Exciton luminescence of boron nitride nanotubes and nano‐arches

Abstract

. The nanotube phase exhibits a broad-band PL near 380 nm, in agreement with a published report of cathodoluminescence from a sample comprising > 90% nanotubes. This emission is almost 3 eV lower in energy than unrelaxed exciton states found in recent all-electron theories of nt-BN and h-BN and about 1.4 eV lower than the lowest (perturbed dark?) exciton seen in absorption of nt-BN. This may suggest that excitons in nt-BN vibrationally relax to self-trapped states before emitting, a path found in many wide-gap solids, especially in quasi-1-dimensional forms. Exciton emission from bulk single-crystal h-BN has been shown to occur from vibrationally unrelaxed (free-exciton) states. We suggest a hypothesis in which known nano-arch reconstructions on the surface of h-BN may provide the low-dimensional environment to make exciton self-trapping on the surfaces of h-BN likely. This allows consistent interpretaton of the surface-related 380 nm emission from h-BN powder within a half-nanotube self-trapped exciton hypothesis.

Photoluminescence properties of pyrolytic boron nitride

“…This seems exclude a possibility of free carrier recombination on impurity, which is expected to be faster. Interestingly, a similar broad band around 3.15 eV has been observed in cathodoluminescence spectra of boron nitride nanotubes [31] and on photoluminescence on hBN powder [32]. Its appearance in hBN powder has been related to the luminescence of a strongly self trapped exciton on the edges of hBN micro crystals where dangling bonds can form nanoarches (half nanotubes) between neighbour sheets of BN [32].…”

Defect-induced blue luminescence of hexagonal boron nitride

“…The LWL is observed in PL and CL spectra of hBN materials with different origin by many authors [9,10,13,[17][18][19][20][21][22][23].…”

“…The following hBN materials were used for spectral investigation: i) hBN powder with average grain diameter 3 µm and purity of 99.5 % synthesized by Aldrich Corporation (M1), ii) hBN powder with grain diameter 5 µm and 98% purity obtained from NanoAmor Corporation (M2), iii) hBN powder with grain diameter 10 mkm and purity 99%, made by KOJUNDO Chemical Laboratory Co. LTD (M3), and iv) hBN nanomaterial consisting of multiwall nanotubes (MWBN) (M4) used in our previous investigation [17,18].…”

LOW-TEMPERATURE 450 nm LUMINESCENCE OF HEXAGONAL BORON NITRIDE

“…The 400 nm PL band exhibits a well resolved sub-band structure, whereas for the 450 nm band this substructure is resolved only weakly. The former (400 nm) PL band is analysed in our previous studies carried out at room temperature [15,16], whereas the latter (the 450 nm PL band) appears solely at low temperature and, therefore, in this study a special interest is mainly devoted to this band. Figure 2 shows the PLE spectra of bulk hBN powder at 8 K with a heavy curve for the 450 nm PL band.…”

“…therein). Our research group is also involved in this process and conducts research into the luminescence of bulk hBN powder and multiwall BN nanotubes (BNNTs) [14][15][16].…”