Relaxation Dynamics of Excited States in Mn2+-Doped ZnCdS (Core)/ZnS (Shell) Quantum Dots Ions in Propylene Carbonate

It has been shown that luminescence in Mn@Zn0.49Cd0.51S/ZnS quantum dots (QDs) in propylene carbonate is due to a single Mn2+(4T1 → 6A1) band and has a quantum yield of ~24%. The Mn2+(4T1) level is excited through the light absorption in the exciton absorption bands of Zn0.49Cd0.51S/ZnS. The femtosecond dynamics of the difference spectra of Mn@Zn0.49Cd0.51S/ZnS QDs show fast relaxation of the exciton on the subpicosecond–picosecond timescale. At delay times in picosecond range, the band of stimulated luminescence has been detected in difference absorption spectra in the Mn2+(4T1 → 6A1) transition region. A qualitative hypothetical mechanism of nonradiative energy transfer from the exciton to Mn2+(4T1) involving the Auger transition in the trap states has been proposed. The assumption solves the problems of the energy excess of 0.98 eV in the energy transfer to the 3d5 level of Mn and of the conservation of the total spin of the system.