Disclosed herein are phosphor compositions having high gadolinium concentrations. Some embodiments include a thermally stable ceramic body comprising an emissive layer, wherein said emissive layer comprises a compound represented by the formula (A1-x-zGdxDz)3B5O12, wherein: D is a first dopant selected from the group consisting of Nd, Er, Eu, Mn, Cr, Yb, Sm, Tb, Ce, Pr, Dy, Ho, Lu and combinations thereof; A is selected from the group consisting of Y, Lu, Ca, La, Tb, and combinations thereof; B is selected from the group consisting of Al, Mg, Si, Ga, In, and combinations thereof; x is in the range of about 0.20 to about 0.80; and z is in the range of about 0.001 to about 0.10. Also disclosed are thermally stable ceramic bodies that can include the composition of formula I. Methods of making the ceramic body and a lighting device including the ceramic body are also disclosed.