Synthesis and optimization of Nd3+doped hydroxyapatite as NIR-to-NIR nanothermometers

Abstract

Neodymium (Nd)-doped nanomaterials show excellent biothermal sensing (TS) properties due to the thermally coupled near-infrared (NIR) emission. However, Nd-doping in biomaterials like hydroxyapatite (HA) may offer added biocompatibility, a major concern for TS materials. Here we report the optimisation of Nd-doped hydroxyapatite (HAP) nanophosphors as potential nanothermometers operating within the biological windows. Different doping concentrations were analysed where 5% Nd3+ doped HAP (HAP:5%Nd) showed the highest luminescence output, which improved 4-fold after the annealing. Thus, the effect of annealing was also analyzed on optical properties and thermal sensing. The ratiometric luminescence thermal sensing of HAP:5%Nd revealed the linear behaviour in the temperature range of 25– 60 °C with a high relative thermal sensitivity value of 0.37% K−1 at 298 K. Furthermore, the synthesized nanocrystals showed excellent biocompatibility in vitro. Overall, HAP:5%Nd showed properties for implementation in biomedical applications.