Dimensionality Engineering of Fluorozirconium Phosphates for Deep-UV-Transparent Crystals with Enhanced Second-Harmonic Generation and Birefringence

Phosphate crystals have attracted significant interest as platforms for deep-ultraviolet (deep-UV) optical materials, attributable to their rich structural chemistry and tunable optical properties. However, simultaneously achieving strong second-harmonic generation (SHG) and enhanced birefringence in phosphate systems remains a formidable challenge. Herein, through a dimensionality-engineering strategy, we report five deep-UV transparent fluorozirconium phosphate compounds, including the three-dimensional (3D) ZrPO 4 F ( I ), two-dimensional (2D) Zr(H 2 PO 4 )(HPO 4 )F·3H 2 O ( II ) and (NH 4 ) 4 Zr 4 (HPO 4 ) 2 (PO 4 ) 4 F 4 ( III ), as well as the one-dimensional (1D) Rb 2.9 (NH 4 ) 3.1 Zr 4 (H 2 PO 4 )F 21 ( IV ) and Rb 4.2 (NH 4 ) 3.8 Zr 4 (PO 4 ) 2 F 18 ( V ). These compounds exhibit clear dimension-dependent optical properties, with reduced dimensionality leading to enhanced SHG responses and larger birefringence. Notably, the fluorine-rich 1D compounds display the strongest SHG efficiency (up to 2.1 × KDP) and the largest birefringence (0.053 @ 550 nm) within the series. Structure–property analyses reveal that decreasing the structural dimensionality promotes increased local distortion of Zr-centered polyhedra and more uniform dipole alignment, thereby amplifying both SHG and birefringence. This work establishes dimensionality engineering of fluorozirconium phosphates as an effective strategy for fine-tuning key optical properties while maintaining deep-UV transparency.