Nonlinear Optical Properties of Cs3BiBr6 Nanocrystals Doped with SbBr3: From Experimental Observation to Theoretical Calculations

The nonlinear optical (NLO) properties of lead-free halide perovskites are of significant interest for photonic applications, yet strategies for compositional engineering remain limited. In this work, SbBr3-doped Cs3BiBr6 nanocrystals (Cs3BiBr6/SbBr3) were prepared using a hot-injection synthesis method and subsequently embedded in poly(methyl methacrylate) (PMMA) to fabricate organic glass (OGs). X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses confirmed that the materials exhibited high phase purity along with a uniformly dispersed nanoscale structure. Z-scan measurements using a 532 nm nanosecond laser demonstrated that Cs3BiBr6/PMMA matrix displayed a NLO response, shifting from saturable absorption (SA) to reverse saturable absorption (RSA). Whereas Cs3BiBr6/SbBr3/PMMA showed dominant RSA with enhanced optical limiting (OL) performance. The effective nonlinear absorption coefficient (β) decreased from 2.10×10-8 to 1.35×10-8 mW-1 with increasing excitation energy, highlighting the role of Sb incorporation in strengthening RSA. First-principles calculations revealed stable integration of Sb into the perovskite lattice, narrowing the bandgap and introducing Sb states near the Fermi level, thereby enhancing light–matter interactions. These results demonstrate that Sb-doped Cs3BiBr6 is a promising lead-free perovskite for advanced NLO devices such as optical switches and optical limiters.