Figure 5: Multistate sensitization mechanism.
From: A graphene quantum dot photodynamic therapy agent with high singlet oxygen generation

(a) Schematic illustration of the 1O2 generation mechanisms by conventional PDT agents (left) and GQDs (right). (b) Fluorescence intensity of GQDs at 680 nm versus the O2 concentration in solution. (c) The dependence of the 1O2 quantum yield (QΔ) on the fluorescence intensity ratio at 680 nm (F/F0).