Hydroxyapatite Nano- and Microcrystals with Multiform Morphologies: Controllable Synthesis and Luminescence Properties

Hydroxyapatite (Ca 5 (PO 4 ) 3 OH) nano- and microcrystals with multiform morphologies (separated nanowires, nanorods, microspheres, microflowers, and microsheets) have been successfully synthesized by a facile hydrothermal process. X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), photoluminescence (PL) spectra, kinetic decay, and electron paramagnetic resonance (EPR) were used to characterize the samples. The experimental results indicate that the obtained Ca 5 (PO 4 ) 3 OH samples show an intense and bright blue emission under long-wavelength UV light excitation. This blue emission might result from the CO 2 •− radical impurities in the crystal lattice. Furthermore, the organic additive (trisodium citrate) and pH values have an obvious impact on the morphologies and luminescence properties of the products to some degree. The possible formation and luminescent mechanisms for Ca 5 (PO 4 ) 3 OH nano- and microcrystals are presented in detail.