A General Principle for DUV NLO Materials: pi-Conjugated Confinement Enlarges Band Gap

摘要

Current nonlinear optical materials face a conventional limitation in the trade-off between the band gap and birefringence, especially in the deep UV spectral region. To circumvent this dilemma, we propose a general principle, pi-conjugated confinement, to partially decouple the interunit pi-conjugated interactions by the separation of non-pi-conjugated units. The goal is to further enlarge the band gap to a value larger than that of the singular pi-conjugated counterpart and to maintain a suitable density of pi-conjugated units to gain a large optical anisotropy. We reveal that pi-conjugated confinement is a shared structural feature for all DUV NLO materials known to date, and thus, it provides a novel and essential design criterion for future design synthesis. Guided by this principle, the carbonophosphates are predicted to be a new promising DUV candidate system. Sr3YPO4CO3(3) (1) and Na3XPO4CO3 (X=Ba, Sr, Ca, Mg, 2-5) exhibit not only greatly enhanced birefringence that is 3-24 times larger than that of singular phosphates but also enhanced band gaps that are 0.2-1.7 eV wider than those of singular carbonates.