  Low-dimensional wide bandgap semiconductors open a new playing field in
quantum optics using sub-bandgap excitation. In this field, hexagonal boron
nitride (h-BN) has been reported to host single quantum emitters (QEs), linking
QE density to perimeters. Furthermore, curvature/perimeters in transition metal
dichalcogenides (TMDCs) have demonstrated a key role in QE formation. We
investigate a curvature-abundant BN system - quasi one-dimensional BN nanotubes
(BNNTs) fabricated via a catalyst-free method. We find that non-treated BNNT is
an abundant source of stable QEs and analyze their emission features down to
single nanotubes, comparing dispersed/suspended material. Combining high
spatial resolution of a scanning electron microscope, we categorize and
pin-point emission origin to a scale of less than 20 nm, giving us a one-to-one
validation of emission source with dimensions smaller than the laser excitation
wavelength, elucidating nano-antenna effects. Two emission origins emerge:
hybrid/entwined BNNT. By artificially curving h-BN flakes, similar QE spectral
features are observed. The impact on emission of solvents used in commercial
products and curved regions is also demonstrated. The 'out of the box'
availability of QEs in BNNT, lacking processing contamination, is a milestone
for unraveling their atomic features. These findings open possibilities for
precision engineering of QEs, puts h-BN under a similar 'umbrella' of TMDC's
QEs and provides a model explaining QEs spatial localization/formation using
electron/ion irradiation and chemical etching.
