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Hexagonal boron nitride (h-BN) films were grown on c-plane sapphire substrates by low-pressure chemical vapor deposition with BCl3 and NH3 as the boron and nitrogen sources, respectively, and the influences of growth parameters on the film quality were investigated for samples with a thickness of about 1 µm. The dependence of X-ray diffraction on the growth temperature (T g) indicated that the crystalline quality is most improved in the sample grown at 1200 °C, in which the epitaxial relationship of {100}h-BN ∥ {110}sapphire and {001}h-BN ∥ {001}sapphire was confirmed. This condition enhanced lateral growth, resulting in the formation of grains with flat top surfaces. The T g dependence was discussed in relation to the amorphous AlN formed on the substrate surface and the reaction between BCl3 and NH3 in the vapor phase. The correlation between the structural and luminescent properties, which was found from the T g dependence of CL, was also discussed.

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The radiative performance of hexagonal boron nitride (h-BN) was assessed by the spatio-time-resolved luminescence measurements on its microcrystals (MCs) annealed in an O2 gas ambient. The MCs exhibited distinct deep ultraviolet luminescence peaks higher than 5.7 eV, although h-BN is an indirect bandgap semiconductor. The result indicates a strong interaction between the indirect excitons (iXs) and LO/TO (and LA/TA) phonons at T points of the Brillouin zone. Such phonon replicas of free iXs and a luminescence band at 4.0 eV showed negligible thermal quenching, most probably assisted by the strong excitonic effect, enhanced phonon scattering, and formation of a surface BxOy layer that prevents excitons from surface recombination by the thermal excitation. Conversely, the luminescence band between 5.1 and 5.7 eV, which seems to consist of LO/TO phonon replicas of iXs localized at a certain structural singularity that are further scattered by multiple TO phonons at K points and another two emission peaks that originate from the singularity, showed the thermal quenching. In analogy with GaN and AlGaN, cation vacancy complexes most likely act as native nonradiative recombination centers (NRCs). In the present case, vacancy complexes that contain a boron vacancy (VB), such as divacancies with a nitrogen vacancy (VN), VBVN, are certain to act as NRCs. In this instance, iXs delocalized from the singularity are likely either captured by NRCs or the origin of the 4.0 eV-band; the latter is assigned to originate from a carbon on the N site or a complex between VB and an oxygen on the N site.

An AlN phosphor that was coactivated by Ce 3+ and Si 4+ ions was synthesized by gas pressure sintering (GPS) at 2050 °C for 4 h in a 0.92 MPa nitrogen atmosphere. The phosphor emits blue color with the Commission International de l'Eclairage (CIE) chromaticity coordinate of (0.15, 0.07), which is close to the National Television Standard Committee (NTSC) blue coordinate. The crystallization and cell parameters of the samples were investigated by Rietveld refinement and high-resolution transmission electron microscopy (HRTEM). Since the ionic size of Ce 3+ ions are much larger than that of Al 3+ ions, the locations of rare earth (RE) ions in the AlN lattice are unclear. An octahedral interstitial site inside the wurtzite structure is proposed to be the site for RE ions. The effect of Si substitution was verified by energy-dispersive X-ray spectroscopy (EDX) and solid-state nuclear magnetic resonance (ssNMR). Cathodoluminescence (CL) was examined under electron bombardment at different accelerating voltages. Nitride phosphor exhibited high brightness and favorable stability. This study reveals the superior characteristics of nitride compounds in field emission display (FED) applications.