We have investigated the temperature dependence of an energy transfer (ET) between CdSe/ZnS quantum dots (QDs) measuring photoluminescence dynamics in a bilayer structure consisting of differently sized QDs. In the bilayer structure, an effective direct ET from donor QDs to acceptor QDs is realized. The temperature dependence of the observed ET rate can be classified into two categories. Under the condition that the thermal energy $\left(k_{B}T\right)$ is comparable to the splitting energy between the bright- and dark-exciton states and above, the observed ET rate is dominated by the thermal population behavior of the bright-exciton state: the ET rate increases with an increase in temperature. On the other hand, in the lower temperature region, the observed ET rate is almost constant, which may be due to a breakdown of the thermal equilibrium between the lower-lying dark-exciton state and the bright-exciton state.

• Received 15 March 2009

DOI:https://doi.org/10.1103/PhysRevB.80.045322