Coherent spin dynamics of excitons in quantum wells is investigated th
eoretically. Resonant and nonresonant excitation conditions are consid
ered. The single-particle hole spin-flip mechanism within the exciton
is always the dominant cause for breaking the exchange coupling. The t
wo-dimensional confinement and low temperature are the most important
factors which stabilize the hole spin orientation within the exciton.
The experimental observations reported previously are interpreted.