High-pressure effects on the optical-absorption edge of $CdIn2S4$⁠, $MgIn2S4$⁠, and $MnIn2S4$ thiospinels

The effect of pressure on the optical-absorption edge of $CdIn2S4$⁠, $MgIn2S4$⁠, and $MnIn2S4$ thiospinels at room temperature is investigated up to $20GPa$⁠. The pressure dependence of their band gaps has been analyzed using Urbach’s rule. We have found that, within the pressure range of stability of the low-pressure spinel phase, the band gaps of $CdIn2S4$ and $MgIn2S4$ exhibit a linear blueshift with pressure, whereas the band gap of $MnIn2S4$ exhibits a pronounced nonlinear shift. In addition, an abrupt decrease of the band-gap energies occurs in the three compounds at pressures of 10, 8.5, and $7.2GPa$⁠, respectively. Beyond these pressures, the optical-absorption edge redshifts upon compression for the three studied thiospinels. All these results are discussed in terms of the electronic structure of each compound and their reported structural changes.