High-Efficiency Yellow-Green Emission via Isolated Band Self-Trapping Exciton in Copper Doped Potassium Iodide Single Crystal

Yellow-green emitters have emerged in full-color displays, solid-state lighting, and biosensors. Currently, the solid-state yellow-green emitting materials are typically obtained through rare-earth phosphors or AlGaInN semiconductors. However, they possess an inherent radiative transition, which presents challenges in terms of color gamut and emission efficiency. Here, a centimeter-level copper-doped potassium iodide (KI/Cu) single crystal with high-efficiency yellow-green light emission was synthesized using a low-temperature water solution method. The crystal shows a broadband emission, with its center peak located at 561 nm and a large Stokes shift calculated to be approximately 200 nm. The doped copper ions introduce an isolated energy band in the electronic structure of KI, resulting in strengthened self-trapping excitons and a photoluminescence quantum yield (PLQY) of 98.98%. Based on the crystal, a white light-emitting diode with a broadband spectrum was fabricated by coupling with a UV chip, which offers new insights for yellow-green light emitting devices and their applications.