Organic Acid-driven Synthesis of Photoluminescent Hydroxyapatite Nanoparticles Hybridized with Carbon Compounds: A Novel Approach to Emission Color Control

We successfully synthesized photoluminescent carbon compounds (CC) hybridized Eu3+ and F− ions co-doped hydroxyapatite nanoparticles, and evaluated the photoabsorption and photoluminescence (PL) properties of the nanoparticles with the thermal treatment. Specifically, the intermolecular dehydration occurred between citric acid (Cit) molecules as well as between Cit and L-Cysteine to effectively form the luminescent CC which showed blue-color-emitting by the thermal treatment at 85–140°C. By the thermal treatment at 140°C, the nanoparticles exhibited the wider PL emission color range with the higher internal quantum yield (15.3%) in the combination with Eu3+ ions which showed the red-color-emitting. With the thermal treatment at 140–180°C, the carbonization rate of CC increased and then the luminescent CC was changed into the non-luminescent graphene-like CC, which led the increase in the absorption efficiency, resulting in the purple to pink-color-emitting nanoparticles. From the above, it is possible to control the carbonization rate and the state of CC by the thermal treatment temperature, and realize the nanoparticles with the wider PL emission color range, which is expected to be applied as bioimaging materials.