Numerical analyses of the ultraviolet and visible plasmonic spectra measured from hemispherical gallium nanostructures on dielectric substrates reveal that resonance frequencies are quite sensitive to illumination angle and polarization in a way that depends on nanostructure size, shape, and substrate. Large, polarization-dependent splittings arise from the broken symmetry of hemispherical gallium nanoparticles on sapphire substrates, inducing strong interactions with the substrate that depend sensitively on the angle of illumination and the nanoparticle diameter.

This work is aimed at gaining a better insight into the influence of a close vacancy, V, on the properties of impurities in insulating materials. To achieve this goal the Cr 3+ − V M model center formed in KMF 3 (M = Mg, Zn) fluoroperovskites has been explored in detail by means of ab initio calculations on clusters involving up to 87 ions. It is shown that the presence of the M 2+ vacancy, V M , induces a significant structural relaxation on the CrF 3− 6 cubic complex which cannot be fully understood assuming that ions were rigid spheres that could not be polarized. Thus, although V M forces all the ligands to move away, the Cr 3+ − F − distance corresponding to the furthest ligand, F far , is found to be slightly higher than that for the closer equatorial ions. This unexpected fact is shown to be due to the electronic relaxation also induced by V M on the CrF 3− 6 complex, causing a charge of 0.2e to be transferred from the closest ligand to V M , F next , mainly to F far , and, to a lesser extent, to any equatorial ligand. This transfer of charge is mainly accomplished through orbitals lying in planes containing the C 4 axis. In spite of these changes due to the vacancy, the 4 A 2g → 4 T 2g optical transition is found to be weakly altered, a fact that concurs with available experimental data and whose origin is discussed. In contrast, electron paramagnetic resonance parameters such as gyromagnetic or superhyperfine tensors, which do depend on the electronic density around a point of the CrF 3− 6 complex, are shown to be particularly sensitive to the electronic relaxation induced by V M . In particular, the present study explains that the dominant component of the superhyperfine tensor for the F next ligand is clearly higher than that for F far , in agreement with experimental data. The relevance of the present results for understanding the electronic properties of other systems involving vacancies is also discussed. Some results on the Cr 3+ − Li + center formed in KMgF 3 are also discussed for comparison.

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