Non-classical thermoluminescence kinetics and inverse fading behavior in K7CaGd2(B5O10)3 phosphor

Abstract

The thermoluminescence (TL) properties of the newly synthesized K7CaGd2(B5O10)3 phosphor were systematically investigated to assess its potential for dosimetric applications. A prominent TL peak near 220 ◦C was observed, accompanied by additional features indicating a complex trap structure. Activation energies were calculated using variable heating rate (VHR) methods, including refined Hoogenstraaten and Booth–Bohun–Parfianovitch approaches, with corrections applied for thermal lag to improve accuracy. VHR analysis of the dominant dosimetric peak yielded activation energies consistent with an apparent first-order approximation, as evidenced by the linearity of the corrected kinetic plots. Tm–Tstop and initial rise (IR) methods revealed thirteen discrete trap levels with activation energies ranging from 1.17 to 2.09 eV. Complementary computerized glow curve deconvolution (CGCD) analysis provided a fitting-based decomposition consistent with this rich trap distribution: thirteen overlapping TL peaks were resolved before preheating, with frequency factors up to ~1017 s 1, which may be consistent with the presence of spatially correlated trapping and recombination centers. Following preheating, thermally unstable shallow traps were removed, isolating eight stable peaks (Ea = 1.21–2.09 eV), and demonstrating the effectiveness of thermal treatment in enhancing signal stability. The phosphor showed a linear dose–response over the range of 1.4–30.1 Gy, indicating stable behaviour within the investigated mid-dose region. A reproducible increase of approximately a 20-fold enhancement in TL signal was observed within 12 h of storage under controlled laboratory conditions, deviating from classical fading behaviour. This trend may represent an inverse fading–like response, potentially driven by delayed recombination, quantum mechanical tunnelling, or charge redistribution among metastable trap configurations. Despite the near-first-order behaviour of the main dosimetric peak, the overall TL response exhibited non-classical characteristics, including heating-rate-dependent intensity enhancement (0.1–10 ◦C/s) and time-dependent signal amplification. These observations suggest that, while the dominant trap behaves quasi-independently under standard kinetic evaluation, the broader trapping–recombination system likely involves semi-localized or dynamically evolving recombination processes. Overall, these findings demonstrate that K7CaGd2(B5O10)3 exhibits structurally rich and thermally stable trapping characteristics within the investigated β-dose regime. However, further studies addressing low-dose response, photon-energy dependence, and comparison with established dosimetric standards are required before broader practical applications can be considered.