Luminescence Saturation via Mn2+-Exciton Cross Relaxation in Colloidal Doped Semiconductor Nanocrystals

Colloidal Mn2+-doped semiconductor nanocrystals such as Mn2+:ZnSe have attracted broad attention for potential applications in phosphor and imaging technologies. Here, we report saturation of the sensitized Mn2+ 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 Mn2+ ion and an exciton within the same nanocrystal. A lower limit of k = 2 x 10(10) s(-1) is established for the fundamental rate constant of the Mn2+(T-4(1))-exciton cross relaxation.