Diffuse reflectance spectra at room temperature have been collected on polycrystalline perovskite (CaTiO3), zirconolite (CaZrTi2O7) and thorutite (ThTi2O6) samples doped with Np. The Np species give rise to a number of broad, unresolved intraconfigurational f-f electronic transition bands in the near-infrared and visible spectral regions. Both Np3+ and Np4+ can substitute in the Ca site of perovskite by the appropriate choice of charge compensation and sintering atmosphere. No detectable spectral differences were observed when Np4+ was targeted towards either the Ca or Zr sites in zirconolite. Np4+ but not Np5+ can be incorporated in the Th site of thorutite by sintering in air. Even in the most dilute [≤ 0.03 formula units (f.u.)] Np4+ samples of the different titanates studied, there was only very approximate agreement with the Kubelka-Munk law. Crown Copyright © 2007.