Tunable Optical Properties and Increased Thermal Quenching in the Blue-Emitting Phosphor Series: Ba2(Y1–xLux)5B5O17:Ce3+ (x = 0–1)

The preparation of cerium-substituted barium lutetium borate, Ba 2 Lu 5 B 5 O 17:Ce 3+, is achieved using high temperature solid state synthesis. This compound crystallizes in the Ba 2 Y 5 B 5 O 17 -type structure and shows an efficient blue emission (λ max = 447 nm) when excited by UV-light (λ ex = 340 nm) with a photoluminescent quantum yield near 90%, a fast luminescence decay time (<40 ns), and a thermal quenching temperature of 452 K. Further, preparing a solid solution following Ba 2 (Y 1– x Lu x ) 5 B 5 O 17:Ce 3+ ( x = 0, 0.25, 0.50, 0.75, 1) confirms that all compounds are isostructural and follow Vegard’s law. Substituting Y 3+ for Lu 3+ yields a nearly constant emission spectrum that blue-shifts by only 9 nm and has a consistent luminescence lifetime across the range prepared. The photoluminescent quantum yield (PLQY) and thermal quenching ( T 50 ) of the solid solution, however, are dramatically impacted by the composition, with the PLQY decreasing to ≈70% and the T 50 dropping 49 K going from x = 1 to x = 0. These significant changes in the optical properties likely stem from enhanced structural rigidity as the larger, more polarizable Y 3+ is substituted for the smaller, harder Lu 3+ cation. These results highlight the importance of optimizing chemical bonding to improve a phosphor’s optical properties.