Exciton relaxation modulation and lattice distortion in Rb₄CdCl₆:Sn²⁺/Bi³⁺ toward tunable white-light and optical...

Metal halides with tunable local electronic states and excellent optical properties are indispensable for achieving single-component multi-color luminescence and solid-state healthy lighting. However, the precise regulation of dark self-trapped excitons (STEs) remains a critical challenge in achieving high-performance luminescence. This work employed zero-dimensional (0D) Rb₄CdCl₆ as the host to systematically investigate the spectral characteristics and underlying mechanisms of Sn²⁺ single-doped, Bi³⁺ single-doped, and Sn²⁺/Bi³⁺ co-doped samples. The results indicate that Sn²⁺ ions lead to the emission of blue bright STEs, while the introduction of Bi³⁺ effectively activates low-energy (LE) dark STEs through local lattice distortion and energy level regulation, thereby achieving the transition from single-band blue light to dual-band spectra. Sn²⁺ ions are the main luminescent centers, while Bi³⁺ ions stabilize dark-state emission by regulating exciton relaxation pathways and forming SnBi pairs. The synergistic effect of bright/dark STEs enables controllable cold-to-warm white emission and information anti-counterfeiting applications, providing new strategies for designing high-performance single-component luminescent halides via lattice strain engineering.