Dynamic Color-Tunable Luminescence in Lead-Free Perovskites by Asymmetric Energy Transfer and Excitation-Dependent Dual Self-Trapped Excitons Emission

Abstract

Lead-free halide perovskites have garnered significant interest as eco-friendly alternatives to lead-based optoelectronic materials, yet achieving tunable self-trapped exciton (STE) emission with high efficiency and stability remains challenging. Herein, we report a Bi3+/Te4+ co-doped Rb2SnCl6 perovskite system that enables excitation-dependent dual-band STE emission. Through a modified thermal precipitation method, Bi3+ and Te4+ dopants were successfully incorporated into the Sn4+ lattice sites, inducing localized lattice distortions while preserving the cubic host framework. Structural and chemical analyses confirm homogeneous dopant distribution and stable oxidation states. The Bi3+-related STE emission (445 nm, blue) and Te4+-related STE emission (560 nm, orange) exhibit distinct excitation-dependent responses, governed by selective activation of dopant-specific electronic transitions and competitive energy transfer pathways. Transient spectroscopy reveals asymmetric energy transfer efficiencies of 46.9% (Te4+ → Bi3+) and 4.3% (Bi3+ → Te4+), attributed to dopant concentration gradients and electron-phonon coupling strength disparities. By optimizing Bi3+/Te4+ ratios, the system achieves tunable CIE coordinates from deep blue (0.15, 0.09) to orange (0.41, 0.53), with a balanced white-light emission (0.29, 0.32) at 360 nm excitation. The co-doped perovskite demonstrates a maximum photoluminescence quantum yield (PLQY) of 58% and robust thermal stability, retaining 15% emission intensity at 300 K. Fabricated UV-pumped white LEDs exhibit stable color rendering (CRI = 82) across operating currents (10-80 mA), highlighting its potential as a single-component phosphor. This work provides a strategic approach for engineering excitation-responsive STE dynamics in lead-free perovskites for advanced optoelectronic applications.

Keywords: Lead-free Perovskites, Asymmetric Energy Transfer, White LED, Self-trapped Excitons Emission