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

The simple binary fluoride α‐SnF2 is shown to be an excellent birefringent material with outstanding birefringence, about 14 times that of MgF2. Furthermore, it exhibits a shorter UV cutoff edge and easy crystal growth at ambient temperature compared to YVO4 and TiO2. 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‐SnF2 mainly benefits from well‐aligned [SnF5] polyhedra with a strong SCALP. The exploration of the α‐SnF2 birefringent crystal points out the direction of the future search for excellent birefringent materials. A simple binary fluoride α‐SnF2 crystal is a promising excellent UV birefringent material with outstanding birefringence, about 14 times that of MgF2, and exhibits a short UV cutoff edge and easy crystal growth.