The bandgap energy of materials determines their applications in various fields. However, their bandgap energy is too large for photovoltaic applications. In the present study, high pressure technique is employed to tune the structures, so as the bandgap energies of double perovskite M₃TeO₆ (M=Mn, Co, and Cu). The giant bandgap reduction of M₃TeO₆ double perovskites has been observed after high-pressure treatment. The synchrotron-based X-ray diffraction and Raman spectroscopy results reveal that their significant bandgap reduction accompanies a sequence of structural phase transitions, some of which are irreversible. Furthermore, the high-pressure phase with smaller bandgap energy turns out to be quenchable to ambient conditions, making them promising light-harvesting material for photovoltaic applications. The main mechanism of the bandgap reduction is the enhanced overlap between M²⁺ 3d and O^2- 2p electronic wave functions. The present results demonstrate that high-pressure can represent a green and efficient technique to tune the properties of multifunctional materials.
 

HIGH PRESSURE,BANDGAP ENERGY,phase transition