Enhancement of Birefringence in Borophosphate Pushing Phase-Matching into the Short-Wavelength Region

Wenbin Zhang; Junben Huang; Shujuan Han; Zhihua Yang; Shilie Pan

doi:10.1021/jacs.2c02310

Enhancement of Birefringence in Borophosphate Pushing Phase-Matching into the Short-Wavelength Region

J Am Chem Soc. 2022 May 25;144(20):9083-9090. doi: 10.1021/jacs.2c02310. Epub 2022 May 13.

Authors

Wenbin Zhang^{1

2}, Junben Huang¹, Shujuan Han^{1

2}, Zhihua Yang^{1

2}, Shilie Pan^{1

2}

Affiliations

¹ CAS Key Laboratory of Functional Materials and Devices for Special Environments, Xinjiang Technical Institute of Physics & Chemistry, CAS, Xinjiang Key Laboratory of Electronic Information Materials and Devices, 40-1 South Beijing Road, Urumqi 830011, China.
² Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China.

PMID: 35561005
DOI: 10.1021/jacs.2c02310

Abstract

Borophosphates are very known for the short ultraviolet (UV) cutoff edge and have become the promising UV and deep-UV functional crystals candidates; however, tetrahedral [PO₄] and [BO₄] groups own weak anisotropy of polarizability and are not conducive to large birefringence, which hinders their application in the short-wavelength region. Improving their birefringence without compromising the band gap is the main research objective. By introducing the excellent birefringent functional groups, such as [B₂O₅], [BO₂]_∞ chain, [B₂O_x(OH)_5-x], and so forth into borophosphates, seven borophosphates with improved birefringence were successfully synthesized (Δn > 0.05@532 nm). Remarkably, among them, the centimeter-sized crystal of Rb₃B₈PO₁₆ with a short deep-UV cutoff edge (175 nm) and large birefringence (Δn_(exp.) ∼ [email protected] nm) exhibits the shortest phase-matching wavelength (222 nm), which makes Rb₃B₈PO₁₆ a promising UV NLO crystal, while KB₆PO₁₀(OH)₄ with deep-UV cutoff edge features the largest birefringence (Δn_(exp.) ∼ 0.103@546 nm) in the reported borophosphate system, making KB₆PO₁₀(OH)₄ a promising deep-UV birefringent crystal. This study not only provides feasible strategies for increasing the birefringence of borophosphates but also pushes phase-matching into the short-wavelength region.