Owning many peculiar properties, hexagonal boron nitride nanosheets (BNNSs) have lots of potential applications, such as electronic devices and deep ultraviolet emitters. In this article, a chemical exfoliation method to prepare few-layer and large size BNNSs is reported. Through related instrument characterizations, we demonstrated that this preparation method can allow the exfoliation of BNNSs from bulk BN powder successfully. From CL spectra, the as-prepared BNNSs were proved to show stronger CL emission ability than BN powder. Based on the experiment results analysis, we proposed an exfoliation mechanism and verified it through in situ SEM detection.

High-quality graphene sheets with lateral size over $20\mathrm{\mu m}$ have been obtained by bath sonicating after subjecting the wormlike graphite marginally to mixed oxidizer. To date, to our knowledge, they are the largest graphene sheets prepared by exfoliation in the liquid phase. A saturable absorber mirror was fabricated based on these sheets. We exploited it to realize mode-locking operation in a diode-pumped $\mathrm{Nd}\text{:}{\mathrm{GdVO}}_4$ laser. A pulse duration of $16\mathrm{ps}$ was produced with an average power of $360\mathrm{mW}$ and a highest pulse energy of $8.4\mathrm{nJ}$ for a graphene mode-locked laser.