Luminescent and scintillation ceramic materials with complex shapes, which can be created by stereolithography 3D printing, are of interest for special phosphor and detector applications. Starting powders for such ceramics may possess UV absorption bands; therefore, it is important to study the possible influence of the powders’ luminescent properties on the printing process. This paper deals with complex garnet oxides, Y₃Al₅O₁₂ and Gd₃Al₂Ga₃O₁₂—well-known hosts for luminescent materials. The photopolymerization rates of slurries based on the luminescent powders produced by various chemical routes are studied, as well as available printing regimes. The slurries containing Ce-doped powders with a broad absorption band in UV have significantly lower photopolymerization rates compared to the undoped ones; a high Ce doping virtually hinders printing with layers thicker than 25–50 μm. Furthermore, the choice of powder synthesis method is shown to influence the printing process. Slurries with Tb-doped powder, with absorption lines at shorter wavelengths, have good photopolymerization activity, close to that of the undoped powder, and can be printed with layer thicknesses of 25–100 μm.

Dense and transparent ceramic samples of a (Gd,Y)₃Al₂Ga₃O₁₂:Ce scintillator were obtained by using stereolithography-based Digital Light Processing (DLP) 3D printing for compacting, subsequent burnout, and pressureless sintering. The effects of stoichiometric deviations and green body compaction methods (uniaxial pressing versus DLP 3D printing) on the optical, luminescent, and scintillation properties of ceramics were analyzed. An excess of Y and Gd in the composition led to an increase in transmittance and to the acceleration of the scintillation kinetics. Moreover, transparent ceramics made of 3D-printed green bodies were found to be superior in light yield to the samples, which were prepared from the same powders and densified by uniaxial pressing.

The production of scintillating ceramics can require the utilization of the phosphorus compounds at certain stages of 3D-printing, such as vat polymerization, applied for the formation of green bodies before sintering. The effect of phosphorus additive on the microstructure, optical, and scintillation parameters of Gd₁.₄₉₄Y₁.₄₉₄ Ce₀.₀₁₂Al₂Ga₃O₁₂ (GYAGG:Ce) ceramics obtained by pressureless sintering at 1650 °C in an oxygen atmosphere was investigated for the first time. Phosphorus was introduced in the form of NH₄H₂PO₄ into the initial hydroxycarbonate precipitate in a wide concentration range (from 0 to 0.6 wt.%). With increasing of phosphorus concentration, the density and the optical transmittance of garnet ceramics show a decrease, which is caused by an increase in the number of pores and inclusions. The light yield of fast scintillation, which is caused by Ce³⁺ ions, was found to be affected by the phosphorus additive as well. Moreover, an increase in phosphorescence intensity was recognized.

Phosphoric acid ester, a typical component of commercial dispersants, affects the functional properties of Gd_1.494Y_1.494Ce_0.012Al₂Ga₃O₁₂ ceramics. In sintered ceramics, the residual phosphorus can reach up to 40–70% of the introduced amount. The admixture of phosphorus located on the surfaces of the particles activates the grain growth during sintering and leads to the formation of secondary phases of rare-earth phosphates. With increasing phosphorus concentration, the density and optical transmittance of ceramics decrease. A relatively small amount of phosphorus can improve the luminescence properties of ceramics but large amounts can increase phosphorescence and reduce the scintillation light yield.