Mo⁴⁺-Doped Cs₄ZnBi₂Cl₁₂ Lead-Free Double Perovskite for Near-Infrared Luminescence

This study presents the synthesis of Mo⁴⁺-doped Cs₄ZnBi₂Cl₁₂ double perovskite through a hydrothermal method, demonstrating efficient near-infrared (NIR) emission at 1110 nm with a full width at half maximum (FWHM) of 45 nm. The emission originates from the d-d transition of Mo⁴⁺ ions within an octahedral crystal field. Structural analysis using powder X-ray diffraction (PXRD) confirms the phase purity and lattice contraction as a result of Mo⁴⁺ substitution at Bi³⁺ sites, supported by X-ray photoelectron spectroscopy (XPS) and elemental mapping. The material exhibits broad excitation compatibility (348-590 nm) and achieves a photoluminescence quantum yield (PLQY) of 45.3% with a microsecond-scale lifetime of 6.78 μs. Thermal stability tests demonstrate sustained emission intensity (58% at 420 K) and resilience to prolonged heating or UV exposure. This work highlights Mo⁴⁺-doped Cs₄ZnBi₂Cl₁₂ as a stable and efficient NIR emitter, advancing lead-free perovskites for optoelectronic applications in bioimaging, agriculture, and sensing.