Deep-ultraviolet (DUV, λ< 200 nm) nonlinear optical (NLO) materials have become increasingly important because of their unique ability for deep-UV coherent light generation, which are of interest in laser micromachining, photochemical synthesis and many advanced scientific instruments e.g. deep-UV photoemission electron microscopy (DUV-PEEM), ultrahigh-resolution and angle-resolved photoemission  spectrometer (URPES and ARPES, respectively) and so forth. 

In a study published in Journal of the American Chemical Society,  the research group led by Prof. YE Ning from Fujian Institute of Research on the Structure of Matter (FJIRSM) of the Chinese Academy of Sciences (CAS) reported two novel noncentrosymmetric alkaline earth  fluorooxoborates, M2B10O14F6 (M = Ca, Sr) (CBOF and SBOF).  

These two fluorooxoborates showed not only remarkable stability against air and moisture. Besides, the thermodynamic analysis revealed that CBOF and SBOF are stable up to ~630℃, which show high thermal stability than alkali metal as well as ammonium DUV fluorooxoborates, such as NH4B4O6F (~300℃), RbB4O6F (452℃), CsB4O6F (609℃), KCsB8O12F2 (412℃), RbCsB8O12F2 (495℃).  

Powder SHG (PSHG) measurements under 1064 and 532 nm fundamental wave laser radiation revealed that they were phase-matchable in the visible and UV region and the SHG intensities of CBOF and SBOF were 2.3 and 2.5 times that ofKH2PO4(KDP) and ～0.4 times that of b-BaB2O4(BBO).  

UV/vis/NIR diffuse-reflectance spectra showed CBOF and SBOF exhibited a wide transparency and both of them had short UV cutoff edges below 200 nm.

Further theoretical investigations indicated that these two compounds had excellent linear and NLO properties, which were superior to those of  KBe2BO3F2 (KBBF).  

It is notable that the SHG phase-matching wavelength of CBOF and SBOF are predicted down to 169 and 171 nm, which are far shorter than that of most reported DUV materials. These properties made M2B10O14F6 (M = Ca, Sr) promising next-generation DUV NLO materials.