Rb₂HfCl₆:Sb³⁺ phosphors with tunable energy transfer for advanced information encryption and high-CRI WLEDs.

The realization of controllable multi-excitonic emission within a single-phase system remains a formidable challenge, yet it holds the key to advancing next-generation smart optoelectronics. Herein, we strategically engineer a dynamic energy transfer landscape in the zero-dimensional (0D) vacancy-ordered double perovskite Rb2HfCl6 by introducing Sb3+ dopants. In this 0D framework, the spatial isolation of [HfCl6]2- octahedron by Rb induces strong exciton localization, which provides a robust platform for efficient self-trapped exciton (STE) emission. By precisely tailoring the Sb3+ impurity levels, we established an excitation-wavelength-driven equilibrium between the host and dopant STEs. This synergistic modulation not only relaxes the Sb parity-forbidden transitions , elevating the photoluminescence quantum yield (PLQY) to 59%, but also enables a seamless switching of emission colors from green to orange-red under 254-365 nm excitation. Leveraging these unique optical signatures, we further demonstrate the material's potential in multi-level anti-counterfeiting smart locks and high-color-rendering white LEDs CRI = 90.2. This work underscores the power of excitonic state engineering in low-dimensional metal halides for the rational design of smart-responsive photonic materials.