Extremely Long Spin Lifetime of Light-Emitting States in Quasi-2D Perovskites through Orbit–Orbit Interaction

Abstract

This paper reports an extremely long spin relaxation time of optically polarized light-emitting states at room temperature in quasi-2D perovskites [(PEA)2(MA)4Pb5Br16 with n = 5], when the long-range orbit–orbit interaction between excited states is developed through orbital polarization. Our studies found that the quasi-2D perovskite [(PEA)2(MA)4Pb5Br16 with n = 5] demonstrates a long-range orbit–orbit interaction between excited states to conserve the spins of optically polarized light-emitting states, identified by the positive change on photoluminescence intensity (+ΔPL) in steady state upon switching the photoexcitation from linear to circular polarization. Meanwhile, the PL circular polarization (σ+σ+ – σ+σ–) can maintain in nanosecond under fixed photoexcitation (σ+). In contrast, the 2D/3D mixed perovskite (n > 5) shows a short-range orbit–orbit interaction between excited states through orbital magnetic dipoles, identified by the −ΔPL by switching from linear to circular photoexcitation. At the same time, the spin lifetime of light-emitting states becomes undetectable.

Identifying Photoinduced Dipolar Polarization and Orbit–Orbit Interaction between Excitons in Organic–Inorganic Hybrid Perovskites

“…Especially, we have developed a unique method to identify these two types of orbit-orbit interactions by using the positive and negative ΔJ sc or ΔPL while switching photoexcitation from linear to circular polarizations. [31][32][33] Here, we found that the exciton-exciton interaction occurs through orbital magnetic dipoles (i.e., spin dipoles), leading to magnetic-type orbit-orbit interaction between excitons in the MA x FA (1−x) PbI 3 perovskite devices. Specifically, a circularly polarized photoexcitation (σ + ) generates the samedirectional orbital magnetic dipoles between excitons, while a linearly polarized photoexcitation (the combination of σ + and σ − ) gives rise to opposite-directional orbital magnetic dipoles between excitons, as shown in Figure 5.…”

Nature of the different emissive states and strong exciton–phonon couplings in quasi-two-dimensional perovskites derived from phase-modulated two-photon micro-photoluminescence spectroscopy

“…Although there are some reports on underlying physical processes that govern PL in q-2D material, 3,[28][29][30] a systematic and unified description of the recombination mechanisms is lacking. In this regard, phase modulation in nonlinear spectroscopic techniques can provide valuable information about the different types of PL recombination mechanisms and particularly the PL contributions from different electronic states in semiconductor material and other photo-active systems.…”

Polarized Photoluminescence from Lead Halide Perovskites

“…[22,74,75] In this case, the degree of circular polarization is determined by the spin relaxation across the sublevels, which could occur on the time scale of nanoseconds and be comparable to the radiative transition in MAPbI 3 . [73,76,77] As shown in Figure 5c, the photoluminescence could become highly circularly polarized when the MAPbBr 3 thin film was excited with circularly polarized light. [74] The polarization P could be as high as 2% at the photon energy close to the optical bandgap, which was influenced by the competition between spin relaxation and radiative recombination processes.…”