Low-temperature synthesis of single-phase nanocrystalline YAG:Eu phosphor

Abstract

Crystalline yttrium aluminum garnet (Y3Al5O12, YAG) exists in the cubic form with a garnet structure [1, 2]. Host crystal with yttrium aluminum garnet (YAG) structure has the advantage of relatively stable lattice and large thermal conductivity, so YAG substituted with Eu, Ce, or Tb is known as a rather efficient phosphor material [3]. YAG phosphors doped with activators are mainly synthesized by solid-state reaction techniques [4, 5]. To achieve desired phase purity and required particle size, the process of solid-state reaction usually needs lengthy high temperature treatment (>1600 ◦C) and extensive ball milling, which generally introduces additional impurities and defects. Furthermore, high temperature processing does not yield sufficient fine particles required to achieve enhanced screen resolution in phosphor applications. A few wet-chemical methods [6–10] are also used to prepare YAG powders. However, due to the coexisting of two detrimental phases, YAP (YAlO3) and/or YAM (YAl4O9) as intermediate phases, hightemperature calcining is necessary to achieve desired phase purity. In this letter, we describe a novel preparation method for nanocrystalline YAG:Eu phosphor by nitrate-citrate sol-gel combustion process. The sample prepared in the present work is designed to have an overall composition (Y1−0.05Eu0.05)3Al5O12. Al(NO3)3 · 9H2O (analytical grade), Y(NO3)3 · 6H2O (99.99% pure), Eu2O3 (99.99% pure), and C6H8O7 · H2O (hydrated citric acid, analytical grade) were used as starting materials. Highpurity Eu2O3 was dissolved in HNO3 and then dissolved in deionized water with a stoichiometric amount of yttrium nitrate, aluminum nitrate and an appropriate dosage of citric acid. After the mixed solution was heated at 60 ◦C and continuously stirred using a magnetic agitator for several hours, the solution turned to yellowish sol. Then, heated at 80 ◦C and stirred constantly, the sol transformed into transparent sticky gel. The gel was rapidly heated to 180 ◦C and an auto combustion process took place companying with the evolution of brown fume. Finally, a yellowish product, fluffy precursor, was yielded. The precursor was then heattreated at varying temperatures from 600 ◦C to 1000 ◦C for two hours in a muffle furnace in air. The crystalline development of the product was identified by X-ray diffraction analysis (XRD, Model