Charge transfer excitons and directional fluorescence of in-plane lateral MoSe₂-WSe₂ heterostructures

In this article, the linear and nonlinear optical properties of in-plane lateral MoSe₂-WSe₂ heterostructures are theoretically investigated. The polarization-dependent strongest optical absorption in one-photon absorption occurs in charge transfer excited states, where electrons transfer from WSe₂ to MoSe₂. This phenomenon is supported by the LUMO (lowest unoccupied molecular orbital) and HUMO (highest occupied molecular orbital) imaging obtained through scanning tunneling microscopy. The charge difference density and transition density matrix are used to interpret the electronic transitions, and these interpretations rely on the concept of transition density. The optical properties of two-photon absorption in its nonlinear optical process are significantly different from the excitation in one-photon absorption, where the strongest optical absorption is contributed from direct transition from the ground state to the final state without going through an intermediate excited state, due to the very large difference of permanent dipole moments between the excited and ground states. Our results also reveal directional fluorescence and physical mechanism of in-plane lateral MoSe₂-WSe₂ heterostructures. Our work can provide insights into the physical mechanism of the optical properties of in-plane lateral MoSe₂-WSe₂ heterostructures.