Electron transfer between excited donor molecules followed by the back
reaction is treated theoretically for a solid solution at high excita
tion power. An expression for the average donor cation probability P+(
t) is derived. Calculations of the time dependence for P+(t) are prese
nted. The results indicate that the maximum value of P+(t) in the nonl
inear quenching process is less than the corresponding values of P+(t)
for the linear quenching at a low excitation power due to the depleti
on of the accepters with time t. The restriction of the reaction volum
e slows down the charge separation if the back charge transfer takes p
lace.