LAUSR

REPO4 (RE = La, Gd, Lu, Y) serves as an excellent host lattice due to its stable physicochemical properties and optical inertia. Doping Gd3+(La3+) into LuPO4 can form mixed crystals, increasing the Gd3+(La3+) concentration will induce the phase transition from tetragonal to hexagonal lattices, and the variation of the local structure around the Ce3+ activator will influence its 5d-level position and consequently 5d → 4f radiation transition. This can be attributed to the synergy effect of rare earth ions in REPO4, however, the essential mechanism of such a synergy effect on the local structure and optical property is still poorly understood. Here, we study the synergy effect of rare earth ions on the phase transition and PL emission in a Ce3+:REPO4 system on the basis of the relationship between the composition-dependent local structure around Ce3+ and its PL emission properties from a molecular view. The competition between Lu3+ and Gd3+(La3+) in REPO4 not only influences the relative atomic position but also varies the symmetry of anion groups. Infrared absorption bands indicate that the activation of P-O bonding promotes phase transition and enhances PL emission intensity. The PL emission intensity of Ce3+ is higher in a REPO4 host with a lower site symmetry PO43- group (C2) than that with a higher site symmetry PO43- group (D2d). An increased disorder degree in Ce:GdxLu1-xPO4 mixed crystals leads to the shift of the 5d-level of Ce3+ towards a higher position, resulting in the blue shift of the PL emission wavelength. Moreover, the 5d → 4f emission of Ce3+ may also be modulated towards a larger wavelength via substituting the cation site with larger-radius cations under a particular crystallographic structure in REPO4. Our results highlight the importance of disordered local structures as well as activated anion groups in the enhanced PL emission of Ce3+ activators in a host lattice.