Synthesis of Magnesium Based Nanophosphors and Nanocomposites by Different Techniques: Silicates and Ferrites

Introduction

Nanomaterials find wide range of applications due to their unique chemical, physical, electrical, magnetic, optical and mechanical properties. Because of these properties, they were useful as catalyst, sensors, coating materials, tunable lasers, and memory devices. The unique spectroscopic properties of rare-earth ions in different host lattices was prompted the development of rare- earth luminescent materials for lamps, cathode ray tubes, radiation monitoring systems, lasers, scintillators, bio sensors and white light-emitting diodes (LEDs) Cho. et.al (2010), Wang.et.al (2009) and Prashantha et.al (2011). White light-emitting diodes (LEDs) were the potential materials for significantly improving lighting efficiency, resulting in reduction of the excitation energy and also reduction in pollution from fossil fuel power plants Li et.al (2011). In order to enhance the quality of white-light, one of the current academic interest is the research for phosphors of single-component and cost effective preparation methods. The demand for developing efficient luminescent materials such as rare earth activated powders were attracted researchers due to their possible photonic applications, good luminescent characteristics, stability in high vacuum, biosensors and absence of corrosive gas emission under electron bombardment when compared to currently used sulfide based phosphors. Among all the rare earth ions, Eu³⁺ was usually adapted as a red emitting center because of its unique 4f⁶ structure that can be activated by ultraviolet rays effectively and emit high purity color of the red light Zhang et.al (2010), Brito et.al(2012) and Maldiney et.al(2012). Near-ultraviolet (NUV) conversion was the most suitable method which can achieve WLED. In this method, red/green/blue tricolor phosphors were pumped by NUV to generate white light. So phosphors play a crucial role in these solid-state lighting devices. However, the luminescent efficiency was low in this system owing to the strong re-absorption of the blue light by the red and green phosphors Chen et.al(2010), Li et.al(2012) and Cho et.al(2010).

The silicates are the largest, the most interesting and the most complicated class of minerals. The richness in crystal structures endows silicates affluent chemistry, physics and materials content including Geolites, Mesoporous materials, inorganic-organic composites etc. Exploration upon new type nano structures of silicates with unexpected properties seems especially technologically and economically important, simply due to their low cost and richest resources Hao et.al(1998), Zhao et.al(1999). From ancient times minerals have been a convenient object for investigating the nature of luminescence. In the last decades, research have been carried out on almost exclusively on artificial analogs of the minerals CaF₂, ZnS, Ca₃ (PO₄)₂ .F, Zn₂SiO₄, Al₂O₃, and Mg₂SiO₄. The search of materials suitable for solid-state radiation dosimeters has been the aim of many researchers after the discovery of TL Nagabhushana(2002).

Forsterite is a member of the Olivine family of crystals. It has orthorhombic crystalline structure. Forsterite is a crystalline magnesium silicate which has extremely low electrical conductivity that makes it an ideal substrate material in electronics. On the other hand it shows good refractoriness, low thermal expansion, good chemical stability and excellent insulation properties even at high temperatures Saberi et.al (2006). Forsterite is known to be an insulator at high frequencies. In particular Cr³⁺ doped Mg₂SiO₄ found to be an excellent tunable laser material in the near IR range of 1.1-1.3 μm Tsai (2002). Forsterite is known to be a good Bioceramics material. Therefore it is significant to develop new type of bioceramics Ni et.al (2007).