Enhanced circularly polarized photoluminescence and optical nonlinearity in oxygen-deficient Sm/Sr Co-Doped Bi5FeTi3O15/MO matrix

Sm 3 + /Sr 2+ -co-doped Bi 5 FeTi 3 O 15 (BFTO) nanocrystals were hydrothermally synthesized and embedded into a TeO 2 -based magneto-optical (MO) matrix using a melt-quenching technique. original BFTO nanocrystals exhibited 30–50 nm- hexagonal platelet-like morphology, which reduced to 20–35 nm after Sm 3+ /Sr 2+ doping due to lattice distortions and strain effects. The X-ray diffraction confirmed the crystal structure, while Raman and X-ray photoelectron spectra revealed charge redistribution and local asymmetry. Critically, Electron Paramagnetic Resonance analysis directly confirmed the presence of increased oxygen vacancies. These combined factors enhance the nonlinear optical (NLO) and chiroptical responses. The optimized 2 mol% Sm 3+ /Sr 2+ - Bi 5 FeTi 3 O 15 doped BFSS2 showed the highest third-order nonlinear susceptibility (χ (3) = 8.44 × 10 −11 esu), nonlinear refractive index (n₂ = 5.82 × 10 −10 m 2 /W), and nonlinear absorption coefficient (α 3 = 4.5 × 10 −11 m/W), demonstrating strong two-photon absorption (TPA) and Kerr nonlinearity. Photoluminescence spectra exhibited intense red emission at 610 nm and 645 nm, with BFSS2 achieving the highest circulary polarized luminescence (CPL) dissymmetry (g lum = −0.85) due to enhanced electric dipole –magnetic dipole interactions. Magnetic circularly polarized luminescence (MCPL) was significantly enhanced by Fe 2+ /Fe 3+ charge transfer and spin-orbit coupling. BFSS2 also exhibited the highest saturation magnetization (M s = 28 emu/g) and Verdet constant (28.3 rad/T·m at 633 nm), confirming strong magneto-chiral effects. These findings highlight the synergy of structural asymmetry, charge redistribution, and MO coupling in optimizing CPL, MCPL, and NLO properties, making BFSS2 a promising candidate for chiral photonic and magneto-optical applications.