Exploring Double Luminescence in Bi3+-Doped Cs2ZrCl6 Perovskite Crystals: Insight into Multiexcitonic Emission Processes for Optoelectronic Applications

Metal halide perovskites show promise for lighting applications, but their multiexcitonic emission processes are not fully understood. This study delves into the multiexcitonic emission processes in metal halide perovskites to enhance our understanding of their optical properties and potential for lighting technologies. Specifically, this study focuses on the optical properties of Bi³⁺ doped Cs₂ZrCl₆ lead-free perovskite crystals, showcasing their potential for optoelectronic applications. The crystals were synthesized using a solvothermal method with varying Bi³⁺ concentrations. X-ray diffraction (XRD) analysis showed the structural parameters of the perovskite. The material had a truncated octahedron morphology, as confirmed by scanning electron microscopy (SEM). Optical studies revealed UV absorption and a decrease in the band gap energy to 2.6 eV for 10% Bi³⁺ doping, indicating the integration of Bi³⁺ ions into the lattice. The crystals displayed dual luminescence from host self-trapped excitons (STEs) and dopant-induced STEs. Bi³⁺ doping led to the emission of blue triplet STEs, demonstrating the tunability of luminescence with dopant concentration. Both pristine and Bi³⁺ doped crystals emitted light at 254 nm, which is attributed to the ¹S₀ → ³P₁, while only the Bi³⁺ doped crystals emitted light at 365 nm. The presence of Bi³⁺ ions led to multiple excitonic peaks in the photoluminescence excitation spectra, resulting in blue emission at 450 nm. The emission intensity was directly related to the Bi³⁺ concentration when excited at 350 nm. The broad emission band, with a substantial Stokes shift of 195 nm, is attributed to STEs induced by strong electron–phonon coupling. Additionally, emission at 450 nm in the Bi³⁺ doped crystal suggests the presence of another transition (³P₁ → ¹S₀) while excited at 257 and 350 nm. Our results offer insights into the emissive mechanism induced by Bi³⁺ ion doping in nS² and suggest ways to enhance luminescence efficiency for future applications.