α‐SnF2: A UV Birefringent Material with Large Birefringence and Easy Crystal Growth

Abstract The simple binary fluoride α‐SnF 2 is shown to be an excellent birefringent material with outstanding birefringence, about 14 times that of MgF 2 . Furthermore, it exhibits a shorter UV cutoff edge and easy crystal growth at ambient temperature compared to YVO 4 and TiO 2 . A novel theoretical calculation mode was established to analyze the stereochemical‐activity lone‐pair (SCALP) contribution to the birefringence (SCB) based on the SCALP′s strength and arrangement, and it was found that the large birefringence of α‐SnF 2 mainly benefits from well‐aligned [SnF 5 ] polyhedra with a strong SCALP. The exploration of the α‐SnF 2 birefringent crystal points out the direction of the future search for excellent birefringent materials.