Intraband relaxation in CdSe quantum dots

The relaxation of the 1P to 1S electronic states of CdSe semiconductor nano crystals is followed by infrared pump-probe spectroscopy. Fast (1 ps) and s low (>200 ps) components are-observed. Using different capping molecules to control the hole states, we show how the intraband relaxation slows down a s the hole is in a shallow trap, a deep trap, or a charge-separated complex , providing strong support for an electron-hole Auger coupling. The slow co mponent corresponds to an energy relaxation rate orders of magnitude slower than in bulk systems. It may be the first indication of the phonon bottlen eck effect long expected in strongly confined quantum dots. [S0163-1829(99) 51128-4].