  Popp and Yan [F. A. Popp, Y. Yan, Phys. Lett. A 293 (2002) 93] proposed a
model for delayed luminescence based on a single time-dependent coherent state.
We show that the general solution of their model corresponds to a luminescence
that is a linear function of time. Therefore, their model is not compatible
with any measured delayed luminescence. Moreover, the functions that they use
to describe the oscillatory behaviour of delayed luminescence are not solutions
of the coupling equations to be solved.
