Giant two-photon absorption in MXene quantum dots

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 (Nb2C QDs) that is induced by a two-even-parity states transition. The TPA response of Nb2C QDs was observed in the near-infrared band of 1064-1550 nm. Surprisingly, at 1064nm, Nb2C 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 Nb2C 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 Nb2C QDs at 1064nm. It offers the possibility of manipulating the NLO response of Nb2C via morphology or surface termination. (C) 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

Automated summary

The search for materials with compelling nonlinear optical (NLO) response is crucial in the field of next-generation nonlinear nanophotonics. In this study, we demonstrate an enhanced two-photon absorption (TPA) in ultrasmall niobium carbide quantum dots (Nb2C QDs) induced by a two-even-parity states transition. The TPA response of Nb2C QDs was observed in the near-infrared band of 1064-1550 nm. Surprisingly, Nb2C QDs showed an enhanced TPA response at 1064nm compared to other wavelengths, with a nonlinear absorption coefficient of 0.52 +/- 0.05 cm/GW. Moreover, the nonlinear optical response of Nb2C changed to saturable absorption when the incident wavelength was between 400-800 nm. Density functional theory (DFT) confirmed that the TPA response in Nb2C QDs at 1064nm was due to the breaking of forbidden single-photon transition by the two-even-parity states transition. This discovery opens up possibilities for manipulating the NLO response of Nb2C through morphology or surface termination.