Near-Unity Biexciton Quantum Yields in Individual Giant Nanocrystal Quantum Dots

We report quantitative studies of photoluminescence (PL) quantum yields of biexcitons ($Q_{BX})$ in individual CdSe/CdS core/shell nanocrystal quantum dots (NQDs) as a function of shell thickness. $Q_{BX}$s measured by two independent techniques show a gradual increase with increasing shell thickness, reaching a near-unity value of $\sim $0.9 for the NQDs with a 19 monolayer-thick shell. These results imply a strong suppression of Auger decay.~ However, $Q_{BX}$s show a wide variation among nominally identical NQDs implying a strong dependence of $Q_{BX}$ on subtle structural differences of the core/shell interfaces. Surprisingly, despite a wide variation in $Q_{BX}$, all thick-shell NQDs exhibit a complete suppression of PL blinking, implying that this non-blinking behavior does not result from the suppression of Auger decay and instead may simply arise from a reduced likelihood of photocharging.