Enhanced Nonlinear\nAbsorption, Refraction, and Optical\nLimiting Properties of CsPbI<sub>3</sub>/TiO<sub>2</sub> Nanocomposites\nfor Innovative Nonlinear Optical Devices

The investigation of nonlinear optical\n(NLO) properties\nis crucial\nfor the effective application of CsPbI<sub>3</sub>/TiO<sub>2</sub> nanocomposites in NLO devices. The CsPbI<sub>3</sub>/TiO<sub>2</sub> nanocomposites were synthesized by a hot injection method. Then,\nthe CsPbI<sub>3</sub>/TiO<sub>2</sub> nanocomposites were poured into\nmethyl methacrylate via polymerization to fabricate CsPbI<sub>3</sub>/TiO<sub>2</sub>/PMMA organic glasses (OGs). The crystal structure\nand size morphology of the CsPbI<sub>3</sub>/TiO<sub>2</sub> nanocomposites\nwere examined using X-ray diffraction (XRD) and transmission electron\nmicroscopy (TEM), respectively. The nonlinear absorption (NLA), nonlinear\nrefraction (NLR), and optical limiting (OL) properties of the CsPbI<sub>3</sub>/TiO<sub>2</sub>/PMMA OGs were investigated by using the Z-scan\ntechnique, employing a nanosecond pulse laser operating at a wavelength\nof 532 nm. The CsPbI<sub>3</sub>/PMMA and CsPbI<sub>3</sub>/TiO<sub>2</sub>/PMMA OGs can be transferred from saturable absorption (SA)\nto reverse saturable absorption (RSA) by varying the incident energy.\nIn addition, the CsPbI<sub>3</sub>/TiO<sub>2</sub>/PMMA OGs exhibit\nsuperior NLA, NLR, and OL performances compared to the CsPbI<sub>3</sub>/PMMA OG and other halide-based perovskites. The enhanced nonlinear\noptical (NLO) properties of CsPbI<sub>3</sub>/TiO<sub>2</sub>/PMMA\nOGs can be ascribed to the cooperative interaction between CsPbI<sub>3</sub> and TiO<sub>2</sub>. In summary, the results indicate that\nCsPbI<sub>3</sub>/TiO<sub>2</sub> nanocomposites possess substantial\npotential for applications in NLO devices such as optical limiters,\noptical switches, and optical modulators.