Effect of Manganese Doping on Optical Properties of HgSe Quantum Dots.

We consider stoichiometric and non-stoichiometric HgSe QDs ranging from 1 to 2 nm in size, with Wurtzite (WZ) and Zinc Blende (ZB) crystal lattice symmetry incorporating an ion of Mn(II) as a doping at various positions at the crystal lattice. For the non-stoichiometric case, we have modeled a “core” doping located at roughly the center of the QD, and a “shell” doping located at an un-passivated edge of the surface. The stoichiometric wurtzite and Zinc Blende cases were modeled with placing doping on each surface of the QD with distinct crystal symmetry. Halogen atoms (F, Cl, Br) passivate under-coordinated surface mercury atoms. Using Density Functional Theory (DFT) and Time Dependent DFT (TDDFT), we have found that halogen ligands notably increase intensities of the lower-energy transitions at around 500 nm for all systems. Additionally, “shell” doped systems show greater oscillator strength at lower energies compared to the “core” doped systems. Visualization of the natural transition orbitals (NTOs) contributing to these transitions explain these high oscillator strengths by delocalization of the electron density from Mn atom to the rest of the QD.