<p>Eu³⁺-doped gadolinium gallium garnet (Gd₃Ga₅O₁₂:<i>x</i>Eu³⁺) phosphors with varying concentrations of Eu³⁺ were prepared by a conventional high-temperature solid-state reaction method. The phase purity and structure of the prepared phosphors were confirmed using x-ray diffraction (XRD) studies. The photoluminescence (PL) and thermoluminescence (TL) properties of Gd₃Ga₅O₁₂:<i>x</i>Eu³⁺ were also investigated. The PL properties of the prepared GGG:Eu³⁺ phosphor exhibited strong emission in the orange–red region at 593–611&#xa0;nm under ultraviolet (UV) excitation. This is because of ⁵D₀→⁷F₁ and ⁵D₀→⁷F₂ Eu³⁺ transitions. In the PL emission spectra of Gd₃Ga₅O₁₂:<i>x</i>Eu³⁺ (<i>x</i> = 0.01–0.08), variation in PL intensity was observed, and the optimal concentration was found at 5&#xa0;mol.%. TL spectroscopy of Gd₃Ga₅O₁₂:<i>x</i>Eu³⁺ (<i>x</i> = 0.01–0.08) was also carried out, and the optimal concentration of Eu³⁺ ions based on the TL glow curve was 2&#xa0;mol.%. Upon varying the UV exposure time for the GGG phosphor doped with 2&#xa0;mol.% Eu³⁺ ions, the maximum intensity was observed for 20&#xa0;min of UV exposure, with a peak centered at 97°C. Color chromaticity and purity were also measured.</p>