Fig. 6: Types of monomers and dimers formed in Y6 crystal.

Natural transition orbitals (NTOs) of the (a) twisted (M1) and (b) bent (M2) monomers and (c) the dimer formed from these two monomers. Here, E denotes the transition energy in eV, f represents the oscillator strength, λ is the eigenvalue of the NTO, and ∆µ signifies the dipole moment change in Debye for the S0 → S1 transition.