Title: Organic hybrid tetranuclear clusteroluminogens: Blue-light-excitable LED with ultrahigh luminous efficacy

The development of highly emissive luminescent materials is vital for future light-emitting diodes, display, and scintillation applications. A series of novel organic hybrid metal halide clusters are presented here, that is, non-emission (C4H12N2)3(NH4)4Cd4Cl18 (namely, 1), pink-emission (C4H12N2)3(NH4)4Mn4Cl18 (namely, 2) and 1–2 alloy (namely, Mn-1). The crystal structure of alloy compound provides a clear insight for the Mn(II) effect. Mn(II) alloying in the host lattice successfully induces large octahedral distortion, hybrid of d/p orbital and lower local symmetry resulting in a breaking d-d forbidden transition. The intense blue light absorption and high PLQY (92.6 %) inspire us to assemble Mn-1 as a blue-light-excited white light-emitting diode (WLED). The WLED has a minimized trade-off among luminous efficacy (182 lm/W), color-rendering index (82) and CCT (4536 K), which is achieved by the trichromatic combination (blue light chip, green (Ba, Sr)2SiO4:Eu2+, red Mn-1) and the red emission edge below 700 nm. The luminous efficacy of 182 lm/W is the highest among the previous WLEDs based on the lead-free metal halides, comparable to the market standard (185 lm/W) in 2020 set by The United States Department of Energy. In addition, the water-soluble Mn-1 further gives potential applications in X-ray scintillators, luminescent ceramics, flexible film and luminescent imaging agents. The discovery of tetranuclear metal halide clusters establishes a new strategy for constructing promising emissive materials.