High-efficiency red photoluminescence achieved by antimony doping in organic–inorganic halide (C11H24N2)2[InBr6][InBr4]

Abstract

Organic–inorganic metal halides (OIMHs) exhibit various crystal structures and strong broadband emission, showing enormous potential for solid-state lighting and displays. In this work, we report a new lead-free OIMH (C₁₁H₂₄N₂)₂[InBr₆][InBr₄], which adopts a typical zero dimensional (0D) structure with the inorganic polyhedra separated by the large organic cations. Different from the general 0D In-based OIMHs with single octahedral [InBr₆]³⁻ units, (C₁₁H₂₄N₂)₂[InBr₆][InBr₄] contains both [InBr₆]³⁻ octahedra and [InBr₄]⁻ tetrahedra. It shows a large optical bandgap of 3.95 eV and excellent ambient stability. In addition, Sb dopants can be included in the structure, and an obvious preference for substituting the In atoms in the [InBr₆]³⁻ octahedra has been determined by analyzing the related bond lengths and polyhedral distortion. (C₁₁H₂₄N₂)₂[InBr₆][InBr₄] exhibits a broadband red emission (660 nm) that is ascribed to self-trapped excitons (STEs) in octahedral [InBr₆]³⁻, and the photoluminescence quantum yield (PLQY) can be significantly enhanced from 8% to 61% upon Sb doping, mainly as a result of the extra photo-induced excitons from [SbBr₆]³⁻. Density functional calculations reveal the direct bandgap nature of (C₁₁H₂₄N₂)₂[InBr₆][InBr₄], which is transferred to an indirect band gap after Sb doping due to the formation of the intra-gap band. A white light-emitting diode (WLED) was fabricated by combining the red emissive (C₁₁H₂₄N₂)₂[InBr₆][InBr₄]:Sb³⁺ and commercial green and blue phosphors, exhibiting a high color-rendering index of 88.7. Our work reports high-efficiency red photoluminescence (PL) in this special 0D double-inorganic-unit system, and demonstrates its potential applications for solid-state lighting.