La2O3	—0.001–0.01% each Al, Ca, and Si; 0.0001–0.001% each Ag, Cu, and Mg; questionable Pr.
Nd2O3	—0.01–0.1% Eu; 0.001–0.01% each Ho, La, Si, and Yb; 0.0001–0.001% each Ca, Cu, Fe, Lu, Mg, Tm, and Y; <0.0001% each Ag and Mn; questionable Al, Cr, Er, and Ni.
Sm2O3	—0.01–0.1% Dy; 0.001–0.01% each Gd, La, Si, and Tm; 0.0001–0.001% each Eu, Fe, Ho, Mg, Y, and Yb; <0.0001% each Ca, Cu, and Mn; questionable Ag, Al, and Ni.
Gd2Os	—0.03% Tb; 0.05% Eu; 0.001–0.01% each Cu and Si; <0.0001% Al.
Dy2O3	—0.006% Y; 0.13% Ho; 0.01% Er and Tm; and 0.001–0.01% each Cu and Si.
HO2O3	—0.07% Er; 0.001–0.01% Si.
Er2O3	—0.001–0.01% each Mn and Si.
Tm2O3	—0.01–0.1% each Er and Lu; 0.001–0.01% each Dy, Ho, La, Si, Y, and Yb; 0.0001–0.001% each Ca, Cu, Fe, and Mg; <0.0001% Ag; and questionable Eu, Gd, and Mn.
Yb2O3	—0.001–0.01% each Er, Lu, Si, and Tm; 0.0001–0.001% each Cu, Fe, Mg, and Y; <0.0001% each Ca and Mn; and questionable Ag and Ce.
Lu2O3	—0.01–0.1% Er; 0.001–0.01% each Dy, Si, Y, and Yb; 0.0001–0.001% each Cu, Mg, and Tm; <0.0001% Ca; and questionable Ag, Eu, and Mn.