Seminarium Optyczne

Upconverting nanoparticles (UCNPs) doped with lanthanide ions convert near-infrared radiation into visible emission through sequential absorption processes involving long-lived electronic states. While the basic mechanisms of upconversion have been extensively studied, recent experiments reveal that UCNPs can exhibit a number of less intuitive photophysical behaviors. In this seminar, I will discuss several examples of such phenomena. First, I will focus on the strong enhancement of upconverted emission under dual-wavelength near-infrared co-excitation, where simultaneous excitation of ground-state and excited-state transitions leads to emission intensities far exceeding those obtained under single-wavelength excitation. I will also briefly discuss collective emission phenomena, including upconversion superfluorescence, in which ensembles of emitters synchronize to produce intense, ultrafast bursts of radiation. These examples illustrate how the rich energy-level structure and long lifetimes of lanthanide ions give rise to unconventional optical dynamics, opening new directions for nanophotonics, sensing, and imaging technologies.