Seminarium (dr hab. Vitaliy Vistovskyy)
Dnia 19.02.2019 odbędzie się seminarium, którego referentem będzie dr hab. Vitaliy Vistovskyy: Relaxation and migration of electronic excitations in scintillation materials in case of space confinement.
Studies of self-trapped exciton an impurity luminescence upon optical and X-ray excitation were performed for different type of nanoparticles of various sizes in the range of 8-100 nm. It was shown that in the case of high energy excitation besides the non-radiative decay of luminescence centers due to interaction with surface defects, in nanoparticles the excitation energy losses during migration of free charge carriers are important. The hypothesis that the main energy losses in small nanoparticles in the case of X-ray excitation and excitation in the range of low-energy band-to-band absorption occur during thermalization of charge carriers due to reach the surface, where they can relax interacting with surface defects or leave the nanoparticles is proposed.
Size effect for core-valence luminescence parameters was studied on BaF2 nanoparticles. It was revealed that the intensity of core-valence luminescence of BaF2 nanoparticles upon the excitation with synchrotron radiation is much less dependent on the nanoparticle size compared to the intensity of impurity or self-trapped exciton luminescence.
The proposed mechanism of X-ray excited exciton and impurity luminescence quenching indicates the direction for search of nanomaterials that can possess an intense X-ray excited luminescence. Such materials should reveal as small as possible thermalization length of free charge carriers.