Photoluminescence excitation spectroscopy in boron nitride nanotubes compared to microcrystalline h‐BN and c‐BN

Abstract

PACS 78.67.-n Photoluminescence spectra and photoluminescence excitation spectra have been measured on samples of hexagonal boron nitride microcrystalline powder, cubic boron nitride single crystal, and boron nitride nanotubes (mixture of single-walled and multi-walled with some h-BN precursor). The reason for studying these 3 samples in a comparative fashion is that nanotube BN, while based on a rolled hexagonal-BN (sp 2 -bonded) sheet, is expected to take on more sp 3 bond-character reminiscent of cubic-BN as the curvature becomes tighter. With some simplicity of statement, this study was planned to view spectroscopy of nanotube BN with respect to its two limiting cases of bond character, all measured in the same apparatus. Because of the mixed character of presently available BN nanotube samples, we consider it important to measure not just the luminescence spectra, but the tuneable-uv excitation spectra, and thereby hope to make connection with the band gaps and distinguish possible defect or impurity features.

Defect-related photoluminescence of hexagonal boron nitride

“…1 have been recently reported on photoluminescence and cathodoluminescence experiments of commercial hBN powder. 10,[39][40][41][42][43][44][45][46][47][48] However, in these publications, no distinctions were made between the broad band and structured emissions. We now assign the structured UV emission to impurities ͑probably C͒ and the broadband emission to deep DAP of strongly localized center.…”

“…1͑a͒ and 1͑b͔͒ has been reported in the past by numerous groups either in 10,43,46,47 or photoluminescence experiments. 10,14,[39][40][41][42]44,45,47,48 Some authors have assigned it to intrinsic luminescence of hBN molecular layers 47 or to phonon-assisted band-edge luminescence. 42 However, recent experiments 1 and theoretical calculations 34 indicate the hBN band-gap energy in the range from 6 to 6.5 eV that disables these interpretations.…”

Optical properties of multiwall boron nitride nanotubes

“…Some optical experiments have been performed on BNNT at a macroscopic scale and confirm in part the theoretical results. First, photoluminescence and cathodoluminescence measurements performed on MWBNNT revealed the existence of a luminescence band around 4 eV [17][18][19][20] whereas optical absorption measurements of a macroscopic SWBNNT sample showed two absorption bands in the UV range centered at 4.4 eV and 5.5 eV [21].…”

Exciton luminescence of boron nitride nanotubes and nano‐arches

“…In a preliminary report, we compared the PL and PL-excitation of cubic-BN, hexagonal-BN and the nt-BN/h-BN mixture [3]. The excitation spectroscopy was crucial in distinguishing features that corresponded with a charac-teristic h-BN PL signature from those possibly assignable to the nanotube phase.…”