Achieving Fluorescent Colour Tunability in High-Luminescence MOF-76 via Hydrothermal Annealing and Lanthanide Ions Co-Doping

To date, most luminescence studies on MOF-76 have focused on tetragonal Tb 3+ -doped and Tb 3+ /Eu 3+ co-doped systems. In this work, MOF-76(Gd, Dy) and MOF-76(Gd, Tb, Dy, Eu) were synthesised for the first time and subsequently subjected to hydrothermal annealing in the presence of polyvinylpyrrolidone (PVP) as a dispersant. Annealing induced a tetragonal → monoclinic phase transition in MOF-76 and transformed the morphology from rods into highly crystalline, transparent nanosheets. As a result, the emission intensity of annealed MOF-76(Gd 0.98 , Dy 0.02 ) increased by approximately 25-fold and its photoluminescence quantum yield (PLQY) improved from 2.33% to 18.60%. These enhancements enabled the combination of hydrothermal annealing with a lanthanide co-doping strategy to achieve precisely tunable, highly luminescent colours in the multi-doped MOF-76(Gd, Tb, Dy, Eu) system. In the annealed materials ( a MOFs), efficient Tb 3+ → Dy 3+ and Dy 3+ → Eu 3+ energy transfer pathways were identified. Owing to their high luminescence and colour tunability, the resulting materials demonstrated practical applicability in colour-tunable fluorescent anti-counterfeiting and, when combined with N-CDs@starch, in white-light-emitting LED devices.