Lucía Labrador-Páez

Unveiling Molecular Changes in Water by Small Luminescent Nanoparticles.

Nowadays a large variety of applications are based on solid nanoparticles dispersed in liquids-so called nanofluids. The interaction between the fluid and the nanoparticles plays a decisive role in the physical properties of the nanofluid. A novel approach based on the nonradiative energy transfer between two small luminescent nanocrystals (GdVO4 :Nd3+ and GdVO4 :Yb3+ ) dispersed in water is used in this work to investigate how temperature affects both the processes of interaction between nanoparticles and the effect of the fluid on the nanoparticles. From a systematic analysis of the effect of temperature on the GdVO4 :Nd3+ → GdVO4 :Yb3+ interparticle energy transfer, it can be concluded that a dramatic increase in the energy transfer efficiency occurs for temperatures above 45 °C. This change is properly explained by taking into account a crossover existing in diverse water properties that occurs at about this temperature. The obtained results allow elucidation on the molecular arrangement of water molecules below and above this crossover temperature. In addition, it is observed that an energy transfer process is produced as a result of interparticle collisions that induce irreversible ion exchange between the interacting nanoparticles.

Optical trapping for biosensing: materials and applications

Since the 70s, when Arthur Ashkin and coworkers demonstrated that optical forces could displace and levitate microsized particles, optical trapping has seen a steady stream of developments and applications, particularly in the biological field. Since that demonstration, optical trapping has been especially exploited as a powerful tool for non-invasive sensitive measurements. The recent development of synthesis routes has further expanded the possibilities of optical trapping in the area of biosensing where new multifunctional particles are used as a single probe. The synergy between the development of new materials and experimental techniques has led to the appearance of numerous studies in which novel biosensing applications are demonstrated. The design of new materials and optical systems to face new challenges makes it necessary to have a clear idea about the latest developments achieved in the field. In this work, we summarize recent experimental advances in biosensing achieved by optical manipulation of micro- and nanoparticles providing a critical review on the state of the art and future prospects.

Depressed-Cladding 3-D Waveguide Arrays Fabricated With Femtosecond Laser Pulses

We report on the fabrication of waveguide arrays based on depressed-cladding structures produced by femtosecond laser direct inscription in a Nd:YAG crystal. The arrays consisted of seven divergent hexagonal waveguides with different separations between the waveguides at the exit of the crystal. Optical characterization in the visible (633 nm) and near infrared (800 nm) was performed. The obtained modal profiles show multimodal behavior in the visible and nearly single-mode at 800 nm. The propagation losses were measured to be 1.6–3.0 dB/cm in all the cases. Microluminescence maps were obtained showing the presence of defects only at the damage tracks and a residual stress that slightly affects the waveguide core in the vicinity of the tracks. This affected area is responsible for a modal profile distortion that can be clearly seen at 633 nm, but does not modify the modal profiles in the near infrared. Our results show a very good performance of the fabricated structures and suggest a promising potential use in photonic applications (i.e., photonic lanterns) that can be easily implemented in other transparent materials.