Recently, a lot of interest has been centred on the optical properties of hexagonal boron nitride (h‐BN), which has a similar lattice structure to graphene. Interestingly, h‐BN has a wide bandgap and is biocompatible, so it has potential applications in multiphoton bioimaging, if it can exhibit large nonlinear optical (NLO) properties. However, extensive investigation into the NLO properties of h‐BN have not been done so far. Here, NLO properties of 2D h‐BN nanosheets (BNNS) are reported for the first time, using 1064‐nm NIR laser radiation with a pulse duration of 10 ns using the Z‐scan technique. The reverse saturable absorption occurs in aqueous colloidal solutions of BNNS with a very large two‐photon absorption cross section (σ 2PA) of ≈57 × 10−46 cm4 s−1 photon−1. Also, by using UV–Vis absorption spectroscopy, the temperature coefficient of the bandgap (dE g/dT) of BNNS is determined to be 5.9 meV K−1. Further defect‐induced photoluminescence emission in the UV region is obtained in the 283–303 K temperature range, under excitations of different wavelengths. The present report of large σ 2PA combined with stability and biocompatibility could open up new possibilities for the application of BNNS as a potential optical material for multiphoton bioimaging and advanced photonic devices.

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Recently, there has been a renaissance in theoretical and experimental studies on 2D heterostructures of two 2D wonder materials, namely graphene and hexagonal boron nitride (hBN) having plethora of application potentials in fundamental research as well as in developments of new technological devices. However, the nonlinear optical (NLO) property of hexagonal boron nitride nanosheets−graphene oxide (BNNS−GO) heterostructure has hitherto remained unexplored. Here, in this work NLO properties of BNNS−GO have been reported, for the first time, in the visible region by Z-scan technique in nanosecond regime. Nonlinear absorption coefficient (β 2PA ) and third order nonlinear susceptibility (χ 3 ) of BNNS−GO have been found to be enhanced significantly by 13.4% and 21.7%, respectively in compared to those of bare BNNS. The synthesized heterostructure is showing a superior optical limiting property as compared to that of bare BNNS. The change in polarizabilities of GO sheets with the insertion of hBN in its framework, formation of donor−acceptor pair and bandgap narrowing effects have caused the enhancement in NLO properties of BNNS−GO heterostructure. Temperature dependent photoluminescence (PL) of BNNS−GO have been conducted in 278−303 K temperature range and observed Arrhenius type variation of PL intensity with temperature. Thus, it is envisioned that this work will open new vistas of applications of 2D BNNS−GO heterostructure materials in developing photonic safety devices of eye to be used in military and in other industries.

Enhanced (by ∼2.8) nonlinear optical property of GO–Ag nanocomposite has been reported by Z-scan technique at a visible wavelength of 532 nm. The synthesized GO–Ag nanocomposite is also displaying significant optical limiting effect.