PbBe2B2O6: an ultraviolet nonlinear-optical crystal with unprecedented π–π interacting BeBO5 group

Abstract

π-Conjugated-group systems are fascinating and have been pursued for nonlinear materials owing to their superior optical and electronic properties, but are so far quite limited. Here, we report a new ultraviolet (UV) nonlinear-optical (NLO) beryllium borate crystal PbBe₂B₂O₆ that manifests an unprecedented π–π interacting BeBO₅ group, constructed by interconnected π-conjugated BeO₃ and BO₃ units. The PbBe₂B₂O₆ crystal has a short UV cutoff wavelength of 249 nm, phase-matching behavior in the whole transmission region from UV to IR light region (249–3166 nm), and remarkably the largest NLO effect (18.5 × KDP) among the π-conjugated UV NLO crystal materials. Theoretical calculation unravels that the highly NLO-active BeBO₅ group has strong π–π interactions. This work offers an innovative source of BeO₃-participating NLO materials and expands the frontier of NLO research.