Synthesis, Cytotoxicity Assessment and Optical Properties Characterization of Colloidal GdPO(4):Mn(2+), Eu(3+) for High Sensitivity Luminescent Nanothermometers Operating in the Physiological Temperature Range

Herein, a novel synthesis method of colloidal GdPO(4):Mn(2+),Eu(3+) nanoparticles for luminescent nanothermometry is proposed. XRD, TEM, DLS, and zeta potential measurements confirmed the crystallographic purity and reproducible morphology of the obtained nanoparticles. The spectroscopic properties of GdPO(4):Mn(2+),Eu(3+) with different amounts of Mn(2+) and Eu(3+) were analyzed in a physiological temperature range. It was found that GdPO(4):1%Eu(3+),10%Mn(2+) nanoparticles revealed extraordinary performance for noncontact temperature sensing with relative sensitivity S(R) = 8.88%/°C at 32 °C. Furthermore, the biocompatibility and safety of GdPO(4):15%Mn(2+),1%Eu(3+) was confirmed by cytotoxicity studies. These results indicated that colloidal GdPO(4) doped with Mn(2+) and Eu(3+) is a very promising candidate as a luminescent nanothermometer for in vitro applications.