An optical investigation of nano-crystalline CaF2 particles doped with Nd3+ ions

•Optical spectroscopic studies of nanoparticles CaF2 doped with Nd3+ ions clearly identified core and surface related luminescence defect centers.•The origin of the surface or near surface defect, A′, centre has been ascertained to be derived from a single-ion centre most probably charge compensated by a hydroxyl group.•It highlight the power and usefulness of the spectroscopic technique of zero-order excitation in the characterisation of the luminescence of sub-micron particles.