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

Abstract

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.