Photoluminescence, cytotoxicity and in vitro imaging of hexagonal terbium phosphate nanoparticles doped with europium

Luminescent TbPO₄ nanoparticles were synthesized via a citric-acid-mediated hydrothermal route. Eu³⁺ doping of TbPO ₄ enables an efficient Tb³⁺-to-Eu³⁺ energy transfer, leading to a four-fold increase of the absolute emission quantum yield (QY), compared to that of undoped TbPO₄. To check the potential of biological use, we conducted in vitro biological experiments on human cervical carcinoma HeLa cells incubated with TbPO₄:Eu nanoparticles. TbPO ₄:Eu nanoparticles can be successfully internalized into the cells, and they show bright intracellular luminescence and very low cytotoxicity. Photoluminescence intensity dependence upon time demonstrates that Eu ³⁺-doped TbPO₄ nanoparticles are highly resistant to photobleaching. Our present work represents a demonstration of the use of rare-earth-based nanocrystals as a biological labeling agent because they combine several advantages including high emission quantum yield, long luminescence lifetime, low cytotoxicity and high photostability.