Abstract
Fully inorganic lead halide perovskite nanocrystals (NCs) are of interest for optoelectronic and light-emitting devices because of their photoluminescence (PL) emission properties, which can be tuned/optimized by (I) surface passivation and (II) doping. (I) Surface passivation of the NC affects PL capabilities, as an underpassivated surface can introduce trap states, which reduces PL quantum yields. (II) Doping NCs and quantum dots with transition-metal ions provides stable optical transitions. Doping perovskite NCs with Mn 2+ ions provides high-intensity 4 T 1 → 6 A 1 optical transitions in addition to the bright intrinsic NC emission. Here, we use noncollinear density functional theory (DFT) to investigate the roles of surface passivation and doping on the PL emission stability of perovskite NCs. Two models are investigated: (i) a pristine NC and (ii) a NC doped with the Mn 2+ ion. The noncollinear DFT includes spin–orbit coupling (SOC) between different spin states and produces spin adiabatic molecular orbitals. These orbitals are used to calculate the transition dipoles between electronic states, oscillator strengths, radiative transition rates, and emission spectra. It was found that the noncollinear spin basis with SOC slows down hole relaxation in the doped NC by 2 orders of magnitude compared to spin-polarized basis. This is attributed to “spin-flip” transition from the perovskite NC to the Mn 2+ dopant and low-probability nonradiative d - d transition.