Thermoluminescence and optically stimulated luminescence of colemanite-rich borate mineral

We report structural, chemical composition, thermal decomposition and stimulated luminescence properties of a colemanite-rich borate (Ca2B6O11•5H2O) mineral collected from Kırka, Eskişehir region of Turkey. X-ray diffraction shows that the colemanite phase has a monoclinic crystal structure. Further, Raman spectroscopic analysis reveals that the sample contains 45.83% of B and 17.93% of CaO. Thermogravimetric analysis indicates that there is removal of hydroxyl groups followed by explosive release of water from the sample at temperature below 200 °C. The sample produces thermoluminescence (TL) and optically stimulated luminescence (OSL) following beta irradiation. A TL glow curve measured at 1 °C/s consists of five glow peaks at ∼145, 175, 215, 267 and 322 °C. The activation energy associated with the peaks are ∼0.73, 0.77, 0.83, 0.90 and 1.19 eV respectively and the frequency factors are ∼106 ‒ 108 s−1. The lifetimes of the traps at room temperature are estimated to be ∼1.42 days to 2.33 × 104 years. The peaks at ∼175, 215 and 267 °C show supralinear dose response between 32 and 16000 Gy whereas the ones at ∼145 and 322 °C show supralinearity between 32 and 2048 Gy. Analysis of the OSL decay curve shows that the decay curve has a ‘fast’-, ‘medium’- and a ‘slow’ component. The dose response of the fast component is found to be linear within 2–4096 Gy and that of the medium- and slow components are found to be superlinear between 2 Gy and 4096 Gy.