Pressure Controls the Structure and Nonlinear Optical Properties of Piezochromic CdTeMoO₆

Abstract

Materials with excellent nonlinear optical properties, especially the second-harmonic-generation (SHG) ability that can double the frequency of a laser ω to 2ω, are greatly important to modern optical technology. Recently, a temperature-induced SHG “on–off” phenomenon has been reported in dozens of metal–organic complexes, which have emerged as candidates in advanced optoelectronic applications. As a counterpart to temperature, pressure is also expected to trigger a SHG “on–off” phenomenon; nevertheless, such material is relatively limited. Herein, we report the observation of a pressure-induced SHG “on–off” phenomenon accompanied by a structural phase transition and piezochromism in CdTeMoO6. Under ∼10 GPa compression, the material exhibits a sharp transition from the “SHG-on” state to the “SHG-off” state. Coupled with the SHG “on–off” phenomenon, a structural transition occurs from two-dimensional to three-dimensional due to the dramatic change in the coordination environments of Te4+ and Mo6+ from [TeO4] and [MoO4] tetrahedra to [TeO6] and [MoO6] octahedra, respectively. The suppression of stereoactive lone-pair electrons on Te4+ is considered to be responsible for the SHG-off state under high pressure. Piezochromism from colorless to black is also observed coupled with the SHG “on–off” phenomenon, which can be attributed to the hybridization between Mo 4d and O 2p orbitals. Moreover, we demonstrate that the “three-in-one” transition (structural transition, SHG on–off, and piezochromism) is irreversible at room temperature but reversible upon annealing at increased temperatures (230–350 °C) with SHG, lattice dimension and color returning to those of the initial state. All of these behaviors make CdTeMoO6 a maneuverable pressure- and temperature-regulated SHG switching material with pragmatic multifunctionality.

Pressure‐Driven Two‐Step Second‐Harmonic‐Generation Switching in BiOIO3

“…The strong overall SHG efficiency of BiOIO 3 ( � 12.5 × KDP) is mainly attributed to the alignment of the I 5 + lone-pair electrons. [12] Referring to the previous HP studies on the lone-pair electron dominated systems, [10,11] there are enough reasons to expect abundant changes of the SHG properties in BiOIO 3 under compression.…”

“…[10] Previously, we have observed the SHG "on-off" transition in the SHG-active CdMoTeO 6 by pressure-regulated lone-pair electrons. [11] Further exploration of this kind of materials has attracted our attention to a recently reported iodate BiOIO 3 , in which both the Bi 3 + and I 5 + cations contain the stereo-active lonepair electrons promising for achieving stepwise SHG switching under compression. [12] Herein, we report the experimental results on the SHG properties of BiOIO 3 based on both the in situ high-pressure (HP) powder and polarizationdependent single-crystal SHG measurements.…”

“…According to previous studies, pressure is generally considered to suppress the lone‐pair effect, and thus to influence the overall SHG property of materials [10] . Previously, we have observed the SHG “on‐off” transition in the SHG‐active CdMoTeO 6 by pressure‐regulated lone‐pair electrons [11] . Further exploration of this kind of materials has attracted our attention to a recently reported iodate BiOIO 3 , in which both the Bi 3+ and I 5+ cations contain the stereo‐active lone‐pair electrons promising for achieving stepwise SHG switching under compression [12] .…”

High-pressure bandgap engineering and amorphization in TiNb2O7 single crystals

“…Starting from 16.2 GPa, the sample experienced colour changes from colourless to yellow and finally to translucent dark yellow at 47.0 GPa, and this pressure induced colour change is reported in many other studies. 45,46 Upon decompression, the crystal colour returned to the initial colourlessness, indicating that the colour change is reversible. The colour we perceive in an object depends on the wavelength of light it transmits and reflects.…”

Tellurate polymorphs with high-performance nonlinear optical switch property and wide mid-IR transparency

“…[2][3][4][5] Among the various types of NLO switches, solid-state NLO switches based on second harmonic generation (SHG) show superiority in terms of stability, reversibility, and contrast. [6][7][8] Since SHG correlates strongly with the loss of the inversion center, it can be manipulated by symmetry breaking caused by external stimuli, such as temperature, 9 pressure, 10 and electric field. 11 Particularly, the temperature has been widely applied to initiate structural phase transitions accompanied by symmetry changes between the noncentrosymmetric and centrosymmetric phases, corresponding to the "SHG ON" and "SHG OFF" states, respectively.…”