Production and characterization of nanostructured materials for optical aplications at Rovira i Virgili University

Abstract

Novel physical properties arise when the size of well-established optical materials is decreased to the nanometer range. This has generated great interest in all aspects of the synthesis and characterization of such nanocrystals, from materials for laser applications to materials for frequency conversion phenomena. In this paper we present three new approaches for studying these materials. Nanocrystals of laser materials are expected to show new spectroscopic features compared to their bulk counterparts. This has led to advances in the procedures for the synthesis of nanocrystals of double potassium tungstates and lutetium sesquioxides, both containing lanthanide ions, using a sol-gel approach: the Pechini method. We extensively characterize the structure and spectra of these new nanocrystals with the aim of facilitating the production of new ceramic materials with laser applications. We also analyze the morphology and vibrational structures of the nanoparticles produced. We synthesized also Er-doped GaN sub-micron-sized rods on silicon (001) through the direct reaction of gallium and ammonia in a simple chemical vapor deposition system. This allowed us to study the unique properties that natural electron confinement leads to in such widebandgap semiconductors. We studied their spectroscopic properties in depth to understand the excitation mechanisms of lanthanide ions in such semiconductor structures, which can lead to nearly ideal optical emissions. We recorded green and red emissions at room temperature coming from submicron- sized rods with excitation below the energy of the bandgap. Finally, the formation of ordered arrays of these one-dimensional structures is of special interest due to the new properties that may arise when compared to individual one-dimensional structures. At the Física i Cristal·lografia de Materials laboratory at Universitat Rovira i Virgili (URV) we produced two-dimensional photonic crystals of KTiOPO4, a non-linear optical material, using an entirely new procedure that combines bottom-up and top-down approaches. We produced an ordered array of KTiOPO4 one-dimensional structures using a silicon macroporous template and a KTi- OPO4 substrate to control their orientation. We demonstrated the physical properties of these photonic crystals: we measdiured their third-order forbidden band, and explored their near-IR and visible light diffraction properties.