Full-field dual modulation fluorescence lifetime imaging on rare earth ion upconversion

Fluorescence lifetime imaging microscopy (FLIM) is a powerful technique to map molecular environments independently of fluorophore density and excitation intensity. Despite its success, FLIM can be slow for long-lived and weak fluorescence. Here, we introduce full-field dual modulation FLIM (FDM-FLIM) for imaging weak and long-lived emitters. By modulating the excitation and emission and projecting the signal directly onto a camera, FDM-FLIM extracts lifetimes without frequency-domain phase retrieval. We demonstrate this for Er/Yb upconversion nanoparticles near plasmonic nanostructures, where Purcell-enhanced emission leads to spatially varying lifetimes that are otherwise obscured by nanoparticle-density variations, indicating that FDM-FLIM is a robust and accessible approach for full-field and hyperspectral lifetime imaging.