Defect driven tunable optical properties of Li+ and Zr4+ co-doped Eu3+: MgF2 compounds

Highlights: • PL properties of Eu³⁺: MgF₂ phosphor were tuned by using Li⁺ and Zr⁴⁺ as co-dopant ions. • Various Mg-vacancies and their cluster forms are responsible for the tunable emission characteristics. • Fist principal study helped to understand the configuration of various cluster vacancies. -- Abstract: A novel approach of defect engineering in Eu³⁺ doped MgF₂ compounds has been carried out in order to tune the optical properties of Eu³⁺ ion. Upon doping various co-dopant ions such as Li⁺ and Zr⁴⁺ ions, it has been observed for the first time in the photoluminescence (PL) study that such co-dopant ion would control the characteristics transition lines of Eu³⁺ ions and results in tunable color characteristics of the phosphor materials. While Li⁺ co-doping results in a higher intense magnetic dipole (MD) line (⁵D₀ → ⁷F₁), doping with Zr⁴⁺ results in an intense electric dipole (ED) line (⁵D₀ → ⁷F₂). Further, Li⁺ co-doping also results in an unusual highly intense ⁵D₀ → ⁷F₄ line. From PL decay profile it has been observed that although for both cases of the co-dopant ions two different Eu³⁺ components are found to exist, their contribution is completely different. From positron annihilation lifetime study it was observed that various Mg-vacancies and their cluster forms are responsible for the tunable emission characteristics. First principle based theoretical study has also been carried out to understand the configuration of various cluster vacancies as suggested by their respective positron lifetime values. The short-lived Eu³⁺ component, which gives rise to highly intense ⁵D₀ → ⁷F₄ line, originates from a Mg-site at the surface of the particle and close to a vacancy cluster VC1. While the long lived Eu³⁺ component is responsible for highly intense ED line and close to Mg mono- or di-vacancies in the bulk of the particle. Therefore, defects (both dopant impurity ions and lattice vacancies) play a significant role in tuning the emission characteristics of Eu³⁺ doped MgF₂ compounds.