Room-Temperature Exciton Storage in Elongated Semiconductor Nanocrystals

The excited state of colloidal nanoheterostructures consisting of a spherical CdSe nanocrystal with an epitaxially attached CdS rod can be perturbed effectively by electric fields. Field-induced fluorescence quenching coincides with a conversion of the excited state species from the bright exciton to a metastable trapped state (dark exciton) characterized by a power-law luminescence decay. The conversion is reversible so that up to 10% of quenched excitons recombine radiatively post turn-off of a $1\mu \mathrm{s}$ field pulse, increasing the delayed luminescence by a factor of 80. Excitons can be stored for up to ${10}^5$ times the natural lifetime, opening up applications in optical memory elements.