Structural transition and emission enhancement in vacancy-ordered halide double perovskite Cs2TeCl6 under pressure

The effect of pressure on the structural evolution, the enhancement of the photoluminescence intensity, and the optical bandgap of a vacancy-ordered double halide perovskite, Cs2TeCl6, is investigated systematically. We use synchrotron x-ray diffraction, Raman spectroscopy, optical bandgap, and photoluminescence measurements to explore the structural and optical properties of Cs2TeCl6 under pressure up to 30.0 GPa. We find that Cs2TeCl6 undergoes a structural transition from cubic Fm3¯m to monoclinic P21/n at very low pressure below 1.0 GPa. A significant increase in photoluminescence intensity and a rapid decrease in optical bandgap are observed, which are related to the octahedral distortion and structural transition. Interestingly, with increasing pressure, the sample regains its ambient Fm3¯m structure at around 3.4 GPa, maintaining the cubic phase up to 30.0 GPa. The sample undergoes an iso-structural transition at around 14.1 GPa pressure with a slight decrease in compressibility.