Local Structure and Photoluminescence Decay Dynamics in Undoped and Mn$^{2+}$ Doped ZnSe Nanoparticles

Undoped and Mn$^{2+}$-doped ZnSe nanoparticles were synthesized from molecular cluster precursors. The nanoparticles were characterized using UV-VIS, PL, ESR, and XAFS. These studies confirmed the presence if Mn$^{2+}$ dopant in the host ZnSe lattice, and suggested the existence of two distinct Mn$^{2+}$ sites in the ZnSe lattice. Energy transfer dynamics in Mn$^{2+}$-doped ZnSe nanoparticles were also studied using time-integrated and time-resolved spectroscopic techniques. Time-resolved picosecond PL and femtosecond transient absorption studies show that the Mn$^{2+}$ doping substantially shortens the lifetimes of both the bandedge excitonic states and the shallow trap states. Energy transfer from ZnSe to Mn$^{2+}$ likely follows two mechanisms: one that involves mediation through trap states and another without.