摘要: Nonlinear optical (NLO) crystals with efficient frequency conversion are essential for all-solid-state lasers, and exploring new second harmonic generation (SHG) enhancing strategy is crucial for the structure-property relationship research and application of NLO crystals. Conventional strategies focus on inducing parallel alignment of NLO active units. In this work, two new regulation means, i.e. bond polarization and flexible deformation, have been identified in rare earth carbonates REXCO3 (RE = La, Ce, Y; X = OH, F) with anionic motifs circular aligned through experimental characterization and first-principles calculations. They can promote the SHG effect in the form of electronic polarization and polyhedra distortion, respectively. Such regulation methods break the common acceptation that only carbonates aligning in a parallel pattern can effectively achieve the superposition of hyperpolarizabilities and result in considerable SHG effect. By realizing the synergistic effect of circular alignment and rare earth polyhedra, the polarizability and flexible stretching ability of the RE-O coordination bonds are effectively exerted in the designed structure, C2_La2O2CO3. This work unveils a new mechanism for SHG enhancement in rare earth carbonates and provides new insight for designing advanced NLO materials.