Ko Brian A, Berry Keith, Qin Zhaojun, Sokolov Alexei V, Hu Jonathan, Scully Marlan O, Bao Jiming, Zhang Zhenrong
Baylor University, Waco, Texas 76706, United States.
Texas A&M University, College Station, Texas 77843, United States.
ACS Appl Mater Interfaces. 2021 Dec 8;13(48):57075-57083. doi: 10.1021/acsami.1c14092. Epub 2021 Nov 19.
Two-dimensional organic-inorganic lead halide perovskites are generating great interest due to their optoelectronic characteristics such as high solar energy conversion efficiency and a tunable direct band gap in the visible regime. However, the presence of defect states within the two-dimensional crystal structure can affect these properties, resulting in changes to their band gap emission as well as the emergence of nonlinear optical phenomena. Here, we have investigated the effects of the presence of defect states on the nonlinear optical phenomena of the 2D hybrid perovskite (BA)(MA)PbBr. When two pulses, one narrowband pump pulse centered at 800 nm and one supercontinuum pulse with bandwidth from 800-1100 nm, are incident on a perovskite flake, degenerate four-wave mixing (FWM) occurs, with peaks corresponding to the energy levels of the defect states present within the crystal. The longer carrier lifetime of the defect state, in comparison to that of virtual transitions that take place in nonresonant FWM processes, allows for a larger population of electrons to be excited by the second pump photon, resulting in increased FWM signal at the defect energy levels. The quenching of the two-photon luminescence as flake thickness increases is also observed and attributed to the increased presence of defects within the flake at larger thicknesses. This technique shows the potential of detecting defect energy levels in crystals using FWM for a variety of optoelectronic applications.
二维有机-无机铅卤化物钙钛矿因其光电特性，如高太阳能转换效率和在可见光范围内可调的直接带隙，而备受关注。然而，二维晶体结构中缺陷态的存在会影响这些特性，导致其带隙发射发生变化以及非线性光学现象的出现。在此，我们研究了缺陷态的存在对二维杂化钙钛矿(BA)(MA)PbBr非线性光学现象的影响。当一个中心波长为800 nm的窄带泵浦脉冲和一个带宽为800 - 1100 nm的超连续脉冲入射到钙钛矿薄片上时，会发生简并四波混频(FWM)，其峰值对应于晶体中存在的缺陷态的能级。与非共振FWM过程中发生的虚拟跃迁相比，缺陷态的载流子寿命更长，这使得更多的电子能够被第二个泵浦光子激发，从而导致缺陷能级处的FWM信号增强。还观察到随着薄片厚度增加双光子发光的猝灭现象，并将其归因于较大厚度薄片中缺陷的增加。这种技术显示了利用FWM检测晶体中缺陷能级在各种光电应用中的潜力。
