Submicron Al2O3 powders with the surface activated by dielectric barrier discharge exhibit an improved performance in wet deposition of ceramic layers. In addressing the possible mechanisms responsible for observed improvement, a comprehensive thermoluminescence (TL) study of plasma activated powders was performed. The TL offers a unique possibility of exploring the population of intrinsic electrons/holes in the charge trapping states. The study covers a wide range of experimental conditions affecting the TL of powders: treatment time, plasma working gas composition, change of discharge configuration, step-annealing of powder, exposure to laser irradiation, aging time. Deconvoluted TL spectra were followed for the changes in their relative contributions. The TL spectra of all tested gases (air, Ar, N2 and 5% He in N2) consist of the well-known main dosimetric peak at 450 K, and the similar magnitude peak at higher temperatures, centered between 700 - 800 K depending on the used working gas. N2 plasma treatment gave rise to a new specific TL peak at 510 K, which exhibited several peculiarities. Initial thermal anealing of Al2O3 powders led to its significant amplification (unlike in other peaks); the peak was insensitive to optical bleaching; and it exhibioted a slow gradual growth during the long-term aging test. Besides its relevance to the ceramic processing studies, presented comprehensive set of data provide a useful and unconventional view on plasma mediated material changes.