Abstract Metal-doped benzil crystals have been grown by thermal gradient solidification in a vertical transparent growth configuration to investigate the effect of metallic guest on the ordered organic host. We have identified the conditions for growing homogeneous, optically good crystals of benzil doped with sodium and silver, limiting the effect of supercooling, low thermal conductivity and anisotropy of the growth speed (temperature gradient at the liquid–solid interface: 10–25 °C, moving speed of the growth interface 2.0 mm/h). The nature and concentration of the dopant are parameters affecting, through the growth process, the crystalline perfection and the optical properties of the organic matrix. Bulk optical characterisation, by spectrophotometrical methods, has offered details on some intrinsic properties of the system metal particles/benzil crystalline matrix. Analytical processing of the experimental data emphasised that benzil is a wide optical band gap organic semiconductor E g = 2.65 eV . We also have investigated the effect of sodium and silver on the properties of benzil crystal as potential transparent semiconductor matrix for (nano)composite metal/molecular organic material. With the increase of sodium concentration from c = 1 to 6 wt%, a small narrowing of the band gap has been remarked. The same behaviour has been found for benzil doped with silver ( c = 2 wt % ) compared to pure benzil.