Dielectric confinement effect on excitons in ${\mathrm{PbI}}_4$-based layered semiconductors

By varying the dielectric environment in new ${\mathrm{PbI}}_4$-based layer-type perovskite compounds, we have demonstrated directly the contribution by dielectric confinement to the exciton binding energy in three such ‘‘natural-quantum-well’’ semiconductors. With different dielectric environment, exciton binding energies of 320, 220, and 170 meV have been observed, dominated by the dielectric confinement. In terms of the conventional size-related electronic confinement, two of the materials represent monolayer ${\mathrm{PbI}}_4$ quantum wells while the third corresponds to a bilayer case, with a corresponding reduction in the electronic confinement. From theory, including the dielectric confinement effect, the effective mass of the exciton in a ${\mathrm{PbI}}_4$-based dielectric quantum well has been determined to be 0.09${\mathit{m}}_{\mathit{e}}$; the corresponding quasi-two-dimensional exciton Bohr radii were 15.5, 17.0, and 20.5 Å for the three cases, respectively.