Research axis 4

Multiphoton, upconversion in nanoparticles: Dr. M. Sliwa, Pr. H. Miyasaka

Lanthanide-doped inorganic nanoparticles present the unique feature of narrow emission bands up to the blue region of the visible spectrum when excited in the near infrared (NIR). Because biological samples show limited absorption in the NIR, the so-called Up-Converting NanoParticles (UCNPs) are attractive candidates for biological applications. In particular, since blue light can activate photochromic switches, the UCNPs, that are naturally not blinking, can blink when they are coupled to an organic molecular switch. Thus, the non-blinking emission of UCNPs (in the NIR range) can be used in a conventional way for nanoparticle tracking, whereas the blinking emission (in the visible range) will be used for super-resolution. The main issue is to understand the photo-dynamics of these new UCNPs. They are strongly dependent of the excitation power with the existence of multiphoton processes and energy transfer (energy hoping, one-photon and two photon absorption, singlet-singlet annihilation…). Rationalization of multiphotonic processes within UCNPs will lead to efficient control of the blinking dynamics. In general for all the axes a fine control of two-photon vs one-photon activation of the photochromic reactions will be important to get access to original photoactive devices. Preliminary results on photochromic quantum yield enhancement by multiphoton processes in organic nanoparticles have been already obtained through a collaboration between the ENS Paris Saclay group and Pr Miyasaka team in Osaka University, showing the advantages of synergetic photophysical behaviour in nanomaterials, compared to isolated molecules. So the main goal of this task is the rationalization of multiphotonic processes to understand cooperative processes within nanoparticles developed within this LIA. The Lille team is in charge of the NIR characterization of luminescent nanoparticles using its spectroscopic facilities, i.e. spatially super-resolved and time fluorescence techniques and advanced data analysis. In this task, the Pr. H. Miyasaka’s group (Osaka Univ.) will be in charge of multi-excitation time-resolved transient absorption spectroscopy and wide-field single molecule microscopy. In view of similar applications, the Japanese group of Pr. T. Kawai (NAIST) and J. Abe (Aoyama Gakuin Univ.) will be involved in the synthesis of NPs (UCNPs and organic NPs) with high two-photon absorption cross sections and photo-switching properties with multiphoton absorption.

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