PL, TL and Persistent Luminescence Characterization of Undoped and Eu Doped Nanostructured Hydroxyapatite

Abstract

Hydroxyapatite (HAp, Ca10(PO4)6(OH)2) possesses the closest mineralized structure to natural bone tissue and has been widely using in as bone substitutes and for various biomedical applications. Undoped and doped with rare earth elements HAps are the basis of promising biomedical imaging, bone tissue engineering, gene and drug delivery applications. In the present work, we present the results of investigation of the photoluminescence (PL), thermoluminescence (TL) and persistent luminescence (PersL) of synthetic nanostructured HAp (n-HAp). Undoped and Eudoped (0.0, 0.1, 0.5, 1.0, 2.0 mol %) n-HAp powders were synthesized by solution-precipitation method and characterized by SEM-EDS, FTIR and Raman techniques. The 3D excitation-emission spectrum of undoped n-HAp exhibits a broad band with excitation/emission maximum at 376/454 nm, respectively. The maximum position slightly shifts to shorter excitation and emission wavelengths with increases of the Eu concentration that could be due to a possible overlapping between the Eu emission band and intrinsic emission of undoped n-HAp. It was found that (similarly to behavior of PL in Si nanocrystals, Xin et al., RSC Adv., 2019, 9, 8310) the emission peak is red-shifted as the excitation wavelength red-shifts. The typical Eu3+ emission bands were observed for high Eu doping concentrations. TL glow curves of n-HAp samples exposed to beta radiation from Sr-Y source display a broad TL peak with maxima in-between 145 and 165 oC depending on the Eu concentration. The highest TL intensity is observed for undoped n-HAp, showing quenching effect of Eu on TL emission. This TL quenching effect contrasted with the PersL decay emission measured immediately after irradiation exposure, which was highest for 0.1 mol % Eu. The intrinsic defects in n-HAp host is related to the PL, TL and PersL emissions; however, the nature of the radiative and non-radiative recombination mechanisms requires further investigation. The PL, TL and PersL of undoped HAp may have prospective application in the fields of radiation detection, ionizing radiation dosimetry and biomedical imaging. Keywords: Hydroxylapatite, thermoluminescence, persistent luminescence.