Glass-based phosphors have applications that range from light-emitting diodes to lasers. The optical properties of these materials depend on the coordination environment of the dopant luminescence centres, which is expected to change significantly as the dopant concentration is increased. However, it is difficult to probe this coordination environment over the short and intermediate length scales that govern the luminescence efficiency. Here, we will use high-resolution neutron diffraction to make a systematic investigation of this issue for Mn doped zinc phosphate glass. In particular, the evolution in glass structure will be followed as Zn is replaced completely by Mn. The results will be combined with those obtained from other methods in order to link the composition dependent change in the luminescence to the change in coordination environment of Mn on multiple length scales.