NH4PO3HCH3 and NH4PO3CH2NH3: Two Phosphate Derivatives with Deep-UV Cutoff Edges and Moderate Birefringence

To maintain moderate birefringent properties without compromising the wide optical transmittance window characteristic of phosphate materials, a crucial approach focuses on designing innovative functional units with great performance. This research has demonstrated that [PO3HCH3] and [PO3CH2NH3] units serve as effective birefringent-active components in the DUV regions. This study successfully prepared two novel crystalline materials, NH4PO3HCH3 and NH4PO3CH2NH3, which demonstrated both deep-UV transparency and moderate birefringence. These properties exceed those of conventional MgF2 crystals and the majority of known phosphate compounds in the DUV region. Computational investigations indicate that the observed birefringence is from the [PO3HCH3] and [PO3CH2NH3] building blocks, highlighting the potential of tetrahedral coordination environment engineering as a viable strategy for developing new optical functional units.