Nonmonotonic dose dependence of OSL intensity due to competition during irradiation and readout

The nonmonotonic dose dependence of thermoluminescence has been observed in several materials; a recent publication (Lawless, J.L., Chen, R., Lo, D., Pagonis, V., 2005. A model for non-monotonic dose dependence of thermoluminescence (TL). J. Phys. Condens. Matter 17, 737–753.) gave a theoretical account based on competition between trapping states or recombination centers during the excitation and/or readout stages. A similar effect has been observed in the optically stimulated luminescence (OSL) of some materials such as quartz and Al2O3:C (e.g., Yukihara, E.G., Whitley, V.H., McKeever, S.W.S., Akselrod, A.E., Akselrod, M.S., 2004a. Effect of high-dose irradiation on the optically stimulated luminescence of Al2O3:C. Radiat. Meas. 38, 317–330; Yukihara, E.G., Gaza, R., McKeever, S.W.S., Soares, C.G., 2004b. Optically stimulated luminescence and thermoluminescence efficiencies for high-energy heavy charged particle irradiation in Al2O3:C. Radiat. Meas. 38, 59–70.). The model of competition has now been developed to explain the nonmonotonic dose dependence of OSL. A distinction is made between two cases. In one, the competition during excitation causes the filling of the relevant radiative center to be nonmonotonic with the dose, and as a result, the OSL intensity behaves in a similar way. This can take place with a “minimal” model including one trapping state and two kinds of recombination centers, one radiative and the other nonradiative. In the other case, all the relevant concentrations increase monotonically with the dose, and the nonmonotonic dose dependence of the OSL signal is mainly due to competition in the readout stage. In this case, it appears that the requirement for nonmonotonic dose dependence is a system with two trapping states and two kinds of recombination centers.