Abstract <p>A detailed theoretical analysis of the three-level Jablonski diagram describing the processes of fluorescence, phosphorescence, and delayed fluorescence is presented. The excitation behavior is quantitatively described, and the formulas for calculating the quantum yield of delayed fluorescence and phosphorescence have been refined. Based on the derived equations, the dependence of luminescence quantum yields and lifetimes on the singlet–triplet energy gap and the intersystem crossing rate constant has been calculated using InP colloidal quantum dots doped with Mn²⁺ ions as a model system.</p>