Parametric study of plasma-mediated thermoluminescence produced by Al₂O₃ sub-micron powders

Sub-micron Al₂O₃ powders with a surface activated by dielectric barrier discharge exhibit improved performance in wet deposition of ceramic layers. In addressing the possible mechanisms responsible for the observed improvement, a comprehensive thermoluminescence (TL) study of plasma-activated powders was performed. TL offers the unique possibility of exploring the population of intrinsic electrons/holes in the charge trapping states. This 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 and 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 a peak of similar magnitude at higher temperatures, centered between 700 and 800 K depending on the working gas used. N₂ plasma treatment gave rise to a new specific TL peak at 510 K, which exhibited several peculiarities. Initial thermal annealing of Al₂O₃ powders led to its significant amplification (unlike the other peaks); the peak was insensitive to optical bleaching, and it exhibited slow gradual growth during the long-term aging test. Besides its relevance to the ceramic processing studies, a comprehensive set of data is presented that provides a useful and unconventional view on plasma-mediated material changes. (paper)