Highly emissive and color-tunable copper-based halide composites for bright white light-emitting diodes

Lead-free metal halides have gained considerable attention due to their excellent optoelectronic properties; however, the direct synthesis of white light sources remains a challenge for developing high-performance white light-emitting diodes (WLEDs). Herein, we synthesized all-inorganic copper-based ternary halides using a microwave method. Through a strategy of controlling the amount of cuprous iodide (CuI), two highly efficient light emitters, blue-emissive Cs3Cu2I5 and yellow-emissive CsCu2I3, can be obtained. The large Stokes-shifted broadband emission with a relatively long radiative lifetime is ascribed to the self-trapped exciton (STE) formation. The unique negative thermal quenching suggests that carrier transfer from more deeply trapped states to shallowly trapped states is beneficial for enhancing the STE emission. Moreover, with an increased amount of CuI, the as-synthesized Cs3Cu2I5@CsCu2I3 composites exhibit a series of stable cold/warm white-light emissions. The bright WLEDs ranging from cold-white (12810 K) to pure-white (6109 K) and warm-white (4149 K) are displayed by placing the Cs3Cu2I5@CsCu2I3 composite directly onto a commercial ultraviolet chip (310 nm), and an ultra-high color-rendering index (CRI) of 92 is achieved. The results imply that highly emissive and color-tunable copper-based halide composites open the door to explore their potential applications in next-generation solid-state lightings.