The effect of annealing in various atmospheres (N2, H2, NH3 O2 and vacuum) on the 320 nm emission bands of hexagonal boron nitride (h‐BN) powders has been investigated by cathodoluminescence (CL). The CL intensity was decreased by annealing in the N2, H2and NH3 atmospheres at 1200 °C, with H2and NH3 having more effect than N2. On the other hand, the annealing in the O2 atmosphere increased the CL intensity remarkably at annealing temperatures higher than 800 °C. These results suggest that the oxygen located near the particle surface is related to the enhancement of the 320 nm bands in h‐BN. The highest CL intensity, which was obtained at an annealing temperature of 900 °C, reached to about one third of that measured for ZnS:Cu,Al phosphor under the same measurement conditions. The investigation of the powder annealed at higher temperatures in a vacuum indicated that the luminescent centers responsible for these emission bands are thermally stable up to about 1300 °C (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The synthesis of single crystal AlN particles has been carried out by the chemical vapor method using AlCl3 and NH3 as sources at 1450 °C. The x‐ray diffraction (XRD) measurement reveals that the samples are AlN in the wurtzite structure. The XRD line width had its minimum around partial pressure of NH3 (P (NH3)) of 0.25 atm, indicating the highest crystal quality among the samples synthesized in this study. The powders prepared at P (NH3) between 0.13 and 0.38 atm consisted mostly of particles with sizes ranging between approximately 100 and 500 nm. The particles in these samples had specific shapes with a sixfold symmetry reflecting the wurtzite crystal structure of AlN. The observation of particle morphology has also suggested that the particles composed of two crystal grains are included in the samples. The mechanism of particle formation was discussed based on the dependence of particle morphology on P (NH3). Comparison with the synthesis using vaporized Al as an Al source leads us to conclude that the use of AlCl3 is essential to the efficient formation of single crystal particles. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
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