PNO: a promising deep-UV nonlinear optical material with the largest second harmonic generation effect

In this work, the polar tetrahedron [PN2O2] was revealed as a new deep-ultraviolet (deep-UV) nonlinear optically active unit. Accordingly, a thermodynamically stable compound (PNO) consisting of the polar [PN2O2] units was predicted and suggested as a promising candidate for deep-UV nonlinear optical (NLO) materials. Compared with other deep-UV materials known to date, PNO possesses the strongest second harmonic generation (SHG) coefficient (about 6 times that of KH₂PO₄ (KDP)). Moreover, its three-dimensional connectivity endows it with good mechanical and thermal properties. Therefore, PNO should be a new option for non-π-conjugated deep-UV NLO materials.