Ammoniate Intermediates Enable Tunable Biphasic Molten Salt/Organic Synthesis of Colloidal GaN Nanocrystals

We report a systematic investigation into the biphasic synthesis of gallium nitride (GaN) nanocrystals using molten gallium halide salts and organic amines, with a particular focus on the role of ammoniate intermediates as viable precursors for GaN quantum dot synthesis. By systematically varying the identity of organic amine and the ammonia-to-gallium ratio in GaN biphasic reactions, we elucidate key parameters governing GaN formation, phase selectivity, and size control. Ammonia was shown to be convenient for nitride formation, with GaI3 readily forming gallium ammoniate intermediates upon exposure. These intermediates, particularly in their lower-ammoniate forms (e.g., GaI3·1NH3), enabled GaN nucleation upon heating, while higher-order ammoniates (e.g., GaI3·7NH3) were unable to nucleate new crystalline GaN but participated in the growth of GaN nanocrystals. By adjusting the ratio of nucleation-initiating to growth-directing ammoniate precursors, nanocrystal diameters could be tuned from 2 to 12 nm. Additionally, halides present during the synthesis provide control over nanocrystal phase (i.e., zinc blende vs wurtzite). These results provide new insights into the complex reactivity landscape of GaN colloidal synthesis and establish ammoniate intermediates as key precursors for producing tunable III–N nanocrystals.