Excitation Source for visible emitting Quantum dots

I read that the best excitation source for visible emitting quantum dots is UV light of wavelength $\mathrm{360~nm}$ to $\mathrm{380~nm}$. But why should the excitation source have lower frequency than the desired emission maximum?


If the excitation source have lower frequency, the energy of photons in the source will be lower. If that is the case wouldn't it have insufficient energy to excite the electrons from valence to conduction band?


