In the In Your Element 'Terbium glows green' (Nat. Chem. 10, 110; 2018), phosphorescence was mistakenly described as fluorescence in three instances: the standfirst, the fourth paragraph, and the final paragraph. Furthermore, the line from the fourth paragraph “Many of its rare-earth cousins also fluoresce” was changed to “Many of its rare-earth cousins also luminesce”. This has been corrected after print 31 January 2018.