Anti-Stokes Ultraviolet Luminescence and Exciton Detrapping in the Two-Dimensional Perovskite (C6H5C2H4NH3)2PbCl4

Recently, it has been found that low-dimensional organometallic halide perovskites can be adopted as nonlinear monolayer emitters because of their efficient spontaneous anti-Stokes visual luminescence under visual or near-infrared laser excitation. Herein, we demonstrate a luminescence up-conversion process from the visible self-trapped exciton (STE) to an ultraviolet (UV) free exciton (FE) in the two-dimensional perovskite (C6H5C2H4NH3)2PbCl4 quantum wells excited by nanosecond pulse laser excitation. An ultraviolet 347 nm near-band-edge FE emission is obtained under the excitation of 579 nm dye laser at 10 K by a two-step, two-photon absorption process from the real intermediate exciton state. In addition, the decay rise time of higher-laying states of STE indicates the excitonic detrapping procedure could occur by the annihilation of phonons. Our results suggest that the low-dimensional halide perovskites with deformable structure are able to be applied in visible light-pumped UV-emitting devices.