Red or Green: Understanding the Formation Mechanism of (Mg,Zn)xGeOy Persistent Luminescent Phosphors and the Mn2+ Occupancy in Them

Two germanate compounds, MgGeO 3 and Zn 2 GeO 4 , have been employed as host lattices for persistent luminescent (PersL) phosphors. When doped with the same activator, Mn 2+ , MgGeO 3 produces red PersL, while Zn 2 GeO 4 exhibits green PersL. In this work, we combine these two hosts to form a quaternary oxide (Mg,Zn) x GeO y , enabling dual red-green PersL from a single dopant Mn 2+ . Due to the different reactivity and formation energies of MgGeO 3 and Zn 2 GeO 4 , we found that the red-to-green emission is highly sensitive to the synthesis pathway, even when identical precursor stoichiometries were used. To uncover the origin of this behaviour, we compared three solution-based synthesis routes for Mn 2+ -doped (Mg,Zn) x GeO y , and systematically analyzed their phase compositions, Mn 2+ site occupancy, and trap characteristics. Remarkably, only the ultrasound-assisted synthesis promoted the formation of a uniform quintenary compound, in which Zn and Mg simultaneously substitute for each other in the MgGeO 3 and Zn 2 GeO 4 hosts, respectively, resulting in PersL that can be activated by low-energy, deep purple light instead of ultraviolet light. Subsequent thermoluminescence measurements revealed a distinct trap state responsible for the dual-color PersL. These findings demonstrate a synthetic strategy to tune multi-color PersL through controlled cation substitution and highlight the crucial role of synthesis conditions in engineering novel PersL materials.