Electron-hole overlap dictates the hole spin relaxation rate in nanocrystal heterostructures.

Hole spin relaxation dynamics in CdTe/CdSe core-shell nanocrystals are measured by an ultrafast polarization transient grating technique. Photoexcited charge separation in type II structures suppresses the electron-hole exchange interaction and the hole spin relaxation time constant is found to increase from ∼0.3  ps to ∼10  ps at 293 K as the CdSe shell thickness increases from ∼0.2  nm to ∼2.4  nm. Analysis of these data suggests that spin relaxation in semiconductor nanostructures is tunable between type I and type II localization according to an electron-hole overlap function.