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.