Rare earths include the fifteen lanthanide metals along with yttrium and scandium.

VOA: special.2010.10.08

As soon as lanthanum takes that electron, this level rises ever so slightly, and then we jump down here and fill in the lanthanide.

一旦镧得到了电子，这一层就会稍稍上升，然后我们向下填一下镧系元素。

麻省理工公开课 - 固态化学导论课程节选