Department of Chemistry, University of Southern California, Los Angeles, California 90089, United States.
Department of Chemistry, University of Houston, Houston, Texas 77204, United States.
ACS Appl Mater Interfaces. 2023 Apr 12;15(14):18006-18011. doi: 10.1021/acsami.2c20648. Epub 2023 Mar 28.
We report the growth and photophysical characterization of two polar hybrid lead halide phases, methylenedianiline lead iodide and bromide, (MDA)PbI and (MDA)PbBr, respectively. The phases crystallize in noncentrosymmetric space group 2, which produces a highly oriented molecular dipole moment that gives rise to second harmonic generation (SHG) upon excitation at 1064 nm. While both compositions are isostructural, the size dependence of the SHG signal suggests that the bromide exhibits a stronger phase-matching response whereas the iodide exhibits a significantly weaker non-phase-matching signal. Similarly, fluorescence from (MDA)PbBr is observed around 630 nm below 75 K whereas only very weak luminescence from (MDA)PbI can be seen. We attribute the contrasting optical properties to differences in the character of the halide sublattice and postulate that the increased polarizability of the iodide ions acts to screen the local dipole moment, effectively reducing the local electric field in the crystals.
我们报告了两种极性混合卤化铅相，即亚甲基二苯胺碘化铅和溴化铅（MDA）PbI 和（MDA）PbBr 的生长和光物理特性。这些相分别在非中心对称空间群 2 中结晶，产生高度定向的分子偶极矩，在 1064nm 激发下产生二次谐波产生（SHG）。虽然两种组成都是同构的，但 SHG 信号的尺寸依赖性表明溴化物表现出更强的相位匹配响应，而碘化物表现出明显较弱的非相位匹配信号。同样，在 75K 以下，（MDA）PbBr 发出约 630nm 的荧光，而（MDA）PbI 只能看到非常微弱的发光。我们将对比光学性质归因于卤化物亚晶格性质的差异，并假设碘化物离子的极化率增加会屏蔽局部偶极矩，从而有效地降低晶体中的局部电场。
