Bilayer Spectral Engineering of Bi ^{3 +} /Te ^{4 +} ‐Doped Cs _{2 Yanmei Chen, Christopher Dzorkpata, Hongyang Zhu, Azmin Islam, Somayeh Saadat Niavol, Andrew C. Meng, Peifen Zhu}

ABSTRACT

Lead‐free vacancy‐ordered double perovskites are promising phosphors for solid‐state lighting, yet achieving white‐light emission with simultaneously high color fidelity, tunable correlated color temperature (CCT), and controllable circadian‐relevant optical response remains challenging. Here, we demonstrate bilayer spectral engineering of Bi ^{3 +} /Te ^{4 +} ‐doped Cs ₂ ZrCl ₆ phosphors for human‐centric white light‐emitting diodes (WLEDs). A concentrated HCl‐assisted powder conversion (HAPC) method enables room‐temperature synthesis of Bi ^{3 +} ‐ and Te ^{4 +} ‐doped Cs ₂ ZrCl ₆ microcrystals with complementary broadband emission. Pristine Cs ₂ ZrCl ₆ shows intrinsic blue self‐trapped exciton emission near 430 nm, whereas Bi ^{3 +} and Te ^{4 +} dopants introduce blue and broadband yellow emission centered near 465 and 575 nm, respectively. Stacked bilayer color‐conversion layer (CCL) architectures based on Cs ₂ ZrCl ₆ :5%Bi and Cs ₂ ZrCl ₆ :1%Te redistribute the blue and yellow components through layer‐thickness control, enabling CCT tuning from 3164 to 4895 K. An optimized WLED achieves CIE coordinates of (0.395, 0.363), a color rendering index (CRI, R _a ) of 93.4, a TM‐30 fidelity index (R _f ) of 93.8, gamut index (R _g ) of 99.8, and a luminous efficacy of radiation (LER) of 228 lm W ^{− 1} . Photoreceptor‐weighted analysis further shows the melanopic response can be tuned while maintaining high color quality, establishing Bi ^{3 +} /Te ^{4 +} ‐engineered Cs ₂ ZrCl ₆ bilayers as a rare‐earth‐free platform for spectrally tunable, high‐fidelity, circadian‐relevant solid‐state lighting.