Excitation‐Dependent Thermal Behavior of a New Type of Phosphors Ba 1‐x Sr 1+x Y ₄ O ₈ :Ce ³⁺

A major bottleneck hindering the advancement of high‐quality white light‐emitting diodes (WLEDs) is the thermal quenching of phosphors. Here, we report a series of cyan‐green phosphors Ba 1‐x Sr 1+x Y 4 O 8 :Ce 3+ in which precise control over the emission peak position and a significant enhancement in luminescence thermal stability are achieved through crystal field engineering. The luminescence intensity at 423 K increased from 46.8% at room temperature (BaSrY 4 O 8 :0.002Ce 3+ ) to 69.9% (SrY 2 O 4 :0.002Ce 3+ ). More importantly, the SrY 2 O 4 :0.002Ce 3+ phosphor exhibits unique anti‐thermal quenching behavior under specific excitation wavelengths. When excited at 340 nm, its emission intensity at 423 K reaches 123% of the room‐temperature value. The phenomenon is mainly attributed to the existence of the deep trap level in SrY 2 O 4 :0.002Ce 3+ . Finally, a warm WLED device with a color rendering index (CRI) of 90.55 and a correlated color temperature (CCT) of 4149 K was successfully prepared by combining the phosphor with commercial blue and red phosphors, which has a good application prospect. Furthermore, owing to its outstanding high‐temperature luminescence stability, this series of phosphors can be further extended to emerging fields such as fingerprint recognition and information storage and encryption in high‐temperature environments.