Paper MI-ThM8
Size-Dependent Excited State Dynamics in Mn²⁺-Doped CdSe Quantum Dots

Thursday, October 18, 2007, 10:20 am, Room 619

Colloidal Mn²⁺-doped II-VI quantum dots are interesting materials for the study of magnetic and luminescent phenomena in quantum confined semiconductor nanostructures. In recent years, several reports have described luminescence, absorption and magnetism of Mn²⁺-doped ZnS, CdS and ZnSe quantum dots. In general, the emission properties of these nano-scale materials behave much like their bulk counterparts, showing a size insensitive Mn²⁺ ligand-field emission with a long lifetime. In contrast, Mn²⁺-doped CdSe nanoparticles are expected to behave differently from bulk because of the possibility of size-tuning the band-gap energy from below to above the Mn²⁺ emitting level. For this reason, Mn²⁺-doped CdSe offers an interesting opportunity for fundamental studies of quantum confinement effects in doped semiconductors. Curiously, although photoluminescence spectra of self-assembled Mn²⁺ quantum dots prepared by vacuum deposition have been reported, the Mn²⁺ is either absent of only tentatively reported, even for high Mn²⁺ concentrations. Moreover, CdSe excitonic emission is observed despite the fact that the energy gap is greater than the Mn²⁺ excitation energy. We recently presented a new method for preparing colloidal doped CdSe quantum dots.¹ Importantly, these particules show a giant Zeeman splitting of their excitonic transitions, as is expected for diluted magnetic semiconductors. Here we will describe the temperature-dependent photoluminescence of these particles, which gives insight into the energy transfer dynamics in Mn²⁺-CdSe quantum dots. A kinetic model will be described that explains the paradoxical absence of Mn²⁺ emission in Mn²⁺-doped CdSe quantum dots reported previously.

¹ Archer, P. I.; Santangelo, S. A.; Gamelin, D. R., Nano. Lett., 7, 1037-1043 (2007).