Anomalous regeneration of OSL in sodium chloride – Experiment and modeling

• Optically stimulated luminescence (OSL) of sodium chloride (NaCl) was studied.
• The measurements were performed using the variable delay OSL method (VD-OSL).
• It was found that the increase of OSL intensity in NaCl could be as high as 190%.
• A simple phenomenological model for regeneration and fading is proposed.
• The model predicts peak shaped character of OSL traps population.

Recently, a new optical phenomenon was observed in sodium chloride (NaCl). Performing series of optically stimulated luminescence (OSL) readouts it was found that subsequent OSL decay, after some delay, starts from significantly higher intensity level than the final intensity of the previous readout. This unusual behavior was called the ‘regeneration effect’ (Biernacka and Mandowski, 2013). Regeneration occurs in spite of the significant fading of OSL – well known in this material. Nevertheless, these two contradictory processes take place in two different time scales. Previously, it was proved also, that the regeneration phenomenon cannot be explained on the basis of the classical simple trap model (STM). This paper analyses optimal measurement conditions leading to the highest regeneration effect. It was found that the increase of OSL intensity could be as high as 190%. A simple phenomenological model explaining the mechanism of regeneration is proposed. The model involves simultaneous localized and delocalized (i.e. band-like) transitions. Characteristic lifetimes of regeneration and fading processes are of the order of 560 s and 22000 s, respectively.