The strong interest in solar energy motivates the scientific community to improve the energy conversion efficiency of solar panels (SPs). Indeed, the implementation of plasmonic nanoparticles (NPs) in SPs can enhance the absorption coefficient due to the well-known localized surface plasmons resonances (LSPR) and then increase SP efficiency. However, the silicon-based SPs do not absorb the solar radiation above 1000 nm wavelengths. One of the solutions is to use an enhancement of up-conversion photoluminescence (PL) coupled with a plasmonic NP . Shortly, a fluorophore absorbing several photons simultaneously in the IR exhibits emission in the range of the silicon absorption band and this process can be enhanced by plasmonics.
Recently, it has been shown that 170 nm-diameter single gold nanocylinders (GNCs) have multi-resonant characteristics . In this work, we report on the simultaneous excitation and emission enhancements of quantum dots up-conversion PL (two-photon photoluminescence (TPPL)) assisted by dipolar and quadrupolar modes of a single GNC.
Indeed, the use of radial and linear polarizations allows us to obtain singly or doubly enhanced TPPL respectively. We show that double resonantly enhanced up-conversion can be higher by 4-7 times than single resonant up-conversion.
 J.G. Smith, J.A. Faucheaux, P. K. Jain, "Plasmon resonances for solar energy harvesting: A mechanistic outlook," Nano Today, 10, 67-80 (2015).
 A. Movsesyan, A.-L. Baudrion, P.-M. Adam, "Revealing the hidden modes of a gold nanocylinder, " Journal of Phys. Chem. C, 122(41), 23651-23658 (2018).
Plasmonic oligomers allow new ways to manipulate nonlinear optical effects such as second-harmonic generation (SHG) through collective resonances. However, earlier techniques to probe such effects have relied mostly on the use of plane waves or focused beam excitations with homogenous states-of-polarization (e.g., linear) that obviously do not match the spatial symmetries of the oligomer. Here, we investigate collective effects in the SHG from individual plasmonic oligomers using microscopy with cylindrical vector beams such as radial or azimuthal polarizations. The oligomers were prepared by electron-beam lithography. The oligomers consisted of gold nanorods that have a longitudinal plasmon resonance close to the fundamental wavelength that is used for SHG excitation and whose long axes are arranged locally such that they follow the distribution of the transverse component of the electric field of radial or azimuthal polarizations. We found that SHG from such oligomers is strongly modified by the interplay between the properties of the incident cylindrical vector beam and interparticle coupling. We find that the oligomers with radially-oriented nanorods exhibit small coupling effects. In contrast, we observed that the oligomers with azimuthally-oriented nanorods exhibit large coupling effects that lead to silencing of SHG from the whole structure. We found good qualitative agreement between our experimental findings and calculations using the method of moments. The work describes a new route to investigate coupling effects in arrangements of nanostructures and thereby to control the efficiency of nonlinear effects in these structures.
Individual small gold structures of different sizes and shapes are fabricated on planar substrates for subsequent
characterization of their optical properties. In the process, a combination of thin-film metallization, electron beam
lithography and ion milling is employed, where electron beam structured hydrogen silsesquioxane is used as an etch
mask for the underlying gold layer. Gold cones, vertical rods, cups and flat disks can be prepared with a typical height of
about 100 nm. Their optical properties are investigated by confocal optical microscopy using a parabolic mirror for both
laser focusing and signal collection. As an example, the photoluminescence signal collected from an array of gold cones