Thermoluminescence and anomalous heating-rate behavior in SmBa₃B₉O₁₈: Evidence for hierarchical trap distribution and...

SmBa₃B₉O₁₈ nanostructures were synthesized by a sol-gel assisted microwave combustion route and subsequently calcined at 800 °C, yielding a crystalline rare-earth-based borate host lattice for detailed thermoluminescence (TL) characterization. X-ray diffraction and Rietveld refinement confirm the formation of a single-phase structure with high crystallinity and well-defined lattice parameters. TL measurements recorded in a 565 nm band-pass detection window reveal well-resolved multi-peak glow curves suitable for detailed kinetic analysis. Preheating at 150 °C for 8 s effectively removes shallow traps and stabilizes the dosimetric signal, yielding dominant glow peaks at ∼220 °C and ∼290 °C associated with thermally stable trapping centers. The material shows a nearly linear dose response up to ∼60 Gy, followed by controlled supralinearity up to 500 Gy, together with a low minimum detectable dose (∼0.13 Gy) and excellent reusability, with cycle-to-cycle deviations within ±5%. Variable heating-rate experiments (0.2-4 °C s^-1) reveal pronounced anomalous heating-rate behavior, where both peak intensity and integrated TL signal increase with heating rate, deviating from conventional kinetic models. Combined various-heating-rate, T_m-T_stop and initial-rise analyses (with thermal-lag correction) yield activation energies of ∼1.6-1.7 eV and ∼1.9-2.0 eV for the main peaks and reveal characteristic plateau-shift behavior consistent with a hierarchical trap system comprising multiple overlapping and partially distributed trapping levels. Fading analysis shows non-monotonic behavior, with an initial TL increase of up to ∼20% around 12 h followed by gradual decay, attributed to post-irradiation charge redistribution and thermally assisted retrapping within a coupled trap system. These results demonstrate that SmBa₃B₉O₁₈ is a promising TL dosimetric material, combining high structural stability, sensitive and reusable response, and complex non-classical luminescence kinetics governed by coupled trap-recombination dynamics.