of deposited films reveals an epitaxial relationship for the a ‐oriented ZnO/MgO while for the c ‐oriented ZnO/Si no epitaxial relation was found with the substrate. The dependence of the violet/blue band on temperature displays always a shift of the peak position to lower energies, discarding the hypothesis of a free to bound transition. The sublinear dependence of the emission intensity with the excitation intensity suggests that the violet/blue bands on both samples could have a donor‐acceptor pair nature. However, the unusually strong shift of the peak position to lower energies for the ZnO/MgO films and the emphasised asymmetric band shape for the ZnO/Si samples suggest that potential fluctuations in the electronic bands, due to disorder induced charged defects, could also be considered as an alternative recombination model for the violet/blue band. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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The magnetic behavior of bulk La2/3Ca1/3MnO3 (TC=267 K) at low fields in the paramagnetic phase was studied. Near TC(T−TC<30 K) we find a sequence of steplike features in the effective Curie constant C(T)=M(T−TC)/H at well defined temperatures and intermediate plateaus, accompanied by temperature hysteresis. On approaching TC, the C values at each plateau follow a geometrical progression, with the effective spin S doubled at each step. The first plateau gives S=5.5, corresponding to a cluster of three Mn3+ ions sharing one extra hole. This suggests that close to TC short range magnetic order at low fields develops hierarchically through a series of most stable cluster states.

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