Synthesis of AlN: Eu2+ green phosphors by a simple direct nitridation method.

Eu-doped aluminum nitride phosphors were successfully prepared using simple direct nitridation of a metallic aluminum and Eu2 O3 powder mixture in flowing ammonia. AlN formed at reaction temperatures >900°C, and Eu3+ transformed into the secondary oxide phase EuAl2 O4 in the nitridation condition. Phase pure AlN was obtained by post-heat treatment of the nitridated product at 1600°C for 3 h in a nitrogen atmosphere, with an Eu2+ doping concentration < 0.5%. The phosphors exhibited broad green emission centered at 521 nm under 363 nm excitation. The luminescence of the phosphor was significantly influenced by the post-heat treatment temperature, which affected the dissolution of Eu2+ , phase purity, crystallinity, and particle size of the AlN host.

Direct Nitridation Synthesis of Quasi-Spherical ß-Si3N4 Powders with CaF2 Additive.

In this work, the quasi-spherical ß-Si3N4 powders were synthesized via an efficient direct nitridation strategy with CaF2 as the catalytic material under NH3 atmosphere. The effect of CaF2 on phase composition and crystalline morphology was studied. CaF2 additive can accelerate the nitridation of silicon powders, and the particles of nitridation products tend to have an equiaxed structure with the CaF2 additive increasing. When 4 wt% CaF2 additive or more was added, submicron ß-Si3N4 particles with quasi-spherical morphology and eminent crystal integrity were obtained. In contrast, irregular α-Si3N4 particles appear as the main phase with less than 4 wt% CaF2 additive. The growth mechanism of Si3N4 particles was also discussed. CaxSiyOz liquid phase is crucial in the nitridation of silicon powders with CaF2 additive.

Fabrication and Characterization of Short Silicon Nitride Fibers from Direct Nitridation of Ferrosilicon in N2 Atmosphere.

Short silicon nitride fibers were fabricated by direct nitridation of ferrosilicon in N2 atmosphere, and their structure and possible growth mechanism were characterized and investigated. The rod-like fibers which were α-Si3N4 with a low degree of crystallization and a high aspect ratio had a diameter of about 4 µm and a length close to a few millimeters. Belt-like fibers with a width about 5 µm and a thickness about 1 µm were also found in the nitrides. Scanning electron microscope (SEM), transmission electron microscope (TEM), high resolution transmission electron microscope (HRTEM), and selected area electron diffraction (SAED) investigations indicated that the fibers were single-crystalline α-Si3N4 with few amorphous distributed in the edge region, and the fibers grew by vapor⁻liquid⁻solid (VLS) mechanism.