Lanthanide‐Doped NaGdF ₄ Nanoparticles as Versatile Luminescent Labels for Cathodoluminescence Mapping

A water‐based synthesis for lanthanide‐doped NaGdF 4 nanoparticles is presented, yielding nanoparticles that emit robust and efficient luminescence when excited with an electron beam (cathodoluminescence). Scanning electron microscopy reveals that the as‐fabricated nanoparticles exhibit a spherical shape with diameters ranging from 100–200 nm, accompanied by a granular surface structure. Powder X‐ray diffraction confirms that the as‐prepared product particles are highly crystalline and possess a hexagonal‐phase pure structure with average crystal sizes of ≈5 nm for the (100) plane. The presence of sodium, gadolinium, fluorine, and europium/terbium dopants has been verified by energy dispersive X‐ray spectroscopy. The elemental ratios demonstrate a high degree of similarity to the stoichiometric ratios of the initial precursor solutions. Incorporating europium or thulium dopants leads to distinctive spectral characteristics in the cathodoluminescence spectra, manifesting in red or blue spectral emission lines, respectively. From a mixture of the differently doped nanoparticles, the type of doping could be clearly identified for individual particles, and sufficient stability is proven to enable multiple consecutive measurements. As the synthesized nanoparticles are moreover hydrophilic and compatible with aqueous media, they offer high promise for cathodoluminescence mapping of organic or biological samples, enabling precise labeling with distinct and stable spectral signatures.