Photoluminescence Emission Studies on a Lanthanum-Doped Lead Free Double Halide Perovskite, La:Cs2SnCl6

Recent advances in bandgap engineering have increased the possibility of vacancy ordered double halide perovskites (VO-DHPs), Cs₂SnX₆ where X = Cl, Br, I with designable optoelectronic features. Doping with La³⁺ ions modulates the band gap from 3.8 to 2.7 eV, allowing a steady room temperature dual emission (PL) centered at 440 and 705 nm in Cs₂SnCl₆. Pristine Cs₂SnCl₆ and La:Cs₂SnCl₆ both have a crystalline cubic structure with a space symmetry of Fm3m. The cubic phase correlates well with the Rietveld refinement. SEM analysis confirms anisotropic development with huge micrometer-sized (>10 μm) truncated octahedral structures. DFT investigations show that the insertion of La³⁺ ions into the crystal lattice leads to the band splitting. The present study elaborates the experimental understanding of the dual PL emission properties of La:Cs₂SnCl₆ leaving a scope for detailed theoretical study on the origin of the complex electronic transitions involving f-orbital electrons.