Investigation of Photoluminescent Characteristics in Bismuth-Doped Cs₃Mo₂Cl₉ Halide Perovskite: Implications for Light Emission Mechanisms

This study presents the successful synthesis of Bi3+ doped Cs3Mo2Cl9, a lead-free vacancy-ordered halide perovskite, via a solvothermal method, for optoelectronic applications. Structural analysis using X-ray diffraction (XRD) confirmed the crystalline nature of the synthesized material, exhibiting a hexagonal phase with space symmetry P63/mmc. Optical absorption studies indicate the activity of material in the UV region, with absorption at approximately 350 nm and a calculated bandgap energy value of ∼3.54 eV through wood and the Tauc equation for the 5% Bi3+ doped Cs3Mo2Cl9 vacancy-ordered halide perovskite. Photoluminescence excitation spectra (PLE) exhibited a broad band centered at ∼360 nm, consistent with the 1S0 → 3P1 (A band) transition for 5% Bi3+ doped Cs3Mo2Cl9. Contrasting with no emission from the pristine material, PL analysis revealed consistent emissions at ∼447 nm upon Bi3+ ion incorporation with the full width at half-maximum (fwhm) of ∼49 nm under various excitation wavelengths. The emission is attributed to the 3P1 → 1S0 transition for all Bi3+ doped Cs3Mo2Cl9 vacancy-ordered perovskite. Photoluminescence quantum yield (PLQY) demonstrated a pronounced dependence on Bi3+ concentration, reaching a maximum of 8.5% at the optimal 5% doping level before decreasing to 6% at 10% due to concentration quenching, as explained by the Blasse equation. This highest PLQY at 5% doping signifies an optimal balance between defect passivation and suppression of nonradiative pathways. Critically, this material exhibits exceptional environmental stability retaining >95% of its initial photoluminescence intensity and structural integrity under ambient conditions for >90 days. These findings highlight the potential of Bi3+ doped Cs3Mo2Cl9 perovskite with an optimized doping level for diverse optoelectronic applications, suggesting avenues for further exploration in light-emitting diodes (LED) technology, photovoltaics, and sensor development.