Efficient Tuning of Blue-to-Cyan-Green Emission in Bismuth(III)-Doped Alkaline-Earth Aluminates via Crystal Site Engineering

The development of emission-tunable phosphors is crucial for advancing high-performance phosphor-converted white light-emitting diodes (PC-WLEDs). Here, we report a novel aluminates blue phosphor, Sr2LaAlO5:Bi3+, which exhibits a peak emission wavelength of 448 nm under ultraviolet excitation. Structural and spectroscopic studies indicate the presence of multiple luminescent centers in Sr2LaAlO5:Bi3+. Using the cation-equivalent substitution strategy, we further constructed a series of solid-solutions, Sr2–yBayLaAlO5:Bi3+ (0 ≤ y ≤ 2), and achieved continuous emission tuning from blue (448 nm) to cyan-green (494 nm) via Ba2+ substitution. Rietveld refinements of XRD data demonstrate that Ba2+ preferentially occupies the Sr2O10 site with a large coordination number, inducing a consequent red-shift in the emission spectra. The red-shift is rationalized by the synergistic effects of crystal field splitting, Stokes shift, and the nephelauxetic effect. By integrating the blue phosphor Sr2LaAlO5:0.03 Bi3+, the cyan-green phosphor Ba2LaAlO5:0.03 Bi3+, and the red phosphor CaAlSiN3:Eu2+ on a 360 nm LED chip, a pc-WLED with high brightness, an outstanding color rendering index, and a low correlated color temperature was demonstrated. This study offers valuable design insights into modulating the host lattice coordination environment to achieve tunable luminescent colors in Bi3+-doped phosphors.