Synthesis of willemite by modified sol-gel technique

Abstract

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...

Optical properties of annealed Mn2+-doped ZnS nanoparticles

“…Usually, doped willemite is synthesized by the solid-phase technique i.e. by sintering a mixture of the appropriate oxides with silica at a temperature of about 1300-1350 1C for around 10 h [45]. This process is very energy consuming compared to our method that allowed the synthesis in 1 h at 800-1000 1C.…”

Synthesis and Structural Determination of the Disordered Bixbyite Cu3‐xSb1+xO5.5+3x/2 with Spin‐Glass Behaviour

“…Cu 9 Sb 4 O 19 hasb een referred to in severald ifferent studies but no further investigation has been done following from Shimada's work on this complex oxide even thoughn os tructural solution has been produced. [11][12][13][14] The solid-solution Cu 2 + x Ti 2-x Fe 2-x Sb x O 9 having ab ixbyite-type structure was homogenous over the range of x = 0t o1 .4, requiringa no xygen atmosphere to synthesise the copper/antimony rich end of the solution.Bye xtrapolation, the end of the solution was calculated to be Cu 4 Sb 2 O 9 with a ' 9.62 .M ouron et al identified that this could be the same oxide identified as Cu 9 Sb 4 O 19 by Shimada et al and believed that the structure of the oxide was likely closely related to the bixbyite type. [12] Bazuev rationalized this solid-solution by suggesting the notion of ad ouble substitution of cations, from Ti 4 + + Fe 3 + for Cu 2 + + Sb 5 + .…”

Síntese e estudo de ortossilicatos de zinco luminescentes com aplicação da técnica sol-gel

“…12 O método de síntese mais amplamente utilizado na obtenção destes materiais é a reação no estado sólido, o qual exige grande quantidade de energia e tempo. 10 A utilização da técnica sol-gel em substituição às reações de estado sólido começou a ser avaliada nos últimos anos, [13][14][15] apresentando inúmeras vantagens: alta cristalinidade, partículas de pequeno tamanho, homogeneidade da matriz e agentes ativadores, alta e eficiente luminosidade e ausência de fases não luminosas. 13 Estas particularidades do método serão discutidas neste trabalho.…”

“…10 A utilização da técnica sol-gel em substituição às reações de estado sólido começou a ser avaliada nos últimos anos, [13][14][15] apresentando inúmeras vantagens: alta cristalinidade, partículas de pequeno tamanho, homogeneidade da matriz e agentes ativadores, alta e eficiente luminosidade e ausência de fases não luminosas.…”