Quenching of Defect-Induced Photoluminescence in a Boron-Nitride and Carbon Hetero-nanotube

Using a 266 nm laser, we simultaneously observe Raman and photoluminescence (PL) spectra of vertically aligned boron-nitride nanotubes (VA-BNNT) and single-walled carbon nanotubes (SWNT) encapsulated by boron nitride (VA-SWNT@BNNT). The larger PL intensity in VA-BNNT compared to that of the h-BN single crystal suggests that VA-BNNT contains more defect states. VA-SWNT@BNNT exhibits two multiphonon Raman peaks at 3033 and 3142 cm^-1 and four PL peaks at 4639, 5859, 6905, and 8293 cm^-1. Notably, the PL intensity of VA-SWNT@BNNT is 20 times smaller than that of VA-BNNT. In VA-SWNT, we observe an additional Raman peak at 4677 cm^-1, which closely aligns with the 4639 cm^-1 PL peak of VA-SWNT@BNNT, suggesting photoexcited electrons in VA-BNNT may transfer to the Raman process within VA-SWNT component of VA-SWNT@BNNT. The first-principles calculations identify possible donor and acceptor states in BN bilayers with substitutional defects (e.g., carbon replacing boron or nitrogen). These defect states are also relevant to understanding the origin of PL in BNNT.