Spinor Dynamics in Pristine and Mn²⁺-Doped CsPbBr₃ NC: Role of Spin–Orbit Coupling in Ground- and Excited-State Dynamics

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 highintensity 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.

Universal Size-Dependent Stokes Shifts in Lead Halide Perovskite Nanocrystals

“…Ground-state, electronic structure calculations implement noncollinear density functional theory (DFT) with spin–orbit coupling (SOC) included to generate spinor Kohn–Sham orbitals (SKSOs), . Inclusion of SOC corrections within SKSO calculations is critical for obtaining correct orbital symmetries and conduction band g SKSO s due to the large angular momentum of Pb 6p states. − Associated g SKSO s are computed using where ε i SKSO is the computed band energy and the Fermi level is defined as . Details of the atomistic model construction and electronic structure calculations can be found in the Supporting Information.…”

Concurrent Energy- and Electron-Transfer Dynamics in Photoexcited Mn-Doped CsPbBr3 Perovskite Nanoplatelet Architecture

“…6,7 The dopant Mn 2+ ions effectively replace some of the Pb 2+ ions in the octahedral environment to form the Mn 2+doped perovskites. 8 The impurity doping effectively modifies the inherent optical, magnetic, and electronic properties of the host nanocystals (NCs) and considerably alters the conventional carrier relaxation pathways by providing additional probable charge/energy-transfer routes in the doped NCs. 9−11 The most significant outcome of Mn 2+ doping is that a new state is introduced ( 4 T 1 _6 A 1 ) in the host NCs, which is mainly due to the Mn d−d transitions.…”

“…Plentiful research efforts have focused upon doping an all-inorganic perovskite crystal lattice, including Cu 2+ , Ni 2+ , Cd 2+ , Bi 3+ , and Mn 2+ to further improvise the efficiency and stability of the energy-harvesting devices. − Among them, the synthetic strategy employing Mn 2+ doping of the all-inorganic perovskites has so far displayed the most fascinating properties compared to those exhibited upon doping by the other dopants. , The dopant Mn 2+ ions effectively replace some of the Pb 2+ ions in the octahedral environment to form the Mn 2+ -doped perovskites . The impurity doping effectively modifies the inherent optical, magnetic, and electronic properties of the host nanocystals (NCs) and considerably alters the conventional carrier relaxation pathways by providing additional probable charge/energy-transfer routes in the doped NCs. − The most significant outcome of Mn 2+ doping is that a new state is introduced ( 4 T 1 _6 A 1 ) in the host NCs, which is mainly due to the Mn d–d transitions.…”

Brightly Luminescent CsPbBr3 Nanocrystals through Ultracentrifugation

“…Despite these rather complex surface chemistries and the associated challenges related to colloidal and material stability, the photophysics and photochemistry of LHP nanocrystals (NCs) are quite promising, with bright photoluminescence (PL), fast PL lifetimes, and narrow PL line widths combined with broad color tunability through precise control of the chemical composition . They exhibit numerous interesting photophysical effects that are distinct from analogous semiconductor NC systems, including a defect tolerant electronic structure , in part due to large spin–orbit coupling, , bright triplet excitons, deliquescent salt treatment as a way to achieve near-unity PL quantum yield (QY), “superfluorescence” from ordered colloidal crystallites at cryogenic temperatures, and coherent single-photon emission . It has been readily observed that the charge-carriers can be manipulated in LHP nanomaterials through carrier multiplication, , phonon bottlenecks during hot carrier relaxation, − size-dependent Stokes shifts, , and down conversion using transition metal and lanthanide dopants.…”