Tightly bonded excitons in chiral metal clusters for luminescent brilliance

Chiral metal clusters have promise for circularly polarized luminescent materials; however, the absence of a unified understanding of the emission mechanism causes challenges in designing high-efficiency lighting materials based on these clusters. These challenges primarily arise from their vast structural variability and intricate emissive states. In this study, we show the crucial roles of the exciton binding energy and electron‒phonon interactions in achieving high-efficiency phosphorescence. Through Cu doping in the Au₄ clusters and changing ligand substituents, we increase the exciton binding energies and reduce the electron‒phonon interactions; this results in a maximum 1.3-fold increase in the radiative recombination rate, a maximum 241.1-fold decrease in the nonradiative recombination rate, and ultimately a phosphorescence quantum yield of over 96% and circularly polarized luminescence in metal cluster crystals. A solution-processed circularly polarized light-emitting diode prototype exhibits an external quantum efficiency of 15.51% in green and a maximum dissymmetry factor |g_EL| of 7.6 × 10^-3. Our findings highlight the significance of designing metal clusters with optimized exciton binding energies and electron‒phonon interactions for enhanced optoelectronic performance, including in circularly polarized optoelectronics.