© 2022 Elsevier B.V.Carbon dots (CDs), versatile nanomaterials with unique photophysical and structural properties, often have excitation-dependent fluorescence due to the presence of carboxylic groups on the surface of the nanostructure. The excitation-dependent fluorescence of CDs is valuable for bioimaging, but considered undesirable for applications where monochromatic emission is required. Here in this paper, we demonstrate a green, fast and simple way to control the excitation-dependent fluorescence of CDs by passivating carboxylic groups on the surface of CDs with zinc (II) ions through a microwave synthesis method. Conventional CDs without surface passivation had excitation-dependent fluorescence, whereas zinc(II) ion-passivated CDs had excitation-independent fluorescence. Also, the surface passivation of CDs led to an increase in the quantum yield of CDs. The present work provides an inexpensive and user-friendly way to develop carbon dots with controllable emission properties by incorporating a metal ion into carbon dots through simple microwave-assisted synthesis.