Luminescence Saturation
via Mn<sup>2+</sup>–Exciton
Cross Relaxation in Colloidal Doped Semiconductor Nanocrystals
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Abstract
Colloidal Mn<sup>2+</sup>-doped semiconductor nanocrystals
such
as Mn<sup>2+</sup>:ZnSe have attracted broad attention for potential
applications in phosphor and imaging technologies. Here, we report
saturation of the sensitized Mn<sup>2+</sup> 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<sup>2+</sup> ion and an exciton
within the same nanocrystal. A lower limit of <i>k</i> =
2 × 10<sup>10</sup> s<sup>–1</sup> is established for
the fundamental rate constant of the Mn<sup>2+</sup>(<sup>4</sup>T<sub>1</sub>)-exciton cross relaxation