Synthesis of single-phase nanocrystalline garnet phosphor derived from gel-network-coprecipitation

Abstract

Three compounds exist in the system Y2O3-Al2O3: Y4Al2O9, YAlO3, and Y3Al5O12 [1]. Y3Al5O12(YAG), and the most important of these compositions exists in the cubic form with a garnet structure. It is an important crystal for fluorescent and solid-state lasers, because it exhibits a thermally stable lattice, a well-determined crystal structure, and most importantly, resists saturation at high current excitation [2, 3]. Single crystals of Cr3+-doped YAG for example, are used in solid state lasers and Tb3+-doped YAG gives a characteristic narrow-band phosphor suitable for contrast-enhanced display applications [4, 5]. YAG phosphor powders are normally synthesized at relatively high temperatures by solid-state reaction between Y2O3 and Al2O3. Such conditions lead normally to powders of relatively large and varied grain sizes (5–20 μm) and varying impurity content. There are often problems in obtaining phase-pure material because of the intermediate formation of other phases, such as Y4Al2O9 and YAlO3 [6]. To achieve the desired phase purity and required particle size, high temperature treatment (>1600 ◦C) and extensive ball milling, which generally introduces additional impurities and defects and greatly reduces luminescence efficiency, are essential. For phosphor applications, it is desirable to have a fine particle size for high resolution and chemical purity for optimum chromaticity and brightness [7]. A few chemical synthesis techniques, such as sol-gel [8, 9], precipitation of hydroxides [10, 11], thermal decomposition of nitrates [12], hydrothermal treatment [13] and combus-