Characteristic dimensions and evolution times of regions of secondary electronic excitations created by the interaction of ionizing radiation with matter cannot be measured directly. At the same time these are essential parameters both for engineering of nanostructured composite materials defining optimal layer thickness and nanoparticles radii and for the development of optimized scintillators. The paper demonstrates how such spatial and temporal data can be extracted from luminescence decay kinetics excited by vacuum ultraviolet (VUV) and X-ray photons at modern sources of synchrotron radiation MAX IV and PETRA III. Specific features of energy-band structure of self-activated crystal CeF3 are discussed, and its potential for a super-fast detection of ionizing radiation evaluated. Diffusion-controlled dipole–dipole interaction of Frenkel excitons is demonstrated to account well for the luminescence non-exponential decay kinetics providing information on the scales of excited regions created by photons of different energy. For 20 eV photons the radius of excited regions is estimated to be 10 nm, and for 200 eV photons it increases to 18 nm. Effective radius of excited regions of complicated shape created by 19 keV is as large as 80 nm and the diffusion length of Frenkel excitons over radiative time is 14 nm.

The emission spectrum of electron intraband luminescence was calculated for a dielectric crystal with conduction band consists of multiple parabolic branches. This shape of this spectrum adequately correspond to the CsI experimental spectra in the photon energy region ≥ 1.2 eV. The calculated total quantum yield of intraband luminescence of CsI is about 78 photons collected by the silicon photomultiplier per 1 MeV of deposited energy of ionizing radiation. This value is about two times higher than the experimental one, the difference is due to the simplification of the model. It was shown that characteristic times of intraband luminescence are about 1 ps.

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