Solvated electrons are highly reductive chemical species involved in many reactions from radiochemistry to photocatalysis. Different sources have been considered for the emission of solvated electrons from ionic precursors, 2 metals, metal oxides or diamond surfaces. Diamond materials are particularly interesting due to the negative electron affinity (EA) of the diamond surface when terminated e.g. with hydrogen atoms, enabling a spontaneous and barrier-free electron emission once electrons are excited into the conduction band. Especially, diamond has been used to trigger chemical reduction of nitrogen or carbon dioxide directly in the aqueous phase using electrochemical reaction or light excitation. The latter represents a great challenge due to the large bandgap of diamond of 5.5 eV, necessitating the use of deep ultraviolet (DUV) light, which is absent from the solar spectrum. So far, clear evidence of the light-induced emission of solvated electrons from diamond in water is scarce. It was recently shown for hydrogenated nanodiamonds (NDs) in aqueous suspensions under X-ray irradiation. Indirect demonstration were provided on boron doped diamond electrodes, NDs 14 and silver-doped diamond thin films. In a seminal work, Zhu et al. demonstrated that upon DUV light excitation, a transient signal at 633 nm was observed in water above a diamond single crystal which was assigned to solvated electrons. It was recently completed by a detailed study of transient absorption in the ns-µs range, showing sub-bandgap electron emission for excitation down to 4.5 eV (275 nm). Nevertheless, the time evolution over the early stages (< 2 ns) of the electron emission under DUV light remains unexplored to our knowledge. Achieving electron emission with visible (VIS) light excitation instead of DUV light would also be required for a larger significance of diamond in the field of photocatalysis. A promising strategy to achieve solvated electron emission with VIS light consists in adding new electronic states within the bandgap of the diamond material than can then be excited with VIS photons above the diamond conduction band maximum (CBM). Several strategies were employed to achieve sub-bandgap absorption, including dye sensitization, plasmonic coupling, nanostructuring 17 and doping. The main challenge is, however, to retain the electron emission properties offered by Hterminated surfaces. Sub-bandgap visible absorption with diamond materials was previously reported in vacuum but remains to be shown in water. Visible-light reactivity toward CO2 photoelectrochemical reduction was recently demonstrated on hydrogenated nanostructured diamond surface by some of us. The origin of enhanced reactivity with visible light remains elusive so far. Thus, identifying electron emission processes involved in sub-bandgap (visible) excitation would certainly facilitate the design of more efficient diamond-based electron emitters. In this study, we have employed ultrafast transient absorption (TA) spectroscopy with sub-ps time resolution to monitor the early stages of solvated electron emission from detonation NDs in water. Aqueous dispersions of NDs with hydrogenated (ND-H), carboxylated (ND-COOH) and hydroxylated (ND-OH) surface were compared. The impact of excitation photon energy was studied by applying both DUV (225 nm, 5.5 eV) and VIS (400 nm, 3.1 eV) pump laser pulses. All ND surface terminations were found to enable the emission of solvated electrons with DUV light. Furthermore, a substantial solvated electron emission was observed for ND-H under visible light. Based on these TA measurements and density functional theory (DFT) calculations, possible mechanisms for the emission of solvated electrons in DUV and VIS regions are proposed.