pH dependent stabilization of S2Q A (-) and S 2Q B (-) charge pairs studied by thermoluminescence.

The pH dependence of emission peak temperature and decay time of thermoluminescence arising from S2QB (-) and S2QA (-) recombinations demonstrates that a stabilization of S2QB (-) occurs at low pH whereas stabilization of S2QA (-) occurs at high pH. Based on comparative analysis of thermoluminescence parameters of the two types of recombination, we suggest that in the pH range between 5.3 and 7.5, Em(S2/S1) and Em(QA/QA (-)) are constant, but Em(QB/QB (-)) gradually increases with decreasing pH, while in the pH range between 7.5 and 8.5, an unusual change occurs on S2QA (-) charge pair, which is interpreted as either a decrease in Em(S2/S1) or an increase in Em(QA/QA (-)).