it is more interesting to note that the same material of larger particle size is more sensitive to TL response as compared to its nano-form., It may be due to a decrease in the volume to surface ratio in the case of nanomaterials leading to a decrease in the number of defects formed (within the volume of the crystals) , that we find a decrease in TL sensitivity on decreasing the particle size.

There is a fundamental difference between thermoluminescence of micro- and nanocrystalline forms of the same material that the traps and luminescence centers are different. This is because the energy levels get reorganized as we go from micro to nano. It is well known that the band gap of the host increases as the size reduces and thus that of the local levels of the impurity(ies). Moreover, the crystal field effect plays important role in the glow curve structure and the it changes with the shape and size of the crystallites. Another important change is in their dose responses that the later (nanomaterials) have very wide dose ranges and are very useful for estimating very very high doses of the order of several hundreds of kGy. They are more sensitive to any little change inside these crystallites, such as, morphology, phase change, redox reactions of the doped impurities, changes due to clustering of such impurities and so on. There are several of our publications which show that nanocrystalline materials are important for better understanding of the phenomenon of luminescence in general and thermoluminescence in particular. 

Beside the perfect answer of Professor P. D. Sahare, you can search about the Track Interaction Model (TIM) which can distinguish between the interaction of radiation with a microcrystalline material and nanocrystalline material.