Luminescence Saturation via Mn 2+ –Exciton Cross Relaxation in Colloidal Doped Semiconductor Nanocrystals

Colloidal Mn 2+ -doped semiconductor nanocrystals such as Mn 2+:ZnSe have attracted broad attention for potential applications in phosphor and imaging technologies. Here, we report saturation of the sensitized Mn 2+ photoluminescence intensity at very low continuous-wave (CW) and quasi-CW photoexcitation powers under conditions that are relevant to many of the proposed applications. Time-resolved photoluminescence measurements and kinetic modeling indicate that this saturation arises from an Auger-type nonradiative cross relaxation between an excited Mn 2+ ion and an exciton within the same nanocrystal. A lower limit of k = 2 × 10 10 s –1 is established for the fundamental rate constant of the Mn 2+ ( 4 T 1 )-exciton cross relaxation.