ELuminescence and energy transfer of Ce3+/Gd3+/Tb3+/Eu3+ doped hexagonal fluoride

Down-shifting luminescence (DSL) of Rare Earth doped hexagonal fluoride has been utilized for multiple potential applications. However, the DSL energy transfer (ET) mechanism still remains rough sketch. In this work, we synthesized a series of hexagonal fluoride NaREF4 with different components and filled up the details of the ET mechanism by thoroughly investigating the luminescence behaviors and lifetime decay curves of Ce3+/Gd3+/Tb3+/Eu3+. All samples were identified to be pure hexagonal phase by powder X-ray diffraction (PXRD). 5 ET processes including Ce3+-> Gd3+, Ce3+-> Tb3+, Gd3+-> Tb3+, Gd3+-> Eu3+ and Tb3+-> Eu3+ were confirmed and the ET efficiencies could reach up to 69.41%, 61.09%, 88.03%, 83.97% and 70.72%, respectively. According to Dexter's theory, dipole-dipole interaction was found to be responsible. Multiple emission colors could be achieved due to efficient ET Tb3+-> Eu3+. However, Eu3+ couldn't be sensitized by Ce3+, hence it was necessary to distribute them into different layers or introduce Gd3+ as intermediate bridge to realize the sensitization. The detailed ET mechanism supported by the lifetime decay curves were proposed. These fundamental researches could help to design novel RE activated fluorescent materials.