Photocathodes working in reflection-mode are made of rich-diamond (R-D) and rich-graphite (R-G) nanodiamond (ND) layers, deposited on different conductive substrates by means of the pulsed spray technique at low deposition temperatures (120 and 150 °C) and starting from two types of ND particles. The two powders with an average grain size of 250 nm have variable sp2 (graphite phase) and sp3 (diamond phase) hybridized carbon contents, as assessed by Raman spectroscopy and transmission electron microscopy. The ND particles are employed as-received or treated in H2 microwave plasmas.The principal aim of the paper is the comparative study of R-D and R-G photocathodes in the vacuum ultraviolet spectral range from 140 to 210 nm, where they exhibit a high quantum efficiency and a good stability over time upon exposure to air. Specifically, the quantum efficiency values at 140 nm of …