KBe₂BO₃F₂ (KBBF) is the unique crystal that allows efficient generation of deep ultraviolet (DUV) light by direct frequency doubling. Its special two-dimensional(2D) layered structure is regarded as a typical prototype for designing new nonlinear optical (NLO) materials. The previous research has focused mainly on metal-containing KBBF-type UV materials. 

However, the higher requirements for practical ultraviolet (UV) NLO materials should be not only environmentally friendly but also energy efficient and economically inexpensive, which motivate the exploration for nontoxic, low-cost, and simple alternatives to metal-containing KBBF-type UV materials. 

In a new study published in Angew. Chem. Int. Ed., a group led by Prof. YE Ning from Fujian Institute of Research on the Structure of Matter (FJIRSM) of the Chinese Academy of Sciences, reported the first fluorosulfonic UV NLO material, C(NH₂)₃SO₃F, which is rationally designed by taking the KBe₂BO₃F₂ (KBBF) as the parent compound. 

Based on the structure of the KBe₂BO₃F₂ (KBBF), the researchers replaced inorganic (BO₃)^3- with organic C(NH₂)₃⁺ triangles and the substitution of BeO₃F with SO₃F^- tetrahedral. The designed compound C(NH₂)₃SO₃F inherited NLO-favorable layered structure of KBBF.  

Therefore, benefiting from the coplanar configuration of the C(NH₂)₃⁺ cationic groups, C(NH₂)₃SO₃F possesses large second-harmonic generation(SHG) response of 5×KH₂PO₄ (KDP) and moderate birefringence of 0.133@1064 nm. 

In addition, based on the first principles calculation, the researchers revealed that the shortest SHG phase - matching wavelength of C(NH₂)₃SO₃F can reach 200 nm. This finding indicated that C(NH₂)₃SO₃F may be applied to frequency-quadruple and -quintuple the Nd: YAG laser output, resulting in 266 and 213 nm coherent light. 

This study highlights the exploration of metal-free compounds as nontoxic and low-cost UV NLO materials will be a new research area. 

Schematic illustration of Structural evolution from KBBF to C(NH₂)₃SO₃F (Image by Prof. YE’s group)   

Contact: 

Prof. YE Ning  

Fujian Institute of Research on the Structure of Matter 

Chinese Academy of Sciences 

Email: nye@fjirsm.ac.cn