Structural and Photoluminescence Properties of Ba3Y1– z Lu z Al2O7.5: Bi3+/Bi3+,Eu3+ Phosphors for WLEDs Applications

Bi3+-doped and Bi3+/Eu3+-codoped Ba3Y1–zLuzAl2O7.5 phosphors with different compositions were prepared via a high-temperature solid-state route, followed by systematic evaluation of their crystal structure, luminescence characteristics, energy transfer process, and temperature-dependent emission behavior. Under 323 nm near-ultraviolet excitation, Ba3YAl2O7.5: Bi3+ exhibits a broad yellow emission centered at 555 nm. Upon Eu3+ codoping, characteristic orange-red Eu3+ emission is introduced, producing a broad emission band spanning approximately 550–750 nm. Spectral overlap and fluorescence lifetime measurements confirm energy transfer from Bi3+ to Eu3+, with a maximum transfer efficiency of 35.66% at 7% Eu3+. Partial substitution of Y3+ by Lu3+ provides effective regulation of the local crystal environment. With increasing Lu3+ content, the Bi3+ emission peak gradually red-shifts from 555 to 577 nm, accompanied by improved thermal stability. For the optimized Ba3Y0.5Lu0.5Al2O7.5:2% Bi3+,3% Eu3+ phosphor, the Bi3+ and Eu3+ emission intensities retain 76% and 72% of their room-temperature values at 423 K, respectively. By combining the optimized phosphor with a commercial blue-emitting phosphor and a near-ultraviolet LED chip, a WLED was constructed, delivering an Ra value of 87 and a CCT of 4822 K. Moreover, the device maintains a largely unchanged spectral profile from 300 to 425 K. These results demonstrate that the combined Bi3+→Eu3+ energy transfer and Lu3+-substitution strategies provide an effective route for color tuning and thermal-stability improvement in phosphors for high-quality white-light applications.