Boris Kalinic

Implantation damage effects on the Er 3+ luminescence in silica

The possibility to control the room temperature Er3+ photoluminescence efficiency in silica is investigated in terms of the damage produced in Er-doped silica by implantations at different fluences with Xe or Au ions. These implantations are tailored to reproduce the same level of damage in Er-doped silica. The remarkable differences in terms of the photoluminescence intensity between Xe- and Au-irradiated samples allowed to decouple the detrimental effect of the implantation damage on the photoluminescence from the beneficial broad-band energy transfer process provided by molecule-like Au clusters formed upon thermal annealing. The evolution of the implantation damage is followed by photoluminescence and correlated to the local Er-site by x-ray absorption spectroscopy.

Optimal geometric parameters of ordered arrays of nanoprisms for enhanced sensitivity in localized plasmon based sensors

Plasmonic sensors based on ordered arrays of nanoprisms are optimized in terms of their geometric parameters like size, height, aspect ratio for Au, Ag or Au0.5-Ag0.5 alloy to be used in the visible or near IR spectral range. The two figures of merit used for the optimization are the bulk and the surface sensitivity: the first is important for optimizing the sensing to large volume analytes whereas the latter is more important when dealing with small bio-molecules immobilized in close proximity to the nanoparticle surface. A comparison is made between experimentally obtained nanoprisms arrays and simulated ones by using Finite Elements Methods (FEM) techniques.

Spectral dependence of nonlinear absorption in ordered silver metallic nanoprism arrays

Ordered metallic nanoprism arrays have been proposed as novel and versatile systems for the observation of nonlinear effects such as nonlinear absorption. The study of the effect of the local field reinforcement on the fast optical third order nonlinear response around the Surface Plasmon Resonance is of great interest for many plasmonic applications. In this work, silver nanoprism arrays have been synthesized by the nanosphere lithography method. A low repetition rate tunable picosecond laser source was used to study the irradiance and wavelength dependence of the nonlinear absorption properties around the dipolar and quadrupolar resonances of the nanoarray with the use of the z-scan technique. The irradiance dependence of the on-resonance nonlinearity was studied, and a spectral region where nonlinear absorption is negligible was identified. This is important for the possible application of these materials in optical information processing devices.

Dichroic nonlinear absorption response of silver nanoprism arrays

The properties of dichroism in the nonlinear absorption response of silver nanoprism arrays are experimentally investigated by the z-scan technique. Open aperture z-scan measurements are performed with a picosecond laser at a low repetition rate to excite the third-order electronic component of the optical nonlinearity for different linear polarization directions of the incident beam. A strong saturable absorber behavior is observed for all the linear polarization orientations and a continuous, sinusoidal modulation of the nonlinear absorption coefficient (up to about 30% of its absolute value) is demonstrated as a function of the polarization angle. The dichroic nonlinear absorption of the samples is explained by taking into account the polarization-dependent local electric-field distribution in the nanoprism arrays, as demonstrated by finite elements method electrodynamic simulations. These findings make silver nanoprism arrays an ideal platform for the development of nanophotonic devices with fast, strong and tunable nonlinear optical responses.

Energy-transfer from ultra-small Au nanoclusters to Er3+ ions: a short-range mechanism

Sub-nanometric Au nanoclusters are known to act as very efficient sensitizers for the luminescent emission of Er(3+) ions in silica through a non-resonant broad-band energy-transfer mechanism. In the present work the energy-transfer process is investigated in detail by room temperature photoluminescence characterization of Er and Au co-implanted silica systems in which a different degree of coupling between Er(3+) ions and Au nanoclusters is obtained. The results allow us to definitely demonstrate the short-range nature of the interaction in agreement with non-radiative energy-transfer mechanisms. Moreover, an upper limit to the interaction length is also set by the Au-Au intercluster semi-distance which is smaller than 2.4 nm in the present case.

Amplified sensitization of Er3+ luminescence in silica by AuN quantum clusters upon annealing in a reducing atmosphere

Finding effective strategies for improving the luminescence emission performance of Er3+ ions in silica is of paramount importance for the realization of efficient Er-based nanophotonic devices. To this aim, in the present work the sensitization mechanism of room temperature Er3+ luminescence by AuN quantum clusters, upon annealing in a reducing atmosphere, was investigated by photoluminescence characterization of Er–Au co-implanted samples in which Au ions were implanted at a low fluence of 3.4 × 1014 Au+ per cm2. The role of the annealing atmosphere was unveiled by comparing the emission properties of samples thermally treated in reducing and inert atmospheres. A significant amplification of the Er3+ sensitization efficiency (up to a 6× enhancement of the photoluminescent intensity) was revealed upon annealing in a reducing atmosphere and the possibility to get efficient room temperature Er3+ luminescence from Er–Au co-implanted samples with only a limited amount of sensitizing agents was demonstrated and discussed.

Rare-earth fluorescence thermometry of laser-induced plasmon heating in silver nanoparticles arrays

The laser-induced plasmon heating of an ordered array of silver nanoparticles, under continuous illumination with an Ar laser, was probed by rare-earth fluorescence thermometry. The rise in temperature in the samples was monitored by measuring the temperature-sensitive photoluminescent emission of a europium complex (EuTTA) embedded in PMMA thin-films, deposited onto the nanoparticles array. A maximum temperature increase of 19 °C was determined upon resonant illumination with the surface plasmon resonance of the nanoarray at the highest pump Ar laser power (173 mW). The experimental results were supported by finite elements method electrodynamic simulations, which provided also information on the temporal dynamics of the heating process. This method proved to be a facile and accurate approach to probe the actual temperature increase due to photo-induced plasmon heating in plasmonic nanosystems.

GaN-Based Laser Wireless Power Transfer System

The aim of this work is to present a potential application of gallium nitride-based optoelectronic devices. By using a laser diode and a photodetector, we designed and demonstrated a free-space compact and lightweight wireless power transfer system, whose efficiency is limited by the efficiency of the receiver. We analyzed the effect of the electrical load, temperature, partial absorption and optical excitation distribution on the efficiency, by identifying heating and band-filling as the most impactful processes. By comparing the final demonstrator with a commercial RF-based Qi system, we conclude that the efficiency is still low at close range, but is promising in medium to long range applications. Efficiency may not be a limiting factor, since this concept can enable entirely new possibilities and designs, especially relevant for space applications.

Wavelength- and polarization-dependent nonlinear optical properties of plasmonic nanoprism arrays

The nonlinear absorption properties of Ag nanoprism arrays synthesized by nanosphere lithography have been investigated by z-scan measurements. A picoseconds and low repetition rate laser source has been used to excite the electronic component of the nonlinear optical response without inducing thermal effects on the samples. Spectral effects in the nonlinear absorption response have been highlighted by performing measurements at different wavelengths, matching the laser wavelength with the dipolar and the quadrupolar surface plasmon resonances of the synthesized nanoarrays. The nonlinear absorption properties of the samples have been also investigated as a function of the polarization of the laser source and dichroism effects have been revealed.