Synthesis and Photo Luminescent Properties of Gd2O3 Based Rare Earth Nanophosphors

Abstract

In recent years, nanostructures, such as nanoplates, nanowires, nanotubes, and nanorods have attracted intensive attention due to their potential applications in a wide range of fields. Among these nanostructures, nanowires with small diameters and high aspect ratio are focused because of their novel physical properties and potential applications in catalysis and electronic, optical, optoelectronic, and magnetic devices. Therefore, much effort has been made toward the development of synthetic methodologies for fabricating inorganic nanowires, such as vapour-liquid-solid (VLS) growth processes, thermal evaporation, reverse micelles, hydrothermal routes and template confined methods. Among the various synthesis techniques, the hydrothermal method is a promising synthetic route, which can be better controlled through appropriate choice of reaction parameters, such as time, pH, and
temperature. It has some advantages, such as lower reaction temperature, energy economy, easily controllable reaction conditions, size-selective growth, controllable morphology, smaller particle size, and better particle size distribution. It has been proven to be an effective and convenient process in preparing high-quality anisotropic nanowires due to its great chemical flexibility and synthetic tenability. Since the rapid advances in nanotechnologies, particularly, the development of new methods for materials synthesis, there has been consistently growing interest in studying the optical behaviour of rare-earth (RE) ions in nanomaterials.Rare-earth compounds are very important in many areas, such as highquality phosphors, magnetic materials, and catalysts based on their novel
electronic, optical, and chemical properties because of their unique properties originating from the electron transitions within the 4f shells. RE-doped inorganic nanophosphor is one of the most promising materials for a variety of applications in solid-state lasers, lighting and displays, and bio-labels. The Gd2O3 microcrystal doped with Eu3+ ions are wellknown commercial red phosphors. Eu3+/Gd2O3 nanophosphors have also been used as fluorescent markers in a variety of immunosensing application. Since Gd3+ is a known contrast agent for magnetic resonance imaging (MRI), RE-doped Gd2O3 nanophosphors may function as both fluorescence and MRI labels. Despite the promising prospects of REdoped Gd2O3 nanophosphors, their optical behaviours, particularly, the excited state dynamics of RE ions deserve much more attention. A clear understanding of these aspects, however, is essential for the development
of novel bio-labels and nanosensors based on Er3+/ Gd2O3 nanophosphors with high luminescence efficiency. The luminescence decay in the nanocrystals shows non-exponential characteristics when excited directly  with temperatures varying from 10 to 300 K. This effect is attributed to energy transfer to defects in the nanocrystals. The calculated quantum efficiencies at various temperatures suggest that the change of lifetime with the temperature is predominantly influenced by the multi-phonon transition process to the next low-lying multiplet. Unusually strong phonon side bands with rich structures in the excitation spectra of Er3+ have been observed in Gd2O3 nanocrystals for hypersensitive transitions.