Dy³⁺-doped CaMg₃(SO₄)₄ (CMS) phosphor was prepared by the acid distillation method and examined in detail with a thermoluminescence (TL) study whereby the phosphor was irradiated with γ-rays and a carbon ion beam. A good dosimetric glow curve was observed that is stable against both types of radiation. The CMS doped with 0.2 mol% of Dy³⁺ showed 3.5 times more sensitivity than commercially available CaSO₄:Dy³⁺ TLD phosphor when irradiated with a carbon ion beam. The observed glow curve variation and resultant variation in the values of trapping parameters with a change in ion beam energy suggest more complex interactions of ion beam within the phosphor at higher energies.