Near band-gap photoluminescence properties of hexagonal boron nitride

Abstract

Near band-gap luminescence (hν≥5 eV) of hexagonal boron nitride has been studied by means of the time-and energy-resolved photoluminescence spectroscopy method. Two emissions have been observed at 5.5 eV and 5.3 eV. The high-energy emission at 5.5 eV is composed of fixed sub-bands assigned to bound excitons at 5.47 eV, 5.56 eV and 5.61 eV. The non-structured low-energy emission at 5.3 eV undergoes a large blue shift (up to 120 meV) with a linear slope exc lum E E ∆ ∆ / <1 with increasing excitation energy E exc . At 7 . 5 ≥ exc E eV, the band position is fixed and marks the transition from the Raman to the photoluminescence regime. We assign the 5.3 eV band to quasi donor-acceptor pair (q-DAP) states due to electrostatic band fluctuations induced by charged defects. The shift is explained by photo-induced neutralization of charged defect states. The absence of contribution to the q-DAP luminescence from exciton suggests the existence of a large exciton binding energy, which is qualitatively consistent with theoretical predictions. 3

Photoluminescence properties of pyrolytic boron nitride

“…Three luminescence bands are observed at energies of 5.3 eV, 3.75 eV and 3.1 eV. The very weak band at 5.3 eV has been previously reported in hBN microcrystal and assigned to quasi-donor-acceptor pair (qDAP) radiative transitions [6]. The most intense band at 3.75 eV (330 nm) is broad ( eV 0.6 ∆E ) and has a rather symmetric shape.…”

“…Luminescence properties of high purity commercially available hBN microcrystal powders have been largely studied in cathodoluminescence [2][3][4][5] and photoluminescence [6][7][8][9][10][11][12][13][14] experiments. Due to the synthesis methods used, these powders are inherently contaminated by carbon, calcium and oxygen impurities.…”

“…Luminescence spectra of usual hBN microcrystal powder are displayed on Figure 4 These spectra have been obtained in the same experimental conditions that pBN luminescence spectra and are discussed in details in recent papers [6,13]. A comparison between luminescence properties of both kinds of samples brings information.…”

Point defects in hexagonal BN, BC3 and BCxN compounds studied by x-ray absorption near-edge structure

“…Since then, several photo-and cathodoluminescence studies [3][4][5]7,8,[32][33][34] have been published in an effort to understand the electronic and optical properties of h-BN. According to these reports, exciton formation, impurities and defects are responsible for h-BN luminescence, due to the formation of acceptor and donor levels in the bandgap.…”

Picosecond laser structuration under high pressures: Observation of boron nitride nanorods

“…Fluorescence and fluorescence excitation spectra in the UV-VUV spectral region of fresh and irradiated hBN samples were measured at the Superlumi experimental station of Hasylab of synchrotron DESY [12][13]. During these measurements the samples were maintained at low temperature of 9 K under high vacuum of ~10 -9 mbar.…”