A challenging topic for tetrahedra-based deep-ultraviolet (deep-UV, wavelength λ < 200 nm) birefringence crystals is how to generate both large birefringence and high deep-UV transmittance. Edge-sharing tetrahedra can induce large structural distortion and thus could produce strong optical polarization anisotropy to realize the challenging topic, but edge-sharing tetrahedra frequently require extreme synthesis conditions to overcome large repulsion interaction between tetrahedra. Herein, under mild hydrothermal conditions, an α-Be3(H2O)2(PO4)2 crystal with edge-sharing BeO4 and its polymorph β-Be3(H2O)2(PO4)2 with common corner-sharing BeO4 were synthesized, both featuring a three-dimensional stable structure constructed by BeO4, BeO2(H2O)2, and PO4 tetrahedral units. Remarkably, α-Be3(H2O)2(PO4)2 manifests superior birefringence of 0.101 and high deep-UV transmittance of 167 nm, with the largest birefringent quality factor (BQF) of 0.75 among the known tetrahedra-based deep-UV materials. By contrast, β-Be3(H2O)2(PO4)2 manifests a small birefringence of 0.019 and 160 nm deep-UV transmittance, with only a mediocre BQF of 0.15. Further, computational investigations reveal that edge-sharing BeO4 makes a dominant contribution to the great birefringence. This study could push the synthesis of edge-sharing-tetrahedra materials and offers an alternative strategy toward designing high-performance tetrahedra-based deep-UV birefringence materials.
Luyong Zhang,Shibin Wang,Zhencheng Wu,Xueling Hou,Zhihua Yang,Fangfang Zhang,Shilie Pan
Tetrahedral oxygenated groups with large highest occupied molecular orbital-lowest unoccupied molecular orbital (H gaps such as [SO 4 ] are beneficial for deep ultraviolet (DUV) transmission but usually make against generating sufficient birefringence due to the small polarizability anisotropy. Thus, it is extremely difficult to obtain DUV transmission and large birefringence simultaneously in the search for DUV birefringent materials in sulfates. Herein, two new ammonium-rare earth metal sulfates, NH 4 Y(SO 4 ) 2 ·H 2 O and NH 4 YSO 4 F 2 , with DUV transmission are presented. Meanwhile, both exhibit greatly elevated birefringence through the involvement of NH 4 + units, compared to Y 2 (SO 4 ) 3 ·8H 2 O. Their optical properties are further investigated by theoretical calculations, and the effect of the introduction of NH 4 + into yttrium sulfate on optimizing the structures and properties is discussed. This work may provide a new perspective for further exploration of DUV birefringent materials in tetrahedral oxygenated group sulfates.
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