Role of optical fiber drawing in radioluminescence hysteresis of Yb-Doped silica

Point defects in the host lattice of a scintillator material can trap carriers, slowing down their migration or even preventing their transfer to luminescent centers. Such competition scheme between defects and luminescent centers may explain also the hysteresis effect, which consists in a progressive enhancement of scintillation efficiency with accumulated dose. In this study we propose a comparison between the scintillation hysteresis effect of Yb-doped sol-gel silica glasses in form of bulk and fibers, and we correlate them with traps monitored by wavelength resolved thermally stimulated luminescence (WR-TSL) in both materials. The results demonstrate that the fiber drawing process is responsible for modifications of the defectiveness of the glass network, with a change of the local distribution of the traps surrounding the luminescent center. The consequence of such modifications is the removal, in the fiber samples, of the TSL peak ascribed to traps closer to Yb ions and unstable at room temperature. We highlight that suitable post-densification thermal treatments can really modify the concentration and spatial distribution of defects around a luminescent center and can therefore be used as a tool for the engineering of scintillating glasses.