Rare-earth-doped, polycrystalline yttria-gadolinia ceramic scintillators with high density, optical clarity, uniformity, cubic structure and which are useful in the detection of x-rays, include one or more of the oxides of rare earth elements Eu, Nd, Yb, Dy, Tb, and Pr as activators. The ceramic scintillator may also include CaO, SrO, and Yb.sub.2 O.sub.3 as afterglow reducers. Sintering, sintering combined with gas hot isostatic pressing, and hot pressing methods for preparing the ceramic scintillators are also described.