Silicate luminophor Zn 2 SiO 4 : Mn was synthesized using silica gel as an active form of silicon dioxide. Factors affecting the degree of crystallinity of the silicate obtained were studied. Willemite was doped with manganese(II) in the course of synthesis. The luminescence parameters of the resulting samples were estimated.The synthesis of luminophors for various applications and the improvement of their working parameters constitute one of the most topical problems of the technology of functional materials.Doped willemite Zn 2 SiO 4 : Mn is one of the first photo-, cathodo-, and X-ray-luminophors. It has been extensively studied with the aim to elucidate the fundamental physical aspects of luminescence and to study the effect of conditions of luminophor formation on the intensity and spectral parameters of luminescence.Although Zn 2 SiO 4 exists in three modifications, a-Zn 2 SiO 4 (rhombohedral structure of R3 space group) is usually formed under ordinary conditions. Luminophors based on zinc silicate are described in [135]. Willemite doped with manganese(II), which replaces Zn(II) in amounts of 0.535 wt %, emits light in the green spectral range. Industrial photoluminophors FL-530, FGI-520-1, FGI-528-1, and cathodoluminophors K-35, K-36, K-60, and KV-520-2 have been developed on its basis. To obtain a luminophor with orange-red luminescence, zinc silicate doped with Mn(II) should be formed in the presence of small amounts of beryllium and cadmium silicates, which are isomorphous to willemite [4]. Recently, willemite doped with rare-earth elements has been under investigation [6,7].Usually, doped willemite is synthesized by the solid-phase technique, by sintering a mixture of the appropriate oxides with silica at a temperature of about 1350oC for tens of hours [8]. It has been shown [4] that the degree of dispersion of the starting mixture strongly affects the reaction kinetics. This technique produces high-quality luminophors, being, however, rather power-consuming and sensitive to the difficultly controllable stock preparation process.The crystal perfection of a luminophor governs its luminescence characteristics [1]. In a nonequilibrium (deformed) matrix, many of luminescence centers are involved in nonradiative transitions, which diminishes the quantum efficiency and, accordingly, the intensity of luminescence. The concentration of an activator affects the efficiency both directly (via the number of centers) and indirectly (via the number of structural defects) [4,5].Apparently, it is necessary to develop such synthesis methods that would ensure a complete and controlled mixing of components (including dopants) in the preliminary stage and, consequently, an ordering of the forming structure under relatively mild conditions.The sol3gel technology finds increasing use for synthesis of luminophors. To synthesize doped willemite, oxides are transformed into nitrates. SiO 2 is obtained using a solution of tetraethoxysilane (TES) (C 2 H 5 O) 4 Si, which hydrolyzes under heating to give SiO 2 . Nitric acid and c...
Direct synthesis of MgSiN 2 from simple substances was performed in a flow-through system. The sequence of transformations that occur on heating mixed magnesium and silicon powders in flow of nitrogen was determined by X-ray phase analysis.Owing to the increasing interest in semiconductor nitrides, works on synthesis and study of A 2 B 4 N 2 compounds (A 2 , Mg or Zn; B 4 , Si or Ge) have been resumed recently [13 4]. These compounds inherit the structure of a double prototype compound A 3 B 5 (wurtzite or a derivative orthorhombic structure) and, as established by approximate calculations and experiments, must have electronic and optical characteristics closely similar to those of double nitrides.Aluminum nitride can not only be used as a widebandgap semiconductor, but is also regarded now as one of the best materials for substrates of integrated circuits. It has a higher thermal conductivity than the traditionally used aluminum oxide, which makes it possible to raise substantially the degree of integration and speed of response of integrated circuits. Similar applications are possible for a direct analogue of aluminum nitride, MgSiN 2 .The best known methods for synthesis of MgSiN 2 in the form of a powder are based on sintering of mixtures of double nitrides or on nitration of magnesium silicide [4]. The necessity for a preliminary synthesis of double half-products makes process more complex and is a potential source of impurities. This is especially true for the insufficiently chemically stable magnesium nitride.This study was aimed to carry out a direct synthesis of MgSiN 2 from simple substances: Mg, Si, and N 2 . The second goal was to perform a gas-phase synthesis of MgSiN 2 , using volatile Si compounds as a source and relying upon the volatility of Mg.The direct synthesis was performed in a tubular porcelain reactor connected to a gas-distributing system in such a way that a rarefaction, a flow of N 2 or Ar, or a static atmosphere of N 2 could be obtained in it. We used containers made of sintered corundum and inserts for collection of sublimates. The heating was performed in a resistance furnace. The temperature was monitored and controlled using platinum to platinum3rhodium thermocouples. The flow rates of high-purity gases {nitrogen [GOST (State Standard) 9293374] and argon (GOST 101 157379)} was dosed and monitored using valve floating rotameters.The starting mixture was prepared by a thorough dry mixing of powders obtained by mechanical grinding of high-purity ingots of Mg (GOST 6001379) and Si (semiconductor-grade purity, GOST 19 658381). The particle size was 100 3200 mm for the magnesium powder and <10 mm for the silicon powder.The mass of the starting substances, reaction products, and, in some cases, sublimates was measured on an analytical balance. X-ray diffraction patterns were obtained with Fe K = radiation at angles 2q = 203120oC. The processing of the results relied upon the PDF-2 database [5].The Mg : Si ratio in the starting mixture was varied within the range 131.8 to compensate for t...
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