Second-Harmonic-Generation Switching via Pressure-Suppressed Dynamical Disorder
Dequan Jiang, Xingxing Jiang, Xue Zhang, Chen Li, Ke Liu, Yingying Ma, Hao-Ming Cheng, Tianyao Pei, Ting Bin Wen, Zheshuai Lin, Fangfei Li, Yonggang Wang
Abstract
Second-harmonic-generation (SHG) switching is an emerging phenomenon with potential applications in bistable storage and optical switches while also serving as a sensitive probe for inversion-symmetry. Temperature-induced disorder–order phase transition has been proven to be a rational design strategy for achieving SHG bi-state switching; however, pressure-sensitive SHG switching via a disorder–order structural transition mechanism is rarely reported and lacks sensitivity and cyclicity as practical switching materials. Herein, we demonstrate the pressure-induced “dynamical disorder–order” phase transition as an effective strategy for triggering SHG and SHG switching in NH 4 Cl. The “dynamical disorder–order” phase transition of NH 4 Cl occurring at as low as 1 GPa is confirmed by comprehensive in situ high-pressure XRD, molecular vibrational spectra, and Brillouin scattering spectra. The pressure-induced SHG is responsive to a wide excitation wavelength region (800–1500 nm), and the “off–on” switching is reversible for up to 50 cycles, setting a record for pressure-driven switching materials. It is worth noting that when pressure is further increased to 14 GPa, NH 4 Cl exhibits another SHG “on–off” switching, which makes it the first triplet SHG “off–on–off” switching material. Molecular dynamics simulations reveal the key role of N–H···Cl hydrogen bonding in the pressure-induced “dynamic disorder–order” mechanism. Finally, we verified that chemical pressure and physical pressure can jointly regulate the SHG switching behavior of NH 4 X (X = Cl, Br). The pressure-driven “dynamic disorder–order” transition mechanism sheds light on the rational design of multistable SHG switching materials for photoswitches and information storage.