Photoluminescence of thermoluminescent dosimetric materials on the basis of aluminium and silicon oxides

Full text: Presently, the materials on the basis of α-Al2O3 with anion defect and amorphous SiO2 are quite commonly used in dosimetric practice. One of the important characteristics of α-Al2O3 in terms of ionizing radiation dosimetry is its high sensitivity to ultraviolet light (UV). Due to its high light sensitivity, the material can potentially be used as UV radiation detector. SiO2 is almost completely light-insensitive. The reason of so strong distinction in similar materials should find an explanation. This study attempts to explain the above-discussed phenomenon through a detailed investigation of photoluminescence. When TLD-KM (on the basis of SiO2) and TLD-500 (on the basis of α-Al2O3) are irradiated with typical individual dosimetry doses, a single primary thermoluminescence peak is observed at 455 K and 435 K respectively. At higher irradiation doses (>1 Gy), both systems exhibit higher temperature peaks at approximately 570 - 590 K. In the thermoluminescence spectrum of the primary dosimetric peak of TLD-LM (SiO2), luminescence is observed at approximately 300-400 nm and 600-700 nm. In thermoluminescence spectra of dosimetric α-Al2O3 with anion defect luminescence is observed at about 330 nm (F+-centers), 410-420 nm (F - centers), and 690 nm luminescence due to Cr3+ impurity). Absorption spectra of the realistic detectors do not exhibit a clearly defined structure. A fundamental absorption edge is observed at about 100 nm in the absorption spectrum of TLD-KM detector; TLD-500 is relatively transparent all the way to 210 nm. Absorption bands F and F+ (203,230, and 255 nm) are not clearly visible for the realistic detector. As TLD-500 (α-Al2O3 with anion defect) is exited to the absorption region (210, 230, and 260 nm), luminescence due to F+ - center irradiation is observed at 330 nm in the luminescence spectrum [1]. In the excitation spectrum of F+ - center luminescence, well-defined bands occur at 230, 250, and 260 nm, with the maximum at 260 nm. At 210 nm excitation of the 330 nm band is weak. A close investigation of the kinetics of the 330 nm luminescence in the microsecond range allows to draw a conclusion that τ≤1 μs. We did not register any F-center luminescence in the microsecond time-range following photoexcitation of TLD-500. Therefore, high light sensitivity of TLD-500 is most likely determined by a highly efficient mechanism of F+ - center excitation by short wave UV. In the luminescence spectrum of TLD-KM dosimeters, overlapping bands at 360 nm (F-centers) and 400 nm (Al) are observed, with the maximum excitation of 330 nm. There is no TLD-KM luminescence excitation in the short wave UV region. Therefore, light sensitivity of TLD-500 is most likely related to the existence of an efficient channel of F+ excitation in the UV region of the spectrum