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The optical properties of hybrid molecules composed of semiconductor and metal nanoparticles with a weak probe in a strong pump field are investigated theoretically. Excitons in such a hybrid molecule demonstrate novel optical properties due to the coupling between exciton and plasmon. It is shown that a non-absorption hole induced by coherent population oscillation appears at the absorption spectrum of the probe field and there exists slow light effect resulting in the great change of the refractive index. The numerical results indicate that with the different center-to-center distance between the two nanopaticles the slow light effects are greatly modified in terms of exciton-plasmon couplings.
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