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Li<sub>3</sub>La<sub>2</sub>(BO<sub>3</sub>)<sub>3</sub> and Li<sub>1.75</sub>Na<sub>1.25</sub>La<sub>2</sub>(BO<sub>3</sub>)<sub>3</sub>: A Great Enhancement in Birefringence Induced by Optimal Arrangement of π-Conjugated [BO<sub>3</sub>] Units

DOI

24

Citations

57

References

2021

Year

Xuping Shi, Wenbin Zhang, Wenbing Cai, Shujuan Han, Zhihua Yang, Shilie Pan
Inorganic Chemistry

Abstract

In virtue of the essential role in controlling polarized light, outstanding ultraviolet (UV) and deep-ultraviolet (DUV) birefringent crystals are imperative in many advanced optical instruments. To design the UV and DUV crystals with large birefringence, we paid more attention to combining the excellent gene, π-conjugated [BO<sub>3</sub>] unit and metal cations beneficial to blue-shift the cutoff edge; finally, two rare-earth borates Li<sub>3</sub>La<sub>2</sub>(BO<sub>3</sub>)<sub>3</sub> and Li<sub>1.75</sub>Na<sub>1.25</sub>La<sub>2</sub>(BO<sub>3</sub>)<sub>3</sub> have been synthesized using the high-temperature solution method. Compared with Na<sub>3</sub>La<sub>2</sub>(BO<sub>3</sub>)<sub>3</sub>, Li<sub>3</sub>La<sub>2</sub>(BO<sub>3</sub>)<sub>3</sub> and Li<sub>1.75</sub>Na<sub>1.25</sub>La<sub>2</sub>(BO<sub>3</sub>)<sub>3</sub> are isostructural, and the isolated [BO<sub>3</sub>] units are arranged nearly parallel to each other in the structure, which is conducive to generating a larger birefringence. The structural comparison between the two crystals and Na<sub>3</sub>La<sub>2</sub>(BO<sub>3</sub>)<sub>3</sub> indicates that the various coordination environments of alkali metal cations play an important role in the evolution of the crystal structure from Li<sub>3</sub>La<sub>2</sub>(BO<sub>3</sub>)<sub>3</sub> and Li<sub>1.75</sub>Na<sub>1.25</sub>La<sub>2</sub>(BO<sub>3</sub>)<sub>3</sub> to Na<sub>3</sub>La<sub>2</sub>(BO<sub>3</sub>)<sub>3</sub>. This work can contribute to a better understanding of the enhancement in birefringence from Na<sub>3</sub>La<sub>2</sub>(BO<sub>3</sub>)<sub>3</sub> (0.023 @ 1064 nm) to Li<sub>3</sub>La<sub>2</sub>(BO<sub>3</sub>)<sub>3</sub> (0.078 @ 1064 nm) with the perspective of structure-property relationships. Meanwhile, the two title crystals possess the DUV cutoff edge (<190 nm), suggesting that they can be applied as the DUV birefringent crystals.

References

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