Exceptional size-dependent property of TiS2 nanosheets for optical limiting

Highlights: • TiS₂ nanosheets showed exceptional size-dependent optical limiting property contrary to the reported TMDs nanosheets. • TiS₂ nanosheets with ultra-low normalized transmittance (as low as 12%) were developed. • The nonlinear absorption ways of TiS₂ can be regulated through bandgap engineering. • TiS₂/PMMA solid sample with a low initial threshold (0.03 J/cm²) and low optical threshold (0.57 J/cm²) was obtained. Transition metal dichalcogenides (TMDs), an emerging optical limiting material, exhibit excellent optical limiting properties for high energy laser. Generally, TMDs materials showed better laser protection with the decrease of lateral sizes. However, in this work, TiS₂ nanosheets showed exceptional lateral size-dependent optical limiting property contrary to the reported TMDs nanosheets. TiS₂ nanosheets with similar thickness and varied lateral sizes of 50 nm, 100 nm, 150 nm, 350 nm were obtained. Larger size TiS₂ nanosheets displayed better optical limiting performance and TiS₂ nanosheets with ultra-low normalized transmittance (as low as 12%) were developed. It was interesting to find that both two-photon absorption (TPA) and reverse saturable absorption (RSA) were exhibited in large TiS₂ nanosheets (350 nm) with a bandgap of 2.67 eV, while in small TiS₂ nanosheets (50 nm) with a bandgap of 3.51 eV, only TPA existed. Furthermore, the TiS₂ nanosheets incorporated polymethyl methacrylate (PMMA) sample with an extremely low content of 0.066 wt‰ TiS₂ nanosheets exhibited a low normalized transmittance of 18%, along with a low initial threshold (0.03 J/cm²) and low optical threshold (0.57 J/cm²), which showed great potential for practical use of the TiS₂ nanosheets in optical limiting field.