Enhanced OSL emission from $\alpha$-Al$_2$O$_3$ produced in the presence of halloysite nanocrystals

Abstract

This paper developed a seed-mediated synthesis of $\alpha$-Al$_2$O$_3$ by the combustion method using halloysite nanocrystals as seeds and analyzed the dosimetric characteristics of these samples, including radioluminescence (RL), thermoluminescence (TL), and optically stimulated luminescence (OSL). Both SEM images and XRD pointed to the halloysite nanotubes acting as heterogeneous nucleation seeds. RL spectra indicate the presence of Cr$^{3+}$ ions due to impurities from the precursors. However, besides acting as nucleation seeds, the halloysite nanotubes were still able to adsorb the Cr$^{3+}$ ions, as evidenced by the decreased RL emission attributed to the Cr$^{3+}$ luminescent centers. Decreased TL intensity upon increasing HNT content together with the RL data suggested that the Cr$^{3+}$ ions have strong participation in the TL emission process as a luminescent center. Surprisingly, the samples with HNT showed up to 6-fold enhanced OSL area intensity and 69-fold OSL initial intensity enhancement, revealing that, by scavenging Cr$^{3+}$, the HNT eliminated a luminescent center that competes with the OSL emission. Therefore, HNTs are promising nanomaterial to enhance the sensitivity of $\alpha$-Al$_2$O$_3$ dosimeters with potential application in medical physics, revealing that the presence of HNT in Al$_2$O$_3$ decreased the density of competing for luminescent centers and increased OSL intensity.