Comparing the relaxation data for the 1-Ln series, it could be inferred that 1-Nd has the shortest T1 because it has the largest ground state orbital angular momentum (L = 6) and indeed the largest total angular momentum (J = 9/2). However, comparison with T1 data for these Ln 3+ ions at similar concentrations and temperatures in water/ethanol glasses gives a different trend, with Nd 3+ having the longest T1. This emphasises the importance of the crystal field on the relaxation behaviour of Ln 3+ ions. In our case, of the three complexes studied, 1-Nd has, by some margin, the lowest energy excited state and indeed the smallest energy spread of mJ states desite having the largest multiplicity (Tables ). More densely-packed electronic states renders the states more sensitive to perturbations (following textbook perturbation theory arguments), and so we can speculate that this exposes 1-Nd to more influences from spin-vibration coupling, and thus causes a shorter T1.