Alloyed core/doped shell MnxZn1−xSe/ZnSe:Mn2+ nanocrystals: steady-state and time-resolved spectroscopy

Steady state and time-resolved optical properties of alloyed core/doped shell MnxZn1−xSe/ZnSe:Mn2+ nanocrystals with x between 0.2 and 1 were studied. The emission from Mn2+ ions at ~580 nm is predominant for higher MnSe mole fractions in the core (higher x). At lower fractions, the ZnSe excitonic emission is also present while the Mn2+ emission shifts to ~560 nm. The ratio of photoluminescence intensity of these emission bands depends on the composition of the alloyed core. The excited state lifetime of Mn2+ ions is also strongly dependent on the core composition, ranging from 300 μs for small MnSe mole fractions down to 65 μs for x=1. This is attributed to the long-range strain caused by a lattice mismatch of more than 4% at the core/shell interface. For x≤0.6, an additional lifetime, depending on the presence of an extra electron within the nanocrystals, was measured in the hundreds of nanoseconds range. A 4-level dynamic model is proposed to explain this observation.