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Broadband Emission in Hybrid Organic–Inorganic Halides of Group 12 Metals

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journal contribution
posted on 28.12.2018, 18:20 by Rachel Roccanova, Matthew Houck, Aymen Yangui, Dan Han, Hongliang Shi, Yuntao Wu, Daniel T. Glatzhofer, Douglas R. Powell, Shiyou Chen, Houcem Fourati, Alain Lusson, Kamel Boukheddaden, Mao-Hua Du, Bayrammurad Saparov
We report syntheses, crystal and electronic structures, and characterization of three new hybrid organic–inorganic halides (R)­ZnBr3(DMSO), (R)2CdBr4·DMSO, and (R)­CdI3(DMSO) (where (R) = C6(CH3)5CH2N­(CH3)3, and DMSO = dimethyl sulfoxide). The compounds can be conveniently prepared as single crystals and bulk polycrystalline powders using a DMSO–methanol solvent system. On the basis of the single-crystal X-ray diffraction results carried out at room temperature and 100 K, all compounds have zero-dimensional (0D) crystal structures featuring alternating layers of bulky organic cations and molecular inorganic anions based on a tetrahedral coordination around group 12 metal cations. The presence of discrete molecular building blocks in the 0D structures results in localized charges and tunable room-temperature light emission, including white light for (R)­ZnBr3(DMSO), bluish-white light for (R)2CdBr4·DMSO, and green for (R)­CdI3(DMSO). The highest photoluminescence quantum yield (PLQY) value of 3.07% was measured for (R)­ZnBr3(DMSO), which emits cold white light based on the calculated correlated color temperature (CCT) of 11,044 K. All compounds exhibit fast photoluminescence lifetimes on the timescale of tens of nanoseconds, consistent with the fast luminescence decay observed in π-conjugated organic molecules. Temperature dependence photoluminescence study showed the appearance of additional peaks around 550 nm, resulting from the organic salt emission. Density functional theory calculations show that the incorporation of both the low-gap aromatic molecule R and the relatively electropositive Zn and Cd metals can lead to exciton localization at the aromatic molecular cations, which act as luminescence centers.