Diamagnetic Lanthanoid ions are:
$\text{La}^{3+} { \& } \text{Ce}^{4+}$
$\text{Nd}^{3+} { \& } \text{Eu}^{3+}$
$\text{Lu}^{3+} { \& } \text{Eu}^{3+}$
$\text{Nd}^{3+} { \& } \text{Ce}^{4+}$