Luminescent rare earth nanoparticles exhibit superior optical stability over commonly-used organic dyes and higher biocompatibility over quantum dots, rendering them advantageous as bioimaging nanoprobes. However, their typical excitation inhibits their broad employment with conventional fluorescence microscopes and, thus, solutions are sought to shift their activation in the long-wavelength (near-UV) spectral region. Here, we synthesize YVO4:Eu3+ nanophosphors by flame aerosol technology to systematically study the effect of Bi3+ codoping on their luminescence. That way, we identify an optimal Bi-content for sufficient near-UV activation. These nanophosphors are highly crystalline and appeared bright red under a conventional fluorescence microscope, facilitating bioimaging with HeLa cells and in vitro dosimetry correlations in the presence and absence of serum. The nanophosphor superiority over organic-dye-labeled silica nanoparticles is shown during dynamic imaging for 4 h without photobleaching for the former. These YVO4:Eu3+/Bi3+ nanophosphors can provide a non-photobleaching tool for further dynamic nanoparticle-cell interaction studies with conventional fluorescence microscopes. (C) 2018 American Institute of Chemical Engineers