Although the optical and plasmonic properties of noble metal (Ag and Au) nanoparticles (NPs) have been thoroughly studied and reported, less information is available concerning NPs made of non-noble metals or semimetals that present a more complex electronic structure. In this work, we combine experiments and modeling to explore the optical response of bismuth NPs in the near-ultraviolet, visible, and near-infrared, which has not been studied so far, despite the unusual and interesting electronic properties of bulk Bi. Two dimensional distributions of Bi NPs with different topologies have been prepared and embedded in a protecting and transparent dielectric matrix, thus providing robust materials suitable for structural and optical characterizations. The Bi NP distributions display optical resonances whose spectral position and width are topologysensitive. The observed macroscopic optical response has been modeled by quasistatic effective medium models, and the analysis shows that the optical resonances present features similar to those of surface plasmon resonances, such as environmental sensitivity. In contrast to noble metals resonances, important nonradiative damping is evidenced in the whole near-ultraviolet-tonear-infrared range, likely due to interband desexcitation paths available in Bi in relation to its electronic structure. Finally, dynamic calculations of the optical extinction performed as a function of the NP's size and shape show a roadmap for tuning the spectral position of the optical resonances in Bi NPs in the whole near-ultraviolet, visible, and near-infrared range.

Erbium doped Al 2 O 3 films with concentrations up to 6ϫ10 20 Er cm Ϫ3 have been prepared in a single step process by pulsed-laser deposition. Alternate ablation of Al 2 O 3 and Er targets has been used to control the in-depth distribution and in-plane concentration of Er 3ϩ ions independently. The characteristic Er 3ϩ photoluminescence response at 1.53 m has been studied as a function of the Er 3ϩ distribution. It is found that lifetime values can be greatly increased by increasing the Er 3ϩ-Er 3ϩ in-depth separation above 3 nm. This result can be related to a reduced Er 3ϩ-Er 3ϩ energy migration process. The in-plane Er 3ϩ concentration was increased by either increasing the number of pulses on the Er target or the laser energy density for ablation. By the latter method in-plane concentrations as high as 1.1ϫ10 14 Er cm Ϫ2 per layer ͑corresponding to 2 ϫ10 20 Er cm Ϫ3 ͒ were achieved, while keeping lifetime values as high as 6 ms. This result is explained in terms of shallow Er 3ϩ implantation during deposition.

V centers induced by ionizing irradiation at 80 or 300 K in single-crystal and polycrystalline MgA1204 samples have been studied by use of electron paramagnetic resonance and optical absorption. V, and V, centers, as a result of hole trapping at tetrahedral and octahedral cation vacancies, respectively, have been found to be responsible for two EPR bands centered at g =2.011 and optical absorption bands involved in the complex absorption spectrum at about 3.4 eV. These centers anneal thermally in a very wide step from 220 to 575 K.

Erbium-doped Al 2 O 3 films have been deposited in a single step process by pulsed laser deposition using independent ablation of Al 2 O 3 and Er targets. This procedure allows to control the Er 3ϩ ions in-depth distribution. The characteristic Er 3ϩ photoluminescence at 1.54 m shows lifetime values which increase from 6.0 to 7.1 ms when the Er 3ϩ-Er 3ϩ in-depth separation is increased from 3 to 9 nm. These results are discussed in terms of the ion-ion interaction and clustering for separations shorter than 6 nm.

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