“…The radiation trapping effect, which is also known as reabsorption effect, is illustrated in Figure 4 In the absence of strong lifetime quenching effect, as in the case of KRE(WO4)2:Yb 3+ [83], a higher concentration of active ions in the material increases the occurrence of the reabsorption process and leads to the observation of longer measured lifetimes [92]. Contrarily, with the presence of strong quenching, the lifetime initially increases with the increasing active ions concentration, after which it sharply decreases with the further increase of active ion concentration [27,83] [126]. This approach requires extensive sample preparation which is destructive in nature.…”