Nonlinear Optical Properties and Temperature‐Dependent UV–Vis Absorption and Photoluminescence Emission in 2D Hexagonal Boron Nitride Nanosheets

Abstract

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.

Defect‐Based Modulation of Optoelectronic Properties for Biofunctionalized Hexagonal Boron Nitride Nanosheets

“…For the pristine h‐BNNF surface, a UV/Vis absorption was observed at approximately 186 nm, corresponding to an electronic transition from the π orbital of a N atom to the π* orbital of a B atom (HOMO→LUMO) of the nanoflake (Table S3), which is in reasonable agreement with the absorption energy (≈200 nm) value for a different flake‐sized h‐BNNF . This peak is consistent with the UV absorbance peak of 203 nm for boron nitride sheets experimentally observed by Ajayan and co‐workers and theoretically reported by Vovusha et al …”

Facile synthesis, microstructure and photophysical properties of core-shell nanostructured (SiCN)/BN nanocomposites

“…Wu et al . also observed BN nanotubes and BNNSs with broad PL emission bands at 4.2 and 6.05 eV, respectively959. Further, PL emission at 5.46 eV has been attributed to the radiative recombination of donor-acceptor pair transition.…”

“…Such heterostructures are known for the induction of a strong internal electric field18. These results suggest that SiC(N)/BN nanocomposites might be excellent candidates for both optoelectronic and electronic applications9.…”

“…In particular, SiC and BN semiconductor nanocrystals have enabled and transformed research in technologically important areas including biolabeling789, microelectromechanical (MEMS) and optoelectronic devices101112. For example, emission wavelengths can now be precisely controlled by the nanostructure composition, the average grain size and the formation of core-shell structures4131415.…”

“…Herein, we pyrolysis polyborosilazane precursors containing the facilely synthesized cobalt complex [Co (en) 3 ]·Cl 3 which appears to catalyze the formation of SiC(N) nanowires as well as the contribution to enhance the fluorescence. This method should pave the way for 2D BNNSs loading SiCN/BN heterostructure production and utilization as functional fluorescence for a wide range of biolabeling, photonics1235, and optoelectronic devices930.…”