Hybrid nanostructures containing neodymium-doped nanoparticles and infrared-emitting quantum dots constitute highly sensitive luminescent thermometers operating in the second biological window. They demonstrate that accurate subtissue fluorescence thermal sensing is possible.

In this work, the synthesis and photoluminescence response of HfO 2 doped with Eu 3+ (HfO 2 :Eu 3+) are reported. The synthesis was carried out by the hydrothermal route of HfCl 4 and EuCl 3 ·6H 2 O with NH 4 OH dissolved in deionized water. To perform the hydrolysis, the precursors were subjected to hydrothermal treatment at 120˚C, under autogenously pressure at reaction times of 24, 40, 52 and 72 hours. The synthesized nanoparticles were characterized by mean of Xray diffraction (XRD), high resolution transmission electron microscope (HRTEM), and energy dispersive spectroscopy (EDS). Samples excited with 395 nm radiation show photoluminescence emission lines corresponding to the electronic transitions 5 D 0 → 7 F J (J = 0→4), characteristics of the Eu 3+ ion. The photoluminescence emission intensity increases with the increasing of the reaction time, reaching a maximum at 72 hours. The excitation band peaked at 395 nm, makes this material an excellent candidate for applications in solid state white lamps.