And what the second point of Aufbau says is that as electrons begin to fill those levels the differences in energy may shift so that in an unoccupied state certain levels may be in the inverse order from how they are in the occupied state.

构造原理谈到的第二点是,当电子开始布满这些层时,能量差可能会有改变,所以在一个未占据的确定能级,可能与它们占据时,的排布顺序是相反的。

麻省理工公开课 - 固态化学导论课程节选

And this is an example where unoccupied 5d lies below 4f.

这就说明,未布满的5d层在4f层下面。

麻省理工公开课 - 固态化学导论课程节选