Thermoluminescence Properties of Novel La 2 O 3 Phosphor Obtained by Solution Combustion Synthesis
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Thermoluminescence Properties of Novel La2O3 Phosphor Obtained by Solution Combustion Synthesis V. R. Orante-Barrón1, C. Cruz-Vázquez1, R. Bernal2, G. Denis3, E. G. Yukihara3 1
Departamento de Investigación en Polímeros y Materiales, Universidad de Sonora, Apartado Postal 130, Hermosillo, Sonora 83000 México. 2
Departamento de Investigación en Física, Universidad de Sonora, Apartado Postal 5-088, Hermosillo, Sonora 83190 México. 3
Physics Department, Oklahoma State University, 145 Physical Sciences II, Stillwater, OK 74078 USA.
ABSTRACT Thermoluminescence (TL) of La2O3 is reported for the first time. Novel La2O3 phosphor was obtained by solution combustion synthesis (SCS) in which a redox combustion process between lanthanum nitrate and urea at 500 °C is accomplished. The powder samples obtained were annealed at 900 °C during 2 h in air. X-Ray Diffraction (XRD) results showed the hexagonal phase of La2O3 for annealed powder samples. The TL glow curve obtained after exposure to beta radiation of these samples, displayed two maxima located at ~ 101 °C and ~ 200 °C, and a shoulder at ~ 247 °C. Results from experiments such as dose response and fading showed that annealed La2O3 powder obtained by SCS is a promising material for radiation dosimetry applications. INTRODUCTION Lanthanum oxide (La2O3) is an insulator with a band-gap value of 4.3 eV. La2O3 has a hexagonal crystal structure with a P-3m1 space group [1]. In this structure each La ion is surrounded by seven oxygen ions: four in tetrahedral and three in octahedral coordination. This coordination is associated with the large radius of the lanthanum ion [2]. Although there are few reports on the photoluminescence properties of undoped and rare earth-doped La2O3 powder obtained only by hydrothermal synthetic methods [3-5], the stimulated luminescence properties such as thermoluminescence (TL) and optically stimulated luminescence (OSL) of undoped La2O3 synthesized by different methods (e.g. chemical co-precipitation, solution combustion synthesis, sol-gel) had not been studied yet. Furthermore, it is well known that structural and optical properties of semiconducting and insulating materials depend on the synthesis method and the type of annealing applied; it is convenient to use a method in which the synthesis parameters may be changed in order to achieve a kind of “tuning” on the stimulated luminescence properties of any studied phosphor. Solution combustion synthesis (SCS) is a technique in which a highly exothermic redox chemical reaction is carried out between a metal nitrate and a fuel (an organic amino-compound, mostly), resulting in nanocrystals with composition consistent with the initial reagents [6]. This
method represents simplicity, cost-effectiveness, high yield (mass content) and the capability to achieve high purity crystalline materials. In order to obtain high purity combustion products the oxidizing and the reducing reagents must be mixed in an aqueous solution in the proper molar ratio to achieve a stoichiometric coefficient (Φe) equal to
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