A deep ultraviolet transparent birefringent monofluorophosphate: Cd2.5(NH4)2(PO3F)3Cl ⋅ 2H2O

Abstract Herein, we report a new monoclinic, Cd 2.5 (NH 4 ) 2 (PO 3 F) 3 Cl ⋅ 2H 2 O (CNPFC, cadmium ammonium monofluorophosphate chloride dihydrate), featuring a [Cd 3 P 2 O 12 ClF 2 ] ∞ double‐layered structure. CNPFC is DUV transparent, exhibits a quite large laser induced damage threshold (1.33×KDP) and emits a purple fluorescence at 410 nm. On an as‐synthesized (100)‐single crystal plane, the Δ n obv. (100)= n c – n b =0.012 is measured at 546 nm, which is consistent with the theoretical calculated 0.017. The birefringence of CNPFC is theoretically calculated to be Δ n cal. = n Z – n X =0.035. We further demonstrate that the diverse coordination environments and inter‐unit linkages of the Cd‐centered polyhedra as well as different hydrogen bonding interactions give rise to an interesting structural relationship among three related compounds.