Is the Lack of Orange Emission Infallible Proof of Unsuccessful Doping of Mn in Quantum Dots?

Abstract

Manganese (Mn) is one of the most studied transition metal dopants to alter the optical properties of host semiconductor nanocrystals (NCs). In most cases, the doped NCs are characterized by an invariant broad photoluminescence (PL) spectrum at 2.12 eV. The nature of this emission, although thought to be atomic-like, has revealed several dependencies on the host NCs in recent literature that facilitates the energy/charge transfer to a spin and orbital forbidden channel. In this work, we study this transfer as a function of the host band gap and spin–orbit coupling. We demonstrate that while the energy/charge transfer is facilitated by the energy difference between the band gap and Mn excitation energy, the high spin–orbit coupling allows transfer and back transfer of energy/charge, thus giving rise to a tunable higher energy transition even in successful doping of Mn. We use low-temperature PL and gated PL to demonstrate this phenomenon.