Synthesis and Characterization of Lightweight Beryllium Chloro Silicate Phosphor

Introduction

Various kinds of phosphors are already commonly used in many lighting devices, including common fluorescent tubes, electroluminescent wires, strips and surfaces, and LEDs. In a ubiquitous fluorescent tube, the inside is coated with phosphors of light weight .Electricity excites the gas-filled tube to produce shortwave light, which in turn causes the phosphors to become fluorescent and produce visible light. White LEDs, with their characteristics of compact size, high efficiency, long lifetime, low power requirement, light weight and energy savings (Zhu, 2012) can be widely used in various applications such as liquid crystal display backlighting, full-color displays, cell phones, and traffic signals. White LEDs are expected to replace conventional incandescent and fluorescent lamps in the near future (Du,2009). Eu2+-activated silicate phosphors, which have broad emission band through 5d–4f energy transition of Eu2+ activator ion, are suitable for the application of white LEDs. Eu2+ doped chlorosilicates give intense emission and which may be useful for many applications.

Silicate materials are useful in many applications of technological importance. Zeolites, a type of microporous aluminosilicates, are widely used as molecular sieves and catalysts. The zeolites have received less attention as potential luminescence materials. However, increasing interest in the study of guest-host composite materials has heightened research in these well-defined periodic microporous structures that are almost UV transparent and inexpensive. The lithium ceramics are promising breeder materials for fusion reactors. Rare-earth-containing silicate glasses have attracted great attention as potential materials for optical and magneto-optical devices such as an upconversion laser, a hole burning memory, and an optical switch. Though silicate-based phosphors are widely used as described in 1.6, there are some problems with synthesis and long-term use of silicates. Silicates need temperatures higher than 1000 C, even up to 1400 C for synthesis. They may get converted to glassy form. At high synthesis temperatures they can also react with low-cost crucible materials such as porcelain and china clay. During recent years, scientists have turned their attention towards chlorosilicates to get over these problems. In silicate lattices, an introduction of chloride ion can induce a red shift of excitation and emission bands of Eu2+ and Ce3+ ions because Cl ions with strong coordination effect can strengthen the crystal field splitting. Moreover, Chlorosilicates can be easily prepared by solid state reactions at temperatures below 1000 C, often as low as 700 C. They have good chemical, physical and thermal stability. Availability of cation sites with varying coordination and symmetries results in tunability of activator emission and excitation spectra. Variety of Chlorosilicates are known in chemistry and mineralogy.