Fabrication of Broadband Warm-Cool Tunable White-Light-Emitting Cs ₂ Na _<i>x</i> Ag _{1– <i>x</i>} InCl ₆ :Bi Perovskite NCs by Component Engineering and NH ₃ -Induced Phase Transition

White light-emitting sources have attracted widespread attention for their high efficiency, remarkable tunability, and luminous qualities comparable to natural light. Among them, white light-emitting materials with high stability and tunability are essential for practical lighting applications. Herein, a wide range of warm-to-cool white light regulation was achieved through two distinct approaches: component engineering and the NH₃-induced phase transition. A series of lead-free perovskite Cs₂Na_<i>x</i>Ag_1-<i>x</i>InCl₆:Bi (<i>x</i> = 0, 0.2, 0.4, 0.6, 0.8, 1.0) nanocrystals (NCs) have been synthesized. As the Na/Ag ratio increased, the correlated color temperature (CCT) increased from 3199 K for warm white and from 9636 K for cool white. Furthermore, Cs₂AgInCl₆:Bi NCs demonstrated a specific response to NH₃. In an ammonia-rich environment, the NCs transitioned from emitting warm white light to emitting cool white light. When the NCs were exposed to HCl gas, they gradually reverted from cool white light to warm white light. Both approaches offer a wide tuning range from warm to cool white light, providing effective strategies for customizing LED devices to meet specific lighting needs.