Charge carrier trapping processes in un-doped and BaAl2O4:Eu3+ nanophosphor for thermoluminescent dosimeter applications

Abstract

The thermoluminescence (TL) mechanism for un-doped and europium (Eu3+) doped barium aluminate (BaAl2O4) were investigated and the location of energy levels for electrons/holes traps were determined in the aluminate for TL dosimetry applications. The solution combustion technique was used to synthesize the un-doped and Eu3+ doped BaAl2O4 nanopowders. X-ray diffraction showed a hexagonal crystal structure with the space group P63. The average crystallite size were found to be 50 nm and between 41 and 61 nm for un-doped and doped samples. Scanning electron microscopy showed irregular spherical and needle shapes for the un-doped and doped samples. The Kubelka–Munk function was used to calculate the optical bandgap values of 5.47 and 5.26 eV, for the un-doped and doped samples, from the diffuse reflectance spectra. The fitted x-ray photoelectron spectroscopy data demonstrated that Ba occupied two different sites, Ba1 and Ba2. Time-of-flight secondary ion mass spectroscopy in spectral mode showed the formation of the crystal lattice with the presence of the dopant. The photoluminescent and cathodoluminescent spectra were characterized by the 5D0-7FJ transitions (J = 1, 2, 3, 4) of Eu3+ with the dominate emission obtained at J = 2. A strong TL glow curve with peaks at 397 and 453 K were observed for the un-doped and doped nanopowders after irradiation with γ-rays. The doped nanopowders showed the highest TL intensity because doping with Eu3+ lead to the formation of additional trapped electrons and holes. The un-doped sample showed strong green (546 nm) TL emission due to the presence of a Vk3+ center. Whereas the Eu doped nanopowders exhibited strong TL emission at 615 nm.