Preliminary study of the thermally stimulated blue luminescence of ulexite

Thermoluminescence sensitivity of ulexite after UV irradiation

“…In addition, a third maximum is observed at (ii) 240°C (associated with the Na coordination chain dehydroxylation and the starting point of the alkali self-diffusion through the lattice). A weaker maximum can also be observed (at 340°C) and is most likely due to the amorphization of the lattice [27]. All such components are sensitive to UV exposure, thereby producing an increase in the TL intensity with increasing irradiation duration.…”

“…As shown in Fig. 2a, the TL glow curve at RT consists of three groups of components, where two intense maxima occur at (i) 130-140°C, which can be linked to dehydration and creation-annihilation of the triple-hydrated phases of the neo-formed crystallographic structure [27]. The microstructure of this mineral exhibits a very complex texture and consists of fibrous aggregates, elongated crystals running in parallel along the c-axis [0 0 1].…”

“…The microstructure of this mineral exhibits a very complex texture and consists of fibrous aggregates, elongated crystals running in parallel along the c-axis [0 0 1]. According to Correcher et al, [27] the fiber-axis optical direction Ca-polyhedral and Na-octahedral chains dominate the structure and are responsible for the fibrous nature of ulexite at RT. The increase in temperature from RT up to 131°C induces changes in the structure of this material that can be associated with the phase transition between the pentahydrated and a triple-hydrated phase due to the formation-annihilation of this triple-hydrated phase.…”

“…2b). Soft thermal treatment (up to 50°C) produces negligible changes in the ulexite structure [27]; however, the UV exposure at 50°C induces significant changes in the TL intensity. The exposure produces an increase in the glow emission, which affects, in a different manner, each group of components when compared to the RT measurements.…”

“…2d, the TL intensity of the remaining components (peaks 1 and 2) increases linearly with increasing UV exposure. The increase in temperature (up to 100°C) induces dehydration that is detected not only on the ulexite surface [27] but also in the TL response. This thermal effect leads to the TL signal showing that (i) the ratio between the first and second peak is close to 1:5 for 10 min of illumination.…”