Tuning the Self-Trapped Emission: Reversible Transformation to 0D Copper Clusters Permits Bright Red Emission in Potassium and Rubidium Copper Bromides

Ternary
copper halides are promising materials for lighting and
displays, but red emission has yet to be reported among this class
of materials due to the difficulty in tuning the self-trapped exciton
(STE) emission. Here, we report lead-free hybrid organic–inorganic
ternary copper halides A6(DMSO)12­[Cu8Br13]­[Cu4Br4(OH)­(H2O)] (ACB-DMSO, A = K, Rb) synthesized as single crystals and
microcrystalline suspensions. These materials emit in the red portion
of the visible spectrum with a high photoluminescence quantum yield
(PLQY) of up to 75%. The changes in the emission spectrum are caused
by the solvent-induced transformation from the STE emitter A2CuBr3 to phosphorescent ACB-DMSO which reversibly transforms
blue-emitting 1D copper chains to red-emitting 0D copper clusters.
K6(DMSO)12­[Cu8Br13]­[Cu4Br4(OH)­(H2O)] (A
= K) can be used as the red-emitting phosphor for red light-emitting
didoes (LEDs), and by adding blue and green emitting cesium copper
halides, an all copper-based white LED with a high color rendering
index (CRI) over 97% is achieved.