Thermoluminescence of combustion synthesized yttrium oxide

Abstract

Pure yttrium oxide (Y₂O₃) was prepared by solution combustion technique using disodium ethylene diamine tetra acetic acid (EDTA-Na₂) as fuel at ~ 350 °C. Powder X-ray diffraction (PXRD) pattern of Y₂O₃ revealed cubic crystalline structure with crystallite size in the range of 18–23 nm. The scanning electron microscopy (SEM) indicated the foamy and fluffy nature of the sample. Fourier transformed infrared spectroscopy (FTIR) revealed four prominent absorption with peaks at 3395, 1433, 875 and 566 cm^− 1. From the optical absorption studies the energy gap of the synthesized sample was found to be 5.72 eV. Two well resolved thermoluminescence (TL) glows with peaks at 475 and 626 K were observed in γ-irradiated Y₂O₃. The glow curves were analyzed and the average activation energy was found to be 0.505 and 0.977 eV respectively.

Introduction

Different techniques are applied to prepare nanocrystals. They include solid state reaction [1], wet chemical methods such as chemical vapor deposition [2], combustion [3], [4], sol–gel [5], aerosol pyrolysis [6] etc. The solid state reaction method has several shortcomings such as prolonged reaction time, larger size grain growth and poor homogeneity. However, the salient features of wet chemical methods are that the starting materials can be mixed at molecular level and the temperature of formation of the final products is as low as that of conventional solid-state reactions techniques. Among wet chemical methods, ‘solution combustion synthesis’ has several advantages. It requires simple apparatus and the materials used are more economical [7], [8]. It requires low energy, short time and this technique may also be employed to produce homogeneous, high-purity, crystalline oxides. The nature of crystallinity, surface area and agglomeration of the synthesized products are primarily governed by flame temperature during combustion which itself dependents on the nature of the fuel and the fuel-to-oxidizer ratio [9]. It is known that, a good fuel should react non-violently without producing toxic gasses and act as a complexing agent for metal ions [10]. EDTA-Na₂ is one such compound which serves as a fuel during the combustion reaction and gets oxidized by nitrate ions and this is used as a new technology for material synthesis [11]. This EDTA has several remarkable advantages in comparison with other fuels and it has the greater ability to chelate metal cations and forming very stable and soluble complexes. In this technique, the starting materials are mixed at the molecular or the atomic level in a solution and it is easy to control the composition and a high degree of homogeneity is obtained. It is an exothermic reaction and occurs with the evolution of heat and light. When the mixture of fuel and oxidizer is ignited, combustion takes place at high temperature and leads to growth of materials with nano crystalline form. Metal nitrates and hydrazine based compounds are used as oxidizer and fuels respectively to synthesize metal oxides [12].

Oxide phosphors are found to be suitable for field emission display (FED), vacuum fluorescent display (VFD), plasma panel display (PDP) and electroluminescence (EL) devices. Luminescence efficiency is found to increase as the size of the phosphor particle is decreased and the preparation of phosphor powders becomes very important in technological application [13]. When thermoluminescent material is exposed to γ-radiation, it absorbs and stores energy in the form of defects. A part of the stored energy is released in the form of visible light when the two types of defect centers are recombined upon warming the material.

Metal oxide matrix is proved to be an excellent host material for lasing action. The Y₂O₃ possesses high refractory properties, a high melting point (~ 2450 °C) and a high thermal conductivity (33 Wm^− 1 K^− 1). It is a suitable material for photonic waveguide due to its high band gap (5.72 eV), with a very high refractive index (~ 2) and a wide transmission range (280–8000 nm) [14]. Numerous techniques are applied on the synthesis of rare earth doped nanocrystalline Y₂O₃ [15], [16], [17], [18].

In the present work, Y₂O₃ nanopowder was synthesized by solution combustion technique in which EDTA-Na₂ was used as the chelating-fuel. Further, the TL behavior of the γ-irradiated Y₂O₃ has been studied and the enhancement in TL intensity with γ-ray dose was found. In addition the material was found to be a potential candidate in TL dosimetry.