These positions are placed within the crystals and they provides a short lifetime close to several microseconds which corresponds to direct Volasertib transfer between Eu ions. The positions with perturbed local symmetry provide so called “extrinsic” emission. The extrinsic emission is characterized by a long radiative lifetime. The prolongation of the lifetime reflects the change of the energy transfer mechanism. It is usually by back-transfer of energy from extrinsic to intrinsic ions . In case of nanocrystalline materials the perturbations are located mainly on the surface of the nanoparticles.