Copper(I) iodide (CuI)-based inorganic-organic hybrid materials in the general chemical formula of CuI(L) are well-known for their structural diversity and strong photoluminescence and are therefore considered promising candidates for a number of optical applications. In this work, we demonstrate a systematic, bottom-up precursor approach to developing a series of CuI(L) network structures built on CuI rhomboid dimers. These compounds combine strong luminescence due to the CuI inorganic modules and significantly enhanced thermal stability as a result of connecting individual building units into robust, extended networks. Examination of their optical properties reveals that these materials not only exhibit exceptionally high photoluminescence performance (with internal quantum yield up to 95%) but also that their emission energy and color are systematically tunable through modification of the organic component. Results from density functional theory calculations provide convincing correlations between these materials' crystal structures and chemical compositions and their optophysical properties. The advantages of cost-effective, solution-processable, easily scalable and fully controllable synthesis as well as high quantum efficiency with improved thermal stability, make this phosphor family a promising candidate for alternative, RE-free phosphors in general lighting and illumination. This solution-based precursor approach creates a new blueprint for the rational design and controlled synthesis of inorganic-organic hybrid materials.