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Title: Synthesis, Crystal and Electronic Structures, and Optical Properties of (CH 3NH 3) 2CdX 4 (X = Cl, Br, I)

Here, we report the synthesis, crystal and electronic structures, as well as optical properties of the hybrid organic–inorganic compounds MA 2CdX 4 (MA = CH 3NH 3; X = Cl, Br, I). MA 2CdI 4 is a new compound, whereas, for MA 2CdCl 4 and MA 2CdBr 4, 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 MA 2CdX 4 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 MA 2CdCl 4 forms a 2D layered perovskite structure and has two structural transitions at 283 and 173 K. In contrast, MA 2CdBr 4 and MA 2CdI 4 adopt 0D K 2SO 4-derived crystal structures based on isolated CdX 4 tetrahedra and show no phase transitions down to 20 K. The contrasting crystal structures and chemical compositions in the MA 2CdX 4 family impact their air stabilities, investigated for the first time in this work; MA 2CdCl 4 is air-stable, whereas MA 2CdBr 4 and MA 2CdI 4 partially decompose when left inmore » air. Optical absorption measurements suggest that MA 2CdX 4 have large optical band gaps above 3.9 eV. Room temperature photoluminescence spectra of MA 2CdX 4 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 MA 2CdX 4 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 MA 2CdX 4. On the basis of our combined experimental and computational results, MA 2CdX 4 and related compounds may be of interest for white-light-emitting phosphors and scintillator applications.« less
Authors:
 [1] ; ORCiD logo [2] ;  [1] ; ORCiD logo [2] ;  [1] ; ORCiD logo [2] ; ORCiD logo [1]
  1. Univ. of Oklahoma, Norman, OK (United States)
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
Grant/Contract Number:
AC05-00OR22725
Type:
Accepted Manuscript
Journal Name:
Inorganic Chemistry
Additional Journal Information:
Journal Volume: 56; Journal Issue: 22; Journal ID: ISSN 0020-1669
Publisher:
American Chemical Society (ACS)
Research Org:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
OSTI Identifier:
1410200

Roccanova, Rachel, Ming, Wenmei, Whiteside, Vincent R., McGuire, Michael A., Sellers, Ian R., Du, Mao -Hua, and Saparov, Bayrammurad. Synthesis, Crystal and Electronic Structures, and Optical Properties of (CH3NH3)2CdX4 (X = Cl, Br, I). United States: N. p., Web. doi:10.1021/acs.inorgchem.7b01986.
Roccanova, Rachel, Ming, Wenmei, Whiteside, Vincent R., McGuire, Michael A., Sellers, Ian R., Du, Mao -Hua, & Saparov, Bayrammurad. Synthesis, Crystal and Electronic Structures, and Optical Properties of (CH3NH3)2CdX4 (X = Cl, Br, I). United States. doi:10.1021/acs.inorgchem.7b01986.
Roccanova, Rachel, Ming, Wenmei, Whiteside, Vincent R., McGuire, Michael A., Sellers, Ian R., Du, Mao -Hua, and Saparov, Bayrammurad. 2017. "Synthesis, Crystal and Electronic Structures, and Optical Properties of (CH3NH3)2CdX4 (X = Cl, Br, I)". United States. doi:10.1021/acs.inorgchem.7b01986. https://www.osti.gov/servlets/purl/1410200.
@article{osti_1410200,
title = {Synthesis, Crystal and Electronic Structures, and Optical Properties of (CH3NH3)2CdX4 (X = Cl, Br, I)},
author = {Roccanova, Rachel and Ming, Wenmei and Whiteside, Vincent R. and McGuire, Michael A. and Sellers, Ian R. and Du, Mao -Hua and Saparov, Bayrammurad},
abstractNote = {Here, we report the synthesis, crystal and electronic structures, as well as optical properties of the hybrid organic–inorganic compounds MA2CdX4 (MA = CH3NH3; X = Cl, Br, I). MA2CdI4 is a new compound, whereas, for MA2CdCl4 and MA2CdBr4, 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 MA2CdX4 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 MA2CdCl4 forms a 2D layered perovskite structure and has two structural transitions at 283 and 173 K. In contrast, MA2CdBr4 and MA2CdI4 adopt 0D K2SO4-derived crystal structures based on isolated CdX4 tetrahedra and show no phase transitions down to 20 K. The contrasting crystal structures and chemical compositions in the MA2CdX4 family impact their air stabilities, investigated for the first time in this work; MA2CdCl4 is air-stable, whereas MA2CdBr4 and MA2CdI4 partially decompose when left in air. Optical absorption measurements suggest that MA2CdX4 have large optical band gaps above 3.9 eV. Room temperature photoluminescence spectra of MA2CdX4 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 MA2CdX4 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 MA2CdX4. On the basis of our combined experimental and computational results, MA2CdX4 and related compounds may be of interest for white-light-emitting phosphors and scintillator applications.},
doi = {10.1021/acs.inorgchem.7b01986},
journal = {Inorganic Chemistry},
number = 22,
volume = 56,
place = {United States},
year = {2017},
month = {11}
}