Thermoluminescence and anomalous heating-rate behavior in SmBa3B9O18: Evidence for hierarchical trap distribution and strong retrapping dynamics

Abstract

SmBa3B9O18 nanostructures were synthesized by a sol-gel assisted microwave combustion route and subsequently calcined at 800 degrees 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 degrees C for 8 s effectively removes shallow traps and stabilizes the dosimetric signal, yielding dominant glow peaks at similar to 220 degrees C and similar to 290 degrees C associated with thermally stable trapping centers. The material shows a nearly linear dose response up to similar to 60 Gy, followed by controlled supralinearity up to 500 Gy, together with a low minimum detectable dose (similar to 0.13 Gy) and excellent reusability, with cycle-to-cycle deviations within +/- 5%. Variable heating-rate experiments (0.2-4 degrees 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 similar to 1.6-1.7 eV and similar to 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 similar 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.