Multiexcitons in colloidal semiconductor nanocrystals

The study of multiexcitons in colloidal quantum dots (CQDs) is a timely topic, as these multiexcitons have practical applications in gain devices, photovoltaic cells and as single photon light sources. However, these excitons decay primarily via nonradiative Auger relaxation at a time scale of 10-100 ps, due to the enhancement of many-body interactions inside dots with a typical diameter of 3-4 nm surrounded by low dielectric medium. Despite the predicted limitations, the present study unambiguously showed an emission of neutral biexciton (BX), triexciton (TX) and quandraexciton (QX) in a time-integrated micro-photoluminescence (mu-PL) spectrum of quasi-type II CdTe/CdSe CQDs. These CQDs offer the option of Auger relaxation suppression and an extension of multiexcitons´ lifetime. This upturn should permit charge extraction in photovoltaic cells and inversion of population in a gain device.