Nd³⁺-doped Y₃Al₂Ga₃O₁₂ garnet ceramic pellet was prepared by solid state reaction and used as prototype to investigate the potential of Nd³⁺-activated garnet phosphors as Boltzmann thermometers for cryogenic and high temperature ranges. Despite the conventional use of the near-infrared emitting Nd³⁺-activated phosphors for biological applications, their real use is hindered by a low sensitivity in the physiological temperature range. Instead, the photoluminescence analysis in the 100–800 K range demonstrated interesting performances in both the cryogenic and high temperature ranges. Indeed, by taking advantage of the Stark levels of ⁴F_3/2 (Z-levels) and the ratio between the emission from the ⁴F_5/2 and the ⁴F_3/2 excited states is possible to build two reliable Boltzmann thermometers in the same material working in the cryogenic temperature range (100–220 K) and at high temperatures (300–800 K), respectively.