A<sub>3</sub>Te(Zn<sub>2</sub>Ge)Ge<sub>2</sub>O<sub>14</sub> (A = Sr, Ba, and Pb): New Langasite Mid-infrared Nonlinear Optical Materials by Rational Chemical Substitution
Kaichuang Chen, Chensheng Lin, Shengzi Zhang, Guang Peng, Yu Chen, Dan Zhao, Huixin Fan, Shunda Yang, Xin Wen, Min Luo, Zheshuai Lin, Ning Ye
Abstract
Mid-infrared (mid-IR) nonlinear optical (NLO) crystals with excellent comprehensive performances are urgently demanded in the laser technology field. Herein, a series of new langasite members, A3Te(Zn2Ge)Ge2O14 (A = Sr, Ba, and Pb), were designed and synthesized through a rational chemical substitution strategy with classic A3BC3D2O14 langasites as ideal prototypes. These crystals exhibited excellent mid-IR NLO properties including a large second harmonic generation (SHG) response (2.7, 3.2, 13.0 × KDP under 1064 nm and 0.11, 0.12, 0.54 × AGS under 2090 nm), a large band gap (4.03, 3.98, and 3.43 eV), and a wide transparency region from the ultraviolet (UV) to mid-IR region. Compared to those langasites with light D-site cations, the titled crystals highlighted the reduction of vibration frequency by the introduction of heavier Ge4+ cations, which helps extend the transparency range in the mid-IR region. Additionally, theoretical calculation results revealed the significant enhancement of the SHG effect by Pb2+ cations on the A-site. This work confirmed the feasibility of our chemical co-substitution strategy and enriched the langasites.