Seminarium Optyczne

Lanthanide ions doped inorganic nanoparticles (LnNP) are potential candidates and alternative labels to fluorescent molecules and quantum dots. Among the other, they display narrowband absorption and emission lines, multicolour emission, long luminescence lifetimes and are perfectly photostable. In sensitized configuration, they are also capable to efficiently convert NIR excitation to visible range (so called upconversion UC), thus avoiding background fluorescence and enhance signal to background ratio towards super-sensitive biosensing & imaging. They also display non-linearity of luminescence intensity versus pump intensity, which enables imaging beyond diffraction limit with simple, customized confocal setups.Among upconversion processes leading to the anti-Stokes emission, the photon avalanche (PA) became an interesting research topic since 1979, when it was first observed in Pr3+ doped LaCl3 [1]. There are several essential requirements necessary to enable observation of PA in a given system – these include (i) the presence of efficient ESA transition and negligible GSA at the pumping wavelength and (ii) the presence of efficient the cross-relaxation (CR) processes required to populate intermediate excited level. As a consequence, the luminescence intensity of PA increases by several, typically 2-3 orders of magnitude when exciting with power density slightly (e.g. twice) above the PA threshold. Only recently its PA emission was also demonstrated for NaYF4 nanoparticles doped with Tm3+ at the room temperature under 1064 and 1450 nm photoexcitation and 800 nm emission [3].In this lecture, current state-of-the-art on PA emission and the PA emission in nano, micro and bulk LiYF4 crystals will be summarized. Moreover, peculiarities of photon avalanche emission in wider context as the paradigm shift in luminescent nano-bio-labels will be discussed. The wide application potential of PA (e.g. super-resolution imaging [3], biosensing [4], nano-thermometry [5] etc.) makes it extremely interesting to further studies of the PA in various lanthanides and various matrices of various sizes – these applications will be evaluated and future directions & challenges will be emphasized for materialscientists. References: [1] J. S. Chivian, W. E. Case, and D. D. Eden, Appl. Phys. Lett. (1979) 35, 124–125.; [2] M. F. Joubert, Opt. Mater. (Amst). (1999) 11, 181–203.; [3] Ch. Lee et al., Nature (2021), 589, 230-235; A.Bednarkiewicz et al. (2019) Nanoscale Horizons, 4(3), 706-719; [4] A.Bednarkiewicz, E.Chan, K.Prorok, Nanoscale Adv., 2020,2, 4863-4872; [5] M.Szalkowski et