Abstracts

Optical and photonic systems are nowadays at the heart of modern technology towards sustainable and energy-efficient devices for computing, communication, data security, including photonic integrated circuits and the newly emerging frontier of quantum optics. The high color pure and long lived emission delivered by the lanthanide f-f transitions establishes a unique value for the realization of such devices, which require efficient near-infrared (NIR) optical output (1 μm to 2 μm), to match with the silicon window in photonic integrated circuits and silica in telecom optical fibers. Nonetheless, recently, wavelength tunability allowing for signal multiplexing is becoming a much sought-after property to expand the potentialities of these technologies.Nanomaterials doped with lanthanide ions (Ln) offer countless possibilities for tailoring the optical output towards the desired functionality and at the same time deliver high processing potential by mild solution methods for the fabrication of optical devices. However, the emission intensity achievable in such materials remains low due to the poor absorption of these ions resulting in an inefficient photosensitization. For this reason, dye-sensitized lanthanide fluoride nanoparticles, where photosensitization is achieved through an organic light-harvesting unit, have become increasingly popular in the last years. On the other hand, the energy transfer at the organic-inorganic interface and the energy propagation within the nanoparticle is severely subjected to losses due to the presence of external and uncontrolled channels for the deactivation of the photoexcited states resulting in a dramatic lowering of the quantum yield. Ultra-fast transient absorption (TA) spectroscopy combined with time-resolved photoluminescence (PL) reveals the mechanisms and the short-lived intermediates at the organic-inorganic and Ln-Ln interfaces in dye-sensitized Ln³⁺-doped fluoride nanoparticles. By adopting a “molecule on a particle approach” where the energy donor and acceptor units are spatially confined into a precise core-shell architectural design of the nanoparticle and by selecting suitable small-sized (sub nm) dye molecules, it is possible to achieve exceptional sensitization efficiencies close to 100%.More recently, Ln-doped lead halide perovskite nanoparticles are also emerging as alternative materials to achieve highly efficient emission. In such systems, the large absorption cross section (10^-14 – 10^-13 cm²) of the perovskites for light with a photon energy above the LHP band gap, greatly facilitates the harvesting of the energy needed to excite the dopant ions. Perovskite materials offer enhanced absorption cross sections, high excitation densities and semiconducting properties. Extremely high quantum yield, exceeding 100% at ~1 µm, can be reached in Yb³⁺ doped CsPbCl₃ nanocrystals which in turn can be exploited to achieve outstanding intense and long lived emission from Er³⁺ at 1.5 μm, creating novel perspectives for developing Ln-based optical devices operating in the near-infrared window.