Tuning the optical properties of chiral two-dimensional perovskites by high pressure

Chiral two-dimensional perovskites are a class of low-dimensional perovskite materials with noncentrosymmetric structures. It combines the advantages of low-dimensional perovskites and chiral materials and thus can be used to produce nonlinear optical effects. Various optical properties of low-dimensional perovskites have been reported to be regulated by high-pressure technology. However, there are few reports on the high-pressure optical properties of chiral two-dimensional perovskites, especially the nonlinear optical effect under high pressure. The PL spectrum, absorption spectrum and second harmonic effect (SHG) of a high-pressure chiral two-dimensional perovskite material (R-, S-)ClPEA₂PbI₄ were studied by the diamond anvil cell technique. The results show that with increasing pressure, the PL spectral intensity of the material first increases to a peak of 1 GPa and then decreases gradually until it disappears at approximately 6 GPa, and the peak wavelength shifts from 507 nm to 568 nm. The high-pressure absorption spectra show that there is a sudden change in the absorption edge of the chiral perovskite at approximately 6 GPa, indicating the occurrence of a phase transition. Under high pressure, the intensity of the laser second harmonic signal decreases gradually with increasing pressure and significantly changes near a pressure of 6 GPa. These results show that high pressure is an effective way to regulate the optical properties of two-dimensional chiral perovskites, which provides a basis for their future applications in luminescence, near-infrared frequency conversion and other devices.