The present invention relates to compounds of formula I,

M.sup.IM.sup.II.sub.3 M.sup.III.sub.3M.sup.IV.sub.3N.sub.2O.sub.12:EuI

wherein, M.sup.I, M.sup.II, M.sup.III, and M.sup.IV have one of the meanings as given in claim 1, to a process of their preparation, the use of these compounds as conversion phosphors or in an emission-converting material, the use of these phosphors in electronic and electro optical devices, such as light emitting diodes (LEDs) and solar cells, and especially, to illumination units comprising at least one of these phosphors.

The present invention relates to a method of manufacturing a ceramic article (3) from a metal or metal matrix composite preform (1) provided by 3D-printing or by 3D-weaving. The preform (1) is placed in a heating chamber (2), and a predetermined time-temperature profile is applied in order to controllably react the preform (1) with a gas introduced into the heating chamber (2). The metal, the gas and the time-temperature profile are chosen so as to induce a metal-gas reaction resulting in at least a part of the preform (1) transforming into a ceramic. Preferred embodiments of the invention comprises a first oxidation stage involving a metal-gas reaction in order to form a supporting oxide layer (5) at the surface of the metal, followed by a second stage in which the heating chamber (2) is heated to a temperature above the melting point of the metal to increase the kinetics of the chemical reaction. The invention also relates to a number of advantageous uses of a ceramic article manufactured as described.

Provided are gallium nitride particles that have a low oxygen content and a high moldability and allow a gallium nitride sputtering target having a high density and a high strength to be produced. By causing a mixed powder of gallium oxide and gallium nitride to react at a temperature of 1000-1100 C. such that an ammonia reaction amount per hour is 1 or more times (by mole) an amount of gallium charged, gallium nitride particles are obtained of which an oxygen content is 1 atm % or less, an average particle size of primary particles is 5 m or more, and a particle size of a range of 10 area % from smallest particles of a particle size distribution (10% particle size) is 3 m or less.