General order and mixed order fits of thermoluminescence glow curves—a comparison

Abstract

General order (GO) and mixed order (MO) kinetics expressions are applied to a series of synthetic thermoluminescence (TL) glow peaks derived from different physical models. The correlation between kinetic order (KO) parameter b of the GO kinetics expression and the parameter α (=n 0/(n 0+M) where n 0 is the initial filled concentration of the active traps and M that of the thermally disconnected deep traps) of the MO expression is checked. It is found that the correlation is not universal except at the limiting values of α and b, when α=0 and 1 always correspond to b=1 and 2 as expected. In the intermediate region the graphical plot does not produce a smooth line. An examination of all the results along with those from the published literature shows that the overall scatter in the values found for b corresponding to any value found of α is within about ±10%. This scatter is attributed to the influence of parameters other than α and b on the symmetry of the glow peak. A conclusion of greater significance reached from this study is that MO expression is a superior alternative to GO for the glow peak characterization. This is because the parameter α remains constant at all temperatures T in the glow curve whereas b, though assumed constant in the GO expression, changes with T when GO is applied to any physically plausible model of TL emission, except when b turns out to be 1 or 2. Due to this variation of b, the value found for E always has some error which increases systematically as the fitted b deviates farther away from 1 and 2. Parallel to the error in E, the figure of merit (FOM) of the fit also deteriorates. The paper also discusses the relevance of other fitted parameters, both in GO and MO fits.