Roccanova Rachel, Ming Wenmei, Whiteside Vincent R, McGuire Michael A, Sellers Ian R, Du Mao-Hua, Saparov Bayrammurad
Department of Chemistry and Biochemistry, University of Oklahoma , 101 Stephenson Parkway, Norman, Oklahoma 73019, United States.
Materials Science and Technology Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.
Inorg Chem. 2017 Nov 20;56(22):13878-13888. doi: 10.1021/acs.inorgchem.7b01986. Epub 2017 Nov 2.
We report the synthesis, crystal and electronic structures, as well as optical properties of the hybrid organic-inorganic compounds MACdX (MA = CHNH; X = Cl, Br, I). MACdI is a new compound, whereas, for MACdCl and MACdBr, structural investigations have already been conducted but electronic structures and optical properties are reported here for the first time. Single crystals were grown through slow evaporation of MACdX solutions with optimized conditions yielding mm-sized colorless (X = Cl, Br) and pale yellow (X = I) crystals. Single crystal and variable temperature powder X-ray diffraction measurements suggest that MACdCl forms a 2D layered perovskite structure and has two structural transitions at 283 and 173 K. In contrast, MACdBr and MACdI adopt 0D KSO-derived crystal structures based on isolated CdX tetrahedra and show no phase transitions down to 20 K. The contrasting crystal structures and chemical compositions in the MACdX family impact their air stabilities, investigated for the first time in this work; MACdCl is air-stable, whereas MACdBr and MACdI partially decompose when left in air. Optical absorption measurements suggest that MACdX have large optical band gaps above 3.9 eV. Room temperature photoluminescence spectra of MACdX yield broad peaks in the 375-955 nm range with full width at half-maximum values up to 208 nm. These PL peaks are tentatively assigned to self-trapped excitons in MACdX following the crystal and electronic structure considerations. The bands around the Fermi level have small dispersions, which is indicative of high charge localization with significant exciton binding energies in MACdX. On the basis of our combined experimental and computational results, MACdX and related compounds may be of interest for white-light-emitting phosphors and scintillator applications.
我们报道了有机-无机杂化化合物MACdX（MA = CHNH；X = Cl、Br、I）的合成、晶体结构和电子结构以及光学性质。MACdI是一种新化合物，而对于MACdCl和MACdBr，此前已进行过结构研究，但本文首次报道其电子结构和光学性质。通过在优化条件下缓慢蒸发MACdX溶液生长出单晶，得到毫米尺寸的无色晶体（X = Cl、Br）和浅黄色晶体（X = I）。单晶和变温粉末X射线衍射测量表明，MACdCl形成二维层状钙钛矿结构，在283 K和173 K有两个结构转变。相比之下，MACdBr和MACdI采用基于孤立CdX四面体的零维KSO衍生晶体结构，在20 K以下无相变。MACdX家族中截然不同的晶体结构和化学组成影响其空气稳定性，本文首次对此进行研究；MACdCl在空气中稳定，而MACdBr和MACdI暴露在空气中会部分分解。光吸收测量表明，MACdX具有大于3.9 eV的大光学带隙。MACdX的室温光致发光光谱在375 - 955 nm范围内产生宽峰，半高宽值高达208 nm。根据晶体结构和电子结构的考虑，这些PL峰初步归因于MACdX中的自陷激子。费米能级附近的能带色散较小，这表明MACdX中电荷高度局域化，激子结合能较大。基于我们的实验和计算结果，MACdX及相关化合物可能在白光发光磷光体和闪烁体应用中具有吸引力。
