The effect of carbonate impurities in the photoluminescence (PL) properties of hydroxyapatite has been studied. Different hydroxyapatite samples were synthesized by chemical precipitation with some differences in the purity of the precursors or the final neutralization treatment. All the materials were calcined in the temperature range of 200–800 °C. Calcination treatments in the range of 400–450 °C resulted in intense and broad luminescence spectra. Especially high PL intensity was obtained in samples HaB which was neutralized with phosphoric acid and in HaD a carbonated apatite. The band gap of these samples was in the range of 3.1–3.96 eV. The materials were characterized by Fourier Transformed Infrared spectroscopy, scanning and transmission electron microscopy, differential scanning calorimetry and x-ray diffraction. The time resolved luminescence decay was in the range from 500 to 980 ms in samples HaB, for calcination temperatures from 400 to 500 °C. The PL properties of these non-toxic materials made them very promising for new optical applications.

Lanthanide-based optical nanothermometers, operating in the physiological temperature range (288–323 K), with excitation and emission in the first biological transparent window have special interest for biological applications. In this context, trivalent europium doped titanium oxide (Eu3þ:TiO2) nanoparticles were prepared via a sol-gel method and their spectroscopic properties were studied. In order to assess their potential for temperature sensing, excitation and luminescence spectroscopies were performed. We observed that the intensities of the excitation bands for the 7F0→5D0 (576 nm) and 7F2→5D0 (610 nm) transitions, monitoring the 5D0→7F4 (700nm) transition have a strong dependence on temperature. This dependence, which is explained in terms of a thermal coupling between the Eu3þ:7FJ levels, was used for the construction of an optical nanothermometer. Relative sensitivity values between 1.78 and 1.41% K? 1, when the temperature of the material increases from 288 to 323 K, were obtained. We show that the nanothermometer calibration can be obtained by a single luminescence room temperature measurement. Our results indicate the potential application of Eu3þ:TiO2 nanoparticles for temperature sensing in the first biological window and physiological temperature range.