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Advanced Spectroscopy of Functional Nanomaterials

Sergio Brovelli, Angelo Monguzzi, Francesco Meinardi

The team has a long standing tradition in the development of organic and organic/inorganic hybrid materials for applications in molecular photonics and electronics. More recently, our research activity has expanded to the study of fundamental and applied properties of colloidal semiconductor quantum dots and metal clusters that are emerging solution processable functional materials.

Specifically, our activity is focused on the following subjects:

 

Advanced Spectroscopy of colloidal Nanocrystals

Colloidal semiconductor nanocrystals (NCs) are solution-processable functional materials with growing applicative potential in strategic technological fields, such as light-emitting diodes, photovoltaic cells, lasers, luminescent markers and single photon sources. They feature high, near-unity emission efficiency, large absorption cross-sections and a tunable emission wavelength controlled by the NC size. Wavefunction engineering in NC heterostrustures and doping with transition metal ions provide additional degrees of freedom for controlling the optical and electrical properties of NCs. Our research is focused on fundamental and applied aspects of NC photophysics by means of ultrafast magneto-optics and spectroelectrochemical methods aimed at achieving advanced NC systems for application in solid-state light emitting sources, luminescent solar concentrators and NC solar cells.

 

Non Coherent Photon Up-conversion

The most recent advancements in photovoltaic and hydrogen photogeneration technologies require the adaptation of the solar spectrum to the device spectral response through photon management processes, rather than the tuning of the latter to match the solar spectrum. In this framework, conventional non-linear optics approaches are not applicable as they typically require excitation densities several orders of magnitude larger than the solar radiance. Our research is focused on the development of multicomponent organic systems that exploit annihilation processes of metastable states and thereby allow for the achievement of high up-conversion efficiencies at excitation densities as  low as a few μW/cm2. In our research we tackle both fundamental and applicative aspects aimed at the development of real-world devices. Our results have a significant impact both on photovoltaic technologies and on solid state lighting and imaging applications.

 

Luminescent solar concentrators (LSCs). Luminescent solar concentrators (LSCs) are cost-effective complements to semiconductor photovoltaic (PV) systems that can both boost the power output of standalone solar cells and allow for integration of PV-active architectural elements into buildings in the form of, for example, semi-transparent PV windows. A typical LSC consists of a plastic optical waveguide doped with fluorophores  or glass slabs coated with active layers of emissive materials. Sunlight, which penetrates the matrix, is absorbed by the fluorophores and then re-emitted at a longer wavelength. The luminescence, guided by total internal reflection, propagates towards a PV cell placed at the edge of the waveguide where it is converted into electricity. Our research team has a dedicated effort for the development of new emitters for efficient large-area LSC devices that require fluorophores with near unity emission efficiencies, broad coverage of the solar spectrum and minimized overlap between the absorption and emission spectra, so as to suppress the optical losses by re-absorption. Furthermore, an important aspect of our research is focused on advanced strategies for the incorporation of emitters into polymeric matrixes for producing polymeric nanocomposites that preserve the optical features of the fluorophore intact.

 

Facilities

Our research team has a variety of state-of-the-art facilities for the spectroscopic investigation a variety of nanomaterials as well as for the synthesis and manipulation of functional nanostructures.

Among the set-ups present in our labs, we dispose of a 5 Tesla cryo-magnet for magneto-optical studies at temperature down to 1.5 K, an ultrafast time-resolved photoluminescence line with resolution of a few ps, confocal microscope for single molecule/particle spectroscopy, a transient absorption setup for photoinduced absorption measurements in the ns time regime.

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