Influence of single and co-doped lanthanides on the thermoluminescence response of hydroxyapatite prepared by the hydrothermal method.

In this study, nanostructured hydroxyapatite (HAp) doped with lanthanide elements (Ce, Dy, Gd, and La at various concentrations of 1, 2, and 5 mol%) was synthesized by a hydrothermal method to evaluate its potential for high-dose radiation dosimetry. X-ray diffraction (XRD) analysis confirmed the formation of a pure hydroxyapatite phase in all samples with no detectable secondary phases, indicating successful dopant incorporation. Thermoluminescence (TL) measurements were performed after 60 Co gamma irradiation over a wide dose range of 20-3,000 Gy. The results showed that TL sensitivity is strongly dependent on dopant type and concentration; notably, 1 and 2 mol% Ce and Dy exhibited the highest sensitivities, while 5 mol% samples showed concentration quenching. The glow curves revealed prominent peaks, indicating good thermal stability and suitability for dosimetric applications. Kinetic parameters including activation energy (E) and frequency factor(s) were determined using Chen's peak-shape method, showing that Ce1, Ce2, and Gd5 samples follow first-order kinetics, which is favourable for dosimetric applications, as the glow peak maximum temperature ([Formula: see text]) remains independent of the absorbed dose. The TL behaviour of co-doped systems (Ce2Dy2, Ce2La2, La2Dy2, and Ce2Gd5) was also investigated. While co-doping altered the glow-peak structure and dosimetric properties, it generally exhibited an intermediate dosimetric performance between the corresponding single-doped constituents rather than a distinct synergistic enhancement. The co-doped compositions maintained higher TL sensitivity than the heavily quenched 5 mol% single-doped counterparts, though remaining below the optimum sensitivity achieved by 1-2 mol% single-doped samples. In addition, reproducibility tests over five irradiation-readout cycles showed acceptable stability, with relative standard deviations ranging from 3.6% for Gd2 to 13.2% for Ce2. Fading measurements also confirmed good signal retention, with the best co-doped sample retaining 86.5% of its TL response after 30 days. Overall, the high sensitivity, broad linear dose-response behaviour, with some compositions remaining linear up to 3,000 Gy, acceptable reproducibility, and favourable fading behaviour make Ce- and Gd-doped HAp promising candidates for environmental and industrial radiation dosimetry, while further low-dose investigations are required to assess their suitability for medical dosimetry.