Abstract The luminescence spectra of a diversity of chromium doped borate glasses were analysed. In these glasses the dopant ions are subject to a high average crystal field. For a particular set of ions the field is high enough to cause the lowest excited state to be the 2 E level and high quantum efficiencies could be expected. However, there is a strong destructive influence of the nearby 4 T 2 level. In a ZnO containing glass microcrystallites were optically identified as ZnCr 2 O 4 spinels. In the formation of these crystallites Al 2 O 3 plays an important role.