Determination of the optical bandgap of the Bernal and rhombohedral boron nitride polymorphs

Polytypes of sp2-Bonded Boron Nitride

“…Another sample was grown in which 5% vanadium was added to the Cr + Ni eutectic solvent. Both samples grown with Cr + Ni + C and Fe + V exhibited Bernal-related PL, as we shall see later, but in contrast to the X-ray spectrum of the former, the latter did not contain misoriented polymorphic inclusions [136]. However, its X-ray diffraction spectrum is not as good as those of a high-quality hBN sample.…”

“…Note that it is worthwhile attributing the 6.035 eV luminescence to the recombination at the bottleneck of the lowest polariton branch of the direct exciton polariton systems; thus, the value of the excitonic gap is higher than this value by an amount dictated by the magnitude of the longitudinal-transverse (LT) splitting between the branches of dispersion of the exciton-polariton. This LT splitting is huge in hBN [119], about 400 meV, and from the band structure calculations referenced above [57,62,[121][122][123][124][125][127][128][129][130][131][132][133]136,137], there is no reason for it to be drastically different in bBN.…”

“…The 8 K macro-photoluminescence spectra in the 5-6.1 eV range of several samples showing the phonon-assisted transitions typical of hexagonal boron nitride (hBN; blue spectrum), mixed with the undulations linked to rBN and bBN inclusions impurities (green and red spectra). The signature of the direct bandgap of bBN is detected by a peak at 6.035 eV, following[136].…”

Tuning colour centres at a twisted hexagonal boron nitride interface

“…As a result, more CN simply leads to more VN due to the balancing of charges to make the whole system charge-neutral. The rigorously controlled carbon doping experiments 47 and isotopically controlled carbon doping experiments 48 of hBN suggest that the 4.1-eV peak and its PSB are independent of the carbon atoms. (2) In our ab initio GW calculations, we assume a fixed lattice for the ground and excited electronic states, which essentially ignores the electronphonon coupling.…”

Bernal Boron Nitride Crystals Identified by Deep-Ultraviolet Cryomicroscopy

“…The sample studied is a polytypic sp 2 -bonded carbon-doped BN crystal precipitated from a metal solution, as described in refs and . The intentional addition of carbon during the crystal growth perturbs the formation of large high-quality hBN crystals and increases the BN polycrystallinity while keeping the sp 2 -bonding (without any signature for a turbostratic phase in X-ray diffraction measurements, see the Supporting Information), and creates defects and emission lines in carbon-doped BN. , In order to perform advanced characterization measurements in such a polytypic BN sample, we have detached a submillimeter piece, shown in Figure , made of three crystals. We will demonstrate below that hexagonal/Bernal/hexagonal phases alternate from left to right, the bBN crystal sitting in the central part, with a triangular shape and a size of ∼50 μm 2 .…”