Giant two-photon absorption in MXene quantum dots
Hao Wei, Yiduo Wang, Yingwei Wang, Wenxuan Fan, Li Zhou, Mengqiu Long, Si Xiao, Jun He
Abstract
Looking for materials with compelling nonlinear optical (NLO) response is of great importance for next-generation nonlinear nanophotonics. We demonstrate an escalated two-photon absorption (TPA) in ultrasmall niobium carbide quantum dots (Nb 2 C QDs) that is induced by a two-even-parity states transition. The TPA response of Nb 2 C QDs was observed in the near-infrared band of 1064–1550 nm. Surprisingly, at 1064 nm, Nb 2 C QDs shows an enhanced TPA response than other wavelengths with a nonlinear absorption coefficient up to a value of 0.52 ± 0.05 cm/GW. Additionally, the nonlinear optical response of Nb 2 C changes to saturable absorption when the incident wavelength is between 400–800 nm wavelength. Density functional theory (DFT) validates that TPA, induced by two even-parity states transition, breaks the forbidden single-photon transition, enabling a tremendous TPA response in Nb 2 C QDs at 1064 nm. It offers the possibility of manipulating the NLO response of Nb 2 C via morphology or surface termination.