K(NH 4 )Zn 2 (PO 4 ) 2 : a Beryllium-Free Sr 2 Be 2 B 2 O 7 Derivative with Enhanced Interlayer Connectivity.

A novel zinc phosphate derivative of Sr 2 Be 2 B 2 O 7 (SBBO), K(NH 4 )Zn 2 (PO 4 ) 2 (KNZP), featuring [Zn 2 P 2 O 8 ] ∞ 2- double layers akin to the [Be 2 B 2 O 7 ] ∞ 4- layers in SBBO, was successfully synthesized via a moderate hydrothermal method. Through the substitution of BeO 4 and BO 3 with ZnO 4 and PO 4 , the issue of toxicity has been effectively resolved, while the enhanced interlayer interactions facilitated by covalent and hydrogen bonding in KNZP overcome the inherent structural instability. Notably, KNZP exhibits a wide transparent window and a moderate second-harmonic generation (SHG) intensity, reaching 0.7 times that of KH 2 PO 4 (KDP), rendering it type-I phase-matchable, indicating that it is a promising UV nonlinear optical (NLO) material.