Generating Long-Lived Highly Excited Carriers in Undoped Perovskite Nanostructures by Two-Photon Upconversion.

Delayed electron emissions from undoped metal halide perovskite (CsPbBr3) nanostructures upon laser irradiation were observed to persist for a few nanoseconds. This was attributed to an extended lifetime of upconverted highly excited carriers. Experimental evidence suggests that the excitation of such states is through one-photon absorption by carriers and excitons. Theoretical work reveals that surface defects play an important role in modifying the band edge energies of the nanoparticles and thus allow the presence of these highly excited carrier states.