This work introduces non-covalent hydrophilic coating of NaGd0.7Eu0.3F4 nanocrystals by polylysine (PL) and polyethyleneimine (PEI) for MRI and fluorescent imaging purposes. PL- and PEI-stabilized nanocrystals exhibit high colloidal stability, cell internalization, fluorescent contrasting of nuclei and cytoplasm, low cytotoxicity, and relaxivity (r1= 0.17 dm3 mmol–1 s–1 and r1 = 0.23 dm3 mmol–1 s–1). © 2024