Multicolor cathodoluminescence imaging of single lanthanide nanoparticles.

Cathodoluminescence (CL) microscopy offers a promising approach to nanoscale analysis, enabling detection of optical emission from a sample while leveraging the high resolution of electron microscopy. However, achieving multicolor single-particle CL imaging remains a significant challenge. Here, using lanthanide nanoparticles as a model system, we identify a critical limitation in CL imaging: nonlocal signal caused by stray electrons. We mitigate these nonlocal excitations and demonstrate multicolor single-particle CL imaging of nanoparticles down to 12 nm in diameter. Using this enhanced sensitivity, we demonstrate that CL brightness increases monotonically with nanoparticle diameter. We propose that multicolor imaging of spectrally distinct nanoparticles in the same field of view, coupled with the scaling of CL brightness with nanoparticle size, is crucial for confirming single-particle CL detection. Finally, we demonstrate the utility of our findings by imaging lanthanide nanoparticles in a biological sample. This work advances our understanding of nanoscale photonic responses to free electrons, establishing CL as a useful contrast mechanism for high-resolution, multicolor electron microscopy.