CO2 Pressure-Induced Self-Trapped Excitons in SrTiO3

With strong electron–phonon coupling, self-trapped excitons (STEs) are typically formed in perovskite materials, and radiative recombination of STEs can produce broadband emission with large Stokes shifts. STEs are essential to further improve the optoelectronic properties of materials. Surprisingly, 2D system is the edge case, with low even no self-trapping barriers, leading to effortless formation of STEs. In this work, 2D strontium titanate (SrTiO₃) with defects is prepared using supercritical carbon dioxide (SC CO₂) and its carrier transport and transition are studied. The appearance of wide photoinduced positive absorption signals in the femtosecond transient absorption spectra is direct evidence for the formation of STEs. The presence of STEs is further supported by the increased Stokes shift and full width at half maximum in the steady-state photoluminescence spectra.