Lead-Free Solid State Mechanochemical Synthesis of Cs2NaBi1- xFexCl6 Double Perovskite: Reduces Band Gap and Enhances Optical Properties

Rohini Udavant; Sachin Thawarkar; Sachin Rondiya; Ankita Shelke; Rahul Aher; Thalasseril G Ajithkumar; Russell W Cross; Nelson Y Dzade; Sandesh Jadkar

doi:10.1021/acs.inorgchem.2c04149

Lead-Free Solid State Mechanochemical Synthesis of Cs₂NaBi_{1- x}Fe_xCl₆ Double Perovskite: Reduces Band Gap and Enhances Optical Properties

Inorg Chem. 2023 Mar 27;62(12):4861-4871. doi: 10.1021/acs.inorgchem.2c04149. Epub 2023 Mar 15.

Authors

Rohini Udavant¹, Sachin Thawarkar¹, Sachin Rondiya², Ankita Shelke³, Rahul Aher⁴, Thalasseril G Ajithkumar³, Russell W Cross⁵, Nelson Y Dzade⁶, Sandesh Jadkar¹

Affiliations

¹ Department of Physics, Savitribai Phule Pune University, Pune 411007, Maharashtra, India.
² Department of Materials Engineering, Indian Institute of Science (IISc), Bengaluru 560012, Karnataka, India.
³ Physical and Materials Chemistry Division, CSIR-National Chemical Laboratory, Pune 411008, Maharashtra, India.
⁴ Department of Physics, Dr. Vishwanath Karad MIT-World Peace University, Kothrud, Pune 411038, Maharashtra, India.
⁵ School of Chemistry, Cardiff University, Main Building, Park Place, Cardiff CF10 3AT, U.K.
⁶ Department of Energy and Mineral Engineering, Pennsylvania State University, University Park, Pennsylvania 16802, United States.

PMID: 36920788
DOI: 10.1021/acs.inorgchem.2c04149

Abstract

Efficient and stable lead-free halide double perovskites (DPs) have attracted great attention for the future generation of electronic devices. Herein, we have developed a doping approach to incorporate Fe³⁺ ions into the Cs₂NaBiCl₆ crystal unit and reveal a crystallographic and optoelectronic study of the Cs₂NaBi_1-xFe_xCl₆ double perovskite. We report a simple solid-state mechanochemical method that has a solvent-free, one-step, green chemistry approach for the synthesis of Cs₂NaBi_1-xFe_xCl₆ phosphor. The analysis of powder X-ray diffraction (XRD) data determines the contraction of the lattice due to the incorporation of Fe³⁺ cations, and this effect is well supported by X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), Raman spectroscopy, and solid-state nuclear magnetic resonance spectroscopy (ss-NMR). The band gap is reduced with increasing Fe content owing to the strong overlap of the Fe-3d orbitals with Cl-3p orbitals and shift of the valence band maxima (VBM) toward higher energies, as confirmed by ultraviolet photoelectron spectroscopy (UPS) and density functional theory (DFT) analyses. Photoluminescence (PL) studies of Cs₂NaBi_1-xFe_xCl₆ phosphors exhibit a large Stokes shift, broadband emission, and increased PL intensity more than ten times for 15% of Fe content phosphor with enhancement in the average decay lifetimes (up to 38 ns) compared to pristine Cs₂NaBiCl₆ DP. These results indicate that the transition of dark self-trapping of excitons (STEs) into bright STEs enhances yellow emission. XRD, UV, and thermo-gravimetric analysis (TGA) confirmed that the Cs₂NaB_1-xFe_xCl₆ DPs have good structural and thermal stabilities. Our findings indicate that the doping of Fe³⁺ cations into the Cs₂NaBiCl₆ lattice is a constructive strategy to enhance significantly the optoelectronic properties of these phosphors.