Temperature effects in 3.9 eV photoluminescence of hexagonal boron nitrideunder band-to-band and subband excitation within 7-1100 K range

Abstract The temperature dependence of the photoluminescence (PL) intensity of 3.90 eV in microcrystalline hexagonal boron nitride is studied in the range of 7-1100 K. The results obtained have been analyzed within the band model of energy levels of donor-acceptor pairs based on impurity (ON CN) complexes. Luminescence enhancement processes at T 220 K, when directly excited, the samples diminish the PL intensity because of the processes of thermal ionization of the donor level of the ON-center (122 meV) and the deep acceptor level of the CN-center (1420 meV) as parts of the (ON CN)-complex. In this case, the temperature enhancement region with an activation energy of 15 meV is due to the decay of a bound Wannier-Mott exciton followed by transfer of excitation to the associated donor-acceptor pair. With band-to-band excitation at T > 220 K, the temperature peculiarities of the PL under study are determined by non-radiative relaxation processes with activation energies of 57 and 252 meV, which are caused by shallow donor levels of VN- and ON-centers, respectively.