Dielectric effects, crystal field, and shape anisotropy tuning of the exciton fine structure of halide perovskite nanocrystals

Exciton Fine Structure of CsPbCl3 Nanocrystals: An Interplay of Electron–Hole Exchange Interaction, Crystal Structure, Shape Anisotropy, and Dielectric Mismatch

“…Following the calculations, the EFS can be addressed through the set of eqs S23 and S24 for any size, shape (i.e., anisotropy level), and dielectric mismatch configurations in the cubic (O h ) and tetragonal (D 4h ) crystal phases. In agreement with previous studies 31,56,67,68 the inspection of eq S23 shows that, in halide perovskite NCs with tetragonal lattice structure, both SR and LR contributions participate in the singlet (dark state)−triplet (bright state) and intratriplet (intrabright states) splitting with comparable strength. The shape distortion and dielectric discontinuity play roles in the form of weighting coefficients that modulate the amplitude of the LR Hamiltonian unperturbed eigenenergies (cubic shape, no dielectric contrast).…”

“…Due to the influence of several parameters on the NC EFS (absolute size, anisotropy level, nature of the dielectric environment), drawing a comparison between the existing compounds should be made with great caution. As stressed in a recent theoretical work, Δ BD is especially sensitive to the dielectric mismatch and almost insensitive to the shape anisotropy, whereas Δ BB has schematically the opposite behavior . In that respect, a good starting point for discussion consists of investigating a reference situation allowing comparison.…”

“…Then the EFS is theoretically modeled including the short-range (SR) and long-range (LR) contributions of the e-h EI within an approach comparable to the one developed in bromide-based NCs. , In the model, the electron–hole Coulomb interaction potential serving to express the LR term is evaluated in the image charge formalism, which allows one to describe in an extensive manner the effects of dielectric confinement in the actual parallelepiped NC geometry. Following the calculations, the EFS can be addressed through the set of eqs S23 and S24 for any size, shape (i.e., anisotropy level), and dielectric mismatch configurations in the cubic ( O h ) and tetragonal ( D 4 h ) crystal phases.…”

“…As stressed in a recent theoretical work, Δ BD is especially sensitive to the dielectric mismatch and almost insensitive to the shape anisotropy, whereas Δ BB has schematically the opposite behavior. 67 In that respect, a good starting point for discussion consists of investigating a reference situation allowing comparison. The latter is defined as the weak confinement limit of excitons (i.e., large NCs with edge lengths, L, such that L ≫ a X ) in NCs of isotropic shape and in the absence of dielectric mismatch.…”