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Lithium doping has been widely employed to modulate the photoluminescence of lanthanide-doped crystals. Despite its effectiveness, the underlying mechanism remains debatable. Using cubic sodium yttrium fluoride as a model crystal, first-principles calculations indicate that neutral substitution of host sodium with lithium ions can occur, irrespective of synthesis conditions. Unlike lithium substitution, the formation of lithium interstitials is likely accompanied by the substitution of F- with O2- ions. The lithium substitution shows negligible influence on the electronic structures of the host crystal and the 4f orbital energies of lanthanide ions. By comparison, the lithium-oxygen defect pairs could induce self-absorption losses in lanthanide luminescence or produce ligand-to-metal charge transfer states that could populate lanthanide 4f states.

The beltline region of the reactor pressure vessel (RPV) is subject to an extreme radiation, temperature, and pressure environment over several decades of operation; therefore it is necessary to understand the mechanisms through which radiation damage occurs and how it affects the mechanical and chemical properties of the RPV steel. Chemical rate theory is a mean field rate theory simulation model which applies chemistry to the evaluation of irradiation-induced embrittlement. It presents one method of analysis that may be coupled to other distinct methods, in order to analyze defect formation, ultimately providing useful information on strength, ductility, toughness and dimensional stability changes for effects such as embrittlement, reduction in ductility and toughness, void swelling, hardening, irradiation creep, stress corrosion cracking, etc. over time as materials are subjected to reactor operational irradiation. This paper serves as a brief review of rate theory fundamentals and presents several examples of research that exemplify the application and importance of rate theory in examining the effects of radiation damage on RPV steel.