Suppressing electron–phonon coupling for narrow-band emitting Eu(II)-based perovskitoids

Narrow-band emitters are essential for solid-state lighting, displays, and single-photon sources. Here we design a family of lead-free Eu(II)-based hybrid perovskitoids with tightly face-shared connected [EuBr6]4– octahedrons, and the experimental and theoretical analyses verify that the electron-phonon coupling therein is suppressed via symmetrical structural parameters as confirmed by the low Huang–Rhys factor, and thus diminishes the homogeneous broadening of the emission bandwidths. Thus, TEtEuBr3 (TEt is Tetraethylammoniumwith) with symmetrical octahedrons shows ultra-narrow-band cyan emission (full width at half maximum ~36 nm) characterized by localized 5d-4f transition of Eu(II). The as-fabricated phosphor-converted light-emitting-diodes demonstrate low blue light hazard index and high color-rendering index of 96% in full-spectrum lighting technologies, moreover, they realize ultrahigh color gamut of ~115% Rec. 2020 as four-color display devices. We expect this strategy can be expanded to other narrow-band emitters for state-of-the-art optoelectronic applications. Europium halide perovskitoids are new class of lead-free emitters with high efficiency due to symmetry allowed 5d−4f transitions. Here the authors design europium bromides with narrow emission through suppressing electron-phonon coupling.