Organic–inorganic hybrid metal halides are well known for their structural flexibility and high photoluminescence quantum yield (PLQY), showing great potential for optical applications. In this work, we demonstrate the synthesis of a series of alkali copper(I) iodide (ACuI)-based (A = Na, K, Rb, and Cs) organic–inorganic hybrid materials with different structures and emission peaks by adjustment of the alkali atoms and organic molecules. These compounds possess strong PL with emission peaks in the range of 530–660 nm, the highest PLQY of 91% was achieved for KCuI₂(C₄H₈OS)₂, and their different emissions originate from distinct charge-transfer processes. Green, yellow, and red light-emitting diodes (LEDs) can be fabricated by using these materials, and a white LED based on all-copper iodide phosphors is demonstrated with a high color rendering index of 93 by utilizing a mixture of blue-emissive Cs₃Cu₂I₅ and yellow-emissive Rb₂Cu₂I₄(C₄H₈OS)₃ powders. This work provides a new strategy for the development of hybrid copper halides with composition-tunable structures and high performance and demonstrates that this series of (ACuI)-based compounds could be candidates for emission applications, including lighting or display.