In-Vacuo thermal processing of α-Al2O3 single crystals in boron ambience and its implication on TL & OSL response

Single crystals of α-Al2O3 (10×10 mm2, 0.4 mm thick) were annealed in vacuum at about 1500 °C in the ambience of boron. The OA studies on these samples showed bands at 203, 232 and 258 nm signifying that such a treatment leads to the formation of F and F+ centers in significant concentrations, these bands, however, were not found in the Al2O3 crystals processed in the similar manner in the absence of boron. The Al2O3:B samples were irradiated to different absorbed doses of 90Sr/90Y β-source and the continuous wave OSL (CW-OSL) was recorded on the samples using 470 nm blue light stimulation. These samples have shown a linear TL and CW-OSL response in the dose range of 20 mGy to 15 Gy. The minimum detectable dose, corresponding to 3σ limit of the variation of the output of the unirradiated dosimeters, was found to be 100 μGy. Irradiated samples stored in dark at room temperature for a period of two months show negligible fading. The TL and OSL sensitivities of the samples were found to be strongly dependent on process temperature and time. The TL response is marked by the absence of low temperature peak (<100 °C), unlike the case of α-Al2O3:C, implying that the boron doping does not lead to formation of shallow traps. The Al2O3:B samples show faster photoionisation cross-section as compared to α-Al2O3:C. This approach of processing of single crystal Al2O3 in the boron ambience thus represents a potential way of introducing dosimetrically pertinent defects in Al2O3 single crystals.