Temperature- and Mn Concentration-Dependent Emission Properties of Mn-Doped ZnSe Nanocrystals.

Mn-doped ZnSe nanocrystals (Mn:ZnSe d-dots) with high optical quality-high dopant emission quantum yield with monoexponential dopant-emission decay dynamics-enable systematic and quantitative studies of temperature- and Mn concentration-dependent optical properties of the dopant emission, especially its relationship with magnetic coupling. While temperature-dependent steady-state and transient dopant emission of d-dots with dilute Mn concentrations originated from isolated Mn ions, and can be quantitatively treated as a result of exciton-phonon coupling of isolated paramagnetic emission centers. Dopant emission of d-dots with high Mn concentrations (up to 50% of Zn ions being replaced by Mn ions in the core nanocrystals) are found solely related to magnetically coupled Mn emission. Magnetic coupling effects on steady-state dopant emission of d-dots with high Mn concentrations are much stronger than those observed for doped bulk semiconductors, which is found to follow a strong and universe shell-thickness dependence for the epitaxial ZnSe and/or ZnS shells of the d-dots. By exciting the magnetically coupled Mn ions directly, dopant-emission of d-dots with high Mn concentrations exhibit monoexponential decay dynamics. In addition to this emission channel, a minor channel with slightly longer decay lifetime appears when the host nanocrystals with high Mn concentrations are excited, which is barely visible at room temperature and increases its fraction by decreasing temperature.