Thermal degradation of blue phosphor BAM:Eu2+ under air is investigated using XPS, XRD, EPR and photoluminescence (PL) in order to analyze the loss of intensity in terms of modifications of the dopant distribution in the crystal cell and between crystal bulk and surface. This study reveals the key role played by oxidation-driven 2D diffusion of europium and barium, that results in important concentration gradients and makes degradation strongly dependent on both microstructure and cooling speed. Also based upon cation mobility, a possible regeneration effect is evidenced at moderate temperature. Flux treatments, known to increase the intensity of photoluminescence, also appear to reduce thermal degradation by lowering specific surface: they also enhance the regeneration process by forming extended single-crystal domains conducive to cation diffusion. (C) 2013 Elsevier B.V. All fights reserved.