Crystal Growth, Structure and Optical Properties of (NH ₄ ) ₂ Mg(SO ₄ ) ₂ ·6H ₂ O: A Crystal With a Wide Deep Ultraviolet Window

ABSTRACT Optical crystals with wide bandgap for deep ultraviolet (DUV) range are pivotal for the modern laser technologies, particularly in the field of solid‐state lasers. In this work, a DUV transparent magnesium‐ammonium sulfate (NH 4 ) 2 Mg(SO 4 ) 2 ·6H 2 O is successfully obtained through an aqueous solution evaporation method. It crystallizes in P 2 1 / c space group with cell parameters of a = 6.1940(11) Å, b = 12.582(2) Å, c = 9.3105(16) Å, and β = 107.095(5) °. Based on centimeter‐scale crystals, transmission spectra reveals that the crystal exhibits high transmittance in the range of 300–3000 nm with a DUV cutoff edge at 190 nm. This excellent DUV transparency is attributed to the rigid [SO 4 ] tetrahedra, a structural unit well‐established for its favorable contribution to a large bandgap. Meanwhile, the birefringence measurement indicates that the maximum refractive index difference of this compound is [email protected] nm. This study introduces a promising optical crystal with a short cut‐off edge and enriches the functional properties research of the sulfate family.