Improving the blue emission from Eu²⁺ by codoping Re³⁺ ions (Re--Y, La, Gd, Lu) in NaMgPO₄

Codoping Ce3+ is an effective strategy to improve the blue emission from Eu2+ in NaMgPO4:Eu2+ phosphor, while the origin of the luminescence enhancement is still ambiguous. Here, Re3+ (Re--Y, La, Gd, Lu) ions instead of Ce3+ are codoped into NaMgPO4:Eu2+ phosphor and the effect of Re3+ substituting for Na+ on the photo-luminescence and photo-phosphorescence properties is investigated. Codoping Re3+ enhances the emission in-tensity of Eu2+ greatly, as observed by measuring the optical properties. We suggest that codoped Re3+ ions could stabilize Na + vacancies via a charge compensation process, prompt the reduction of Eu3+ to Eu2+, increase the number of Eu2+ ions, and finally improve the luminescence properties. Meanwhile, a blue-or red-shift behavior of Eu2+ emission is witnessed in NaMgPO4:Eu2+,Re3+ system, depending on the size of Re3+ ions. This could be attributed to the alterable crystal field splitting for Eu2+ caused by the incorporation of Re3+ ions. All the results suggest that codoping Re3+ has an obvious influence on the luminescent behavior of Eu2+ in this system. This work also promotes research on the effect of codoping Ce3+ on the luminescence properties of NaMgPO4:Eu2+ phosphor, and offers new ideas for developing Eu2+-activated phosphors.