Deep-ultraviolet (deep-UV, wavelength below 200 nm) coherent light plays an important role in a number of advanced scientific instruments. KBe₂BO₃F₂(KBBF) is the benchmark deep-UV NLO material, but it contains highly toxic beryllium and suffers a strong layering tendency, hindering its commercial applications.

Recent studies led by Prof. LUO Junhua and ZHAO Sangen from Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences obtained a new beryllium-freedeep-UVNLO material,K₃Ba₃Li₂Al₄B₆O₂₀F(KBLABF), by the substitution of toxic Be for Al & Li elements.KBLABFpreserves the double-layered structure of the notableSr₂Be₂B₂O₇(Nature,373, 322，1995).

In the structure of KBLABF, the[Li₂Al₄B₆O₂₀F]_∞double-layersmaintains the favorable arrangement of the NLO-active[BO₃]^3-groups in the structures of KBBF andSr₂Be₂B₂O₇, thereby preserving the desirable optical propeties of the latter:adeep-UVtransparent window, a powder SHG response (1.5 × KDP) comparable to that of KBBF, and phase-matchability.Furthermore,the[Li₂Al₄B₆O₂₀F]_∞double-layersare tightly bridged viaBa―O bonds.

As a result, KBLABF exhibits no layering growth tendency, which is confirmed by the as-grown KBLABF single crystal with athickness of about 8 mm in thecdirection. More importantly,KBLABFeliminates the structural instability ofSr₂Be₂B₂O₇, which is confirmed by the small structuralconverge factor,obtainment of large-sizedKBLABFsingle crytal, andphonon dispersioncalculations (byco-authorsProf. LIN Zheshuai et al from Technical Institute of Physics and Chemistry, Chinese Academy of Sciences).

These attributes makeKBLABFan attractive candidate for the next-generation deep-UV NLO materials. Moreover, the substitution of Be for Al&Li in beryllium borates provides a new opportunity to design beryllium-free deep-UV NLO materials with good performance.

The study entitled “Designing a Beryllium-Free Deep-Ultraviolet Nonlinear Optical Material without a Structural Instability Problem” has been published inJ. Am. Chem. Soc.(2016, 138, 2961-2964).

The substitution of Be forAl&LifromSr₂Be₂B₂O₇led to aberyllium-freedeep-UVNLO material,K₃Ba₃Li₂Al₄B₆O₂₀F, without a structural instability problem (Image by Prof. LUO Junhua's group)