Insights into electronic transitions and coordination chemistry of cesium copper (I) iodide metal halides for yellow light emitting diodes

Inorganic phosphors are in high demand because these materials are widely used in modern technologies such as solid-state lighting, semiconductors lasers, luminescent solar concentrators, and display technologies including LCD and LED screens. Herein, we implemented a simple anti-solvent crystallization protocol using CsI and CuI dissolved in DMSO to synthesize CsCu 2 I 3 phosphors exhibiting a broadband yellow emission and a large Stokes shift. The electronic transitions in CsCu 2 I 3 were analyzed by DFT band structure and density of states calculations. The novelty of this study lies in integrating classical inorganic chemistry concepts, such as Fajans’ rules and the nephelauxetic effect, with modern computational approaches (DFT and Bader charge analysis) to elucidate the bonding characteristics and stability of CsCu 2 I 3 . The key findings revealed that Cu-I bonds exhibit high covalency and enhanced resistance to oxidation; Bader charge analysis confirmed the mixed ionic-covalent character in CsCu 2 I 3 . The importance of this study lies in its contribution to the development of low-cost, solution-processable phosphors for solid-state lighting applications. Overall, the CsCu 2 I 3 phosphor was used to fabricate yellow LED with Correlated Color Temperature (CCT) of (4290) K and Commission Internationale de l′Éclairage (CIE) coordinates of (0.38, 0.41).