Multiexponential dynamics of Mn2+(3d5) excitation in manganese doped ZnCdS quantum dots: Stimulated emission band in femtosecond transient spectra reveals ultrafast nonradiative energy transfer to Mn2+(3d5)

Abstract

Stimulated emission (SE) 4T1 → 6A1 bands of Mn2+(3d5) in ZnxCd1−xS or ZnxCd1−xS/ZnS quantum dots were detected in the femtosecond transient absorption spectra at a time delay of 120 fs. Multiexponential rise of SE(Mn2+) amplitude due to nonradiative energy transfer to Mn2+(3d5) occurs both in the femtosecond and picosecond time domain. Transient kinetics of SE(Mn2+) band reveals the dynamics of energy transfer to Mn2+(3d5) with time constants τ1 ~ 400–600 fs, τ2 ~ 4–6 ps and τ3 ~ 87–112 ps. A possible mechanism of ultrafast energy transfer to the Mn2+(3d5) center accompanied by spin-flip is discussed.