High-sensitivity radioluminescence (RL) and thermoluminescence (TL) measurements were carried out on samples of natural leucite (with 2.95% of Na₂O) from Campania Vessa (Italy). Samples were annealed to modify the charge compensation through alkali metal self-diffusion and to produce luminescence centres. High-temperature powder diffraction, scanning electron microscopy and chemical analyses were performed to monitor the tetragonal–cubic phase transitions and the thermal drainage of alkali metal ions from the aluminosilicate lattice. The emission spectral bands of leucite (300, 380, 430, 480, 560 and 680 nm) match those of other Na/K-aluminosilicates (alkali metal feldspars) and could be attributed to similar defects. TL glow curves of increasingly pre-irradiated natural leucite (range 0–20 Gy) showed no changes above 300 °C, whereas some changes were observed with annealed samples (1000 °C for 12 h). This temperature is the starting point of Na self-diffusion within the aluminosilicate lattices. The areas of the TL glow curves of both natural and annealed β-irradiated leucites can be fitted with a linear function with high correlation. These results are in agreement with high alkali metal loss (K₂O ∼12% and Na₂O ∼18%) during thermal pre-treatment, high cell volume expansion (from 2350 to 2500 Å) and the cubic Ia3d ⇌ tetragonal I4₁/a phase transition. This promotes the egress of alkali metal ions and the production of [AlO₄/M⁺]°, [AlO₄/H⁺]° and [AlO₄]° luminescence centres.