Sub-50-ns ultrafast upconversion luminescence of a rare-earth-doped nanoparticle

A tilted plasmonic nanocavity enables shortening of the luminescence decay time of a rare-earth-doped nanoparticle to sub-50 ns. High quantum efficiency enhancement, chiral polarization and directional far-field emission are maintained. Rare-earth-doped upconversion nanoparticles are attracting considerable attention because of their stable, coherent, narrowband and multi-colour luminescence, which features less dephasing effects, crosstalk, photo-blinking and photo-bleaching compared with quantum dots and organic dyes. However, due to the 4f-4f forbidden transitions of rare-earth ions, upconversion nanoparticles exhibit long luminescence decay times, ranging from microseconds to milliseconds, restricting their application in time-dependent nanophotonic devices. Here we fabricate a tilted plasmonic nanocavity to shorten the luminescence decay time of a rare-earth-doped nanoparticle to sub-50 ns while maintaining high quantum efficiency enhancement, tunable polarization-dependent and far-field directional emissions and selective polychromatic chirality. We expect this new type of ultrafast, directional and polarized luminescence of a rare-earth-doped nanoparticle to vigorously promote the development of coherent single-photon sources, quantum communications and nanolasers.