Broad Two-Photon Up-Conversion Photoluminescence Realized by Locally Polarized Heterostructures in 2D Perovskite

Organic-inorganic hybrid perovskites have demonstrated interesting infrared-to-visible up-conversion light-emitting properties from intrinsic excitons through multiphoton absorption. This paper reports a new approach to develop a broad two-photon up-conversion photoluminescence (PL) by using locally polarized heterostructure two-dimensional (2D) perovskites [(PEA(2)PbI(4))(1-x):(PEA(2)SnI(4))(x)] prepared by mixing Pb and Sn perovskite precursor solutions (PEA(2)PbI(4) and PEA(2)SnI(4)). Under infrared 1030 nm laser excitation, a charge-transfer exciton relative broad PL is observed with the peak position located at 670 and 660 nm, respectively, when PEA(2)PbI(4) and PEA(2)SnI(4) are alternatively serving as host and guest components in 2D perovskite heterostructures [(PEA(2)PbI(4))(0.95):(PEA(2)SnI(4))(0.05)] and [(PEA(2)SnI(4))(0.95):(PEA(2)PbI(4))(0.05)]. The transient absorption (TA) studies show that two-photon excitation quickly generates the charge-transfer excitons within 0.42 ps and slowly develops into a broad bleaching signal in 33 ps and lasting up to nanoseconds, forming metastable states ready for up-conversion light emission under two-photon excitation. Therefore, the charge-transfer excitons can be used as an artificial ability to achieve up-conversion light emission. Furthermore, polarization-dependent up-conversion PL studies reveal that charge-transfer excitons experience the orbit-orbit interaction through polarization heterostructures to form locally polarized heterostructures toward developing broad two-photon up-conversion light emission in 2D perovskites. Clearly, the locally polarized heterostructures provide a new design to develop multiphoton up-conversion light emission by forming virtual states functioning as two-photon energy coupling-assisted centers, leading to a large cross-section area for multiphoton absorption in organic-inorganic hybrid perovskites toward thin-film sensing applications.