Highly Enhanced Third-Harmonic Generation in 2D Perovskites at Excitonic Resonances

Abstract

Two-dimensional hybrid organic-inorganic Ruddlesden-Popper perovskites (RPPs) have attracted considerable attention due to their rich photonic and optoelectronic properties. The natural multi-quantum-well structure of 2D RPPs has been predicted to exhibit a large third-order nonlinearity. However, nonlinear optical studies on 2D RPPs have previously been conducted only on bulk polycrystalline samples, in which only weak third-harmonic generation (THG) has been observed. Here, we perform parametric nonlinear optical characterization of 2D perovskite nanosheets mechanically exfoliated from four different lead halide RPP single crystals, from which we observe ultrastrong THG with a maximum effective third-order susceptibility (χ) of 1.12 × 10 m V. A maximum conversion efficiency of 0.006% is attained, which is more than 5 orders of magnitude higher than previously reported values for 2D materials. The THG emission is resonantly enhanced at the excitonic band gap energy of the 2D RPP crystals and can be tuned from violet to red by selecting the RPP homologue with the requisite resonance. Due to signal depletion effects and phase-matching conditions, the strongest nonlinear response is achieved for thicknesses less than 100 nm.

Organic‐Inorganic Hybrid Perovskite Single Crystals: Crystallization, Molecular Structures, and Bandgap Engineering

“…also obtained (C 4 H 9 NH 3 ) 2 PbBr 4 (n=1), (C 4 H 9 NH 3 ) 2 PbI 4 (n=1), (C 4 H 9 NH 3 ) 2 (CH 3 NH 3 )Pb 2 I 7 (n=2), and (C 4 H 9 NH 3 ) 2 (CH 3 NH 3 ) 2 Pb 3 I 10 (n=3) (Figure b) through a STL method (for lead iodide R−P phases) or an AVC method (for lead bromide R−P phases). The THG emission intensity varies strongly with the thickness of the perovskite sheets due to signal depletion and phase‐matching conditions and the optimal thickness lies in the range of 22–61 nm for n=1 to 3 R‐P phases …”

2D Layered Materials: Synthesis, Nonlinear Optical Properties, and Device Applications

“…Meanwhile, other optical properties, including third‐harmonic generation, parametric process, and stimulated Brillouin scattering, have been also explored, which promotes the development of layered materials‐based nonlinear optics.…”

Giant and Tunable Optical Nonlinearity in Single‐Crystalline 2D Perovskites due to Excitonic and Plasma Effects

“…Feasibly, the weak van der Waals forces between the organic chains of adjacent layers, make it possible to exfoliate bulk 2D hybrid RPP crystals into thin sheets, which are interesting for both fundamental studies and potential applications. Indeed, it has recently been demonstrated that single‐crystalline butylammonium lead halide RPP nanosheets exhibit strong THG when pumping them with an IR laser at the three‐photon resonance of the 1s exciton . However, their NLO response under one‐photon‐resonant excitation has not yet been investigated.…”

“…Five centimeter‐sized, pure phase RPP single crystals with the general formula [(BA) 2 (MA) n ‐1 Pb n X 3 n +1 ] (where BA = butylammonium (C 4 H 9 NH 3 ), MA = methylammonium (CH 3 NH 3 ), X = I − or Br − , and n is the number of inorganic layers within each quantum well) were synthesized through a temperature‐programmed crystallization method (for iodide‐based RPPs) or an antisolvent vapor diffusion method (for bromide‐based RPPs) . The synthesized crystals are [(BA) 2 PbBr 4 ] ( n = 1), [(BA) 2 PbI 4 ] ( n = 1), [(BA) 2 (MA)Pb 2 I 7 ] ( n = 2), [(BA) 2 (MA) 2 Pb 3 I 10 ] ( n = 3), and [(BA) 2 (MA) 3 Pb 4 I 13 ] ( n = 4), hereafter denoted as Br n =1 , I n =1 , I n =2 , I n =3 , and I n =4 , respectively.…”