Using DFT Methods to Study Activators in Optical Materials

Density functional theory (DFT) calculations of various activators (ranging from transition metal ions, rare-earth ions, ns² ions, to self-trapped and dopant-bound excitons) in phosphors and scintillators are reviewed. As a single-particle ground-state theory, DFT calculations cannot reproduce the experimentally observed optical spectra, which involve transitions between multi-electronic states. However, DFT calculations can generally provide sufficiently accurate structural relaxation and distinguish different hybridization strengths between an activator and its ligands in different host compounds. This is important because the activator-ligand interaction often governs the trends in luminescence properties in phosphors and scintillators, and can be used to search for new materials. DFT calculations of the electronic structure of the host compound and the positions of the activator levels relative to the host band edges in scintillators are also important for finding optimal host-activator combinations for high light yields and fast scintillation response. Mn⁴⁺ activated red phosphors, scintillators activated by Ce³⁺, Eu²⁺, Tl⁺, and excitons are shown as examples of using DFT calculations in phosphor and scintillator research.