Scintillation activated by nanoparticle formation in CsI:Na thin films

The scintillation mechanism in Na-doped CsI (CsI:Na) crystalline thin films grown by vacuum deposition has been investigated from the aspects of optical and structural properties. It is found that a heat treatment of the thin film activates the Na-related luminescence corresponding to the dominant scintillation in a CsI:Na crystal. The surface morphology of the thin films measured by atomic force microscope demonstrates that the heat treatment causes the formation of nanoparticles. From the excitation spectrum of the Na-related luminescence and the temperature dependence of the luminescence properties, it is concluded that the scintillation of CsI:Na is caused by the energy transfer from the host material of CsI to NaI nanoparticles.