BaHgGeSe4 and SrHgGeSe4: Two New Hg-based Infrared Nonlinear Optical Materials

摘要： New practically usable IR nonlinear optical (NLO) crystals, especially those suitable for high-efficient pumping of the commercial 1 μm laser, are in urgent demand. However, only a few new IR NLO materials have been grown into bulk crystals and realized IR laser output during the past twenty years due to the extreme difficulty in achieving the coexistence of various strongly-correlated properties. In the manuscript, based on the bonding characteristics of the Hg element and an efficient screening strategy for high-performance new crystals, we identified two new Hg-based IR nonlinear (NLO) materials, BaHgGeSe4 and SrHgGeSe4. They crystallize in the polar space group Ama2 with the distorted HgSe4 and GeSe4 tetrahedra aligned parallelly. They exhibit exceptional balance among all the preferred properties for practical applications, especially for high-efficient pumping of the commercial 1 μm laser: Their large band gap (~2.5 eV) can avoid the two-photon absorption of 1 μm laser and increase the laser damage threshold; They are phase matchable with very strong NLO response (5×AgGaS2); They can cover both the 3-5 μm and 8-12 μm atmospheric windows. Moreover, they melt congruently, which indicate that bulk crystals can be obtained by the Bridgman method. Their overall properties outperform the traditional materials AgGaQ2 (Q = S, Se) in a large degree. Detailed structural analysis and calculations elucidate the crucial role of cations in regulating the packing of the anionic groups and that of the highly-polarizable HgSe4 in balancing optical properties.