Upconverted excitonic photoluminescence from a two-dimensional lead-halide perovskite

Anti-Stokes photoluminescence (AS-PL) is an interesting optical phenomenon that can cause laser cooling in certain semiconductors where incident laser photons are efficiently converted into photons with higher energy. The underlying upconversion mechanism can be used to realize optical refrigerators, but suited materials need to be developed for actual applications. Here, we investigate the AS-PL properties of a two-dimensional (2D) perovskite PEA₂PbI₄ single crystal and compare them with those of a three-dimensional (3D) perovskite MAPbI₃ single crystal. We find that, in the 2D perovskite PEA₂PbI₄, which has a large exciton binding energy, the free-exciton PL is dominant and that the measured upconversion gain spectra of both PEA₂PbI₄ and MAPbI₃ crystals are similar. The AS-PL process in these perovskite single crystals is discussed.