O Legorreta-Alba, E Cruz-Zaragoza, D Díaz and J Marcazzó
Magnesium tetraborate; Dysprosium; Thermoluminescence; Beta-radiation; Dosimeter.
|PUBLISHED DATE||August 6, 2018|
|PUBLISHER||The Author(s) 2018. This article is published with open access at www.chitkara.edu.in/publications.|
The synthesis and thermoluminescent characteristics of dysprosium-doped MgB4O7 are analyzed. The phosphor at different concentrations (0, 0.1, 0.5, 1, 2 and 4 mol%) of the dopant was prepared by the solution-assisted method. The magnesium borate compound was confirmed by X-ray diffraction. The annealing and dopant concentrations effects on the crystalline matrix were investigated. The highest thermoluminescent sensitivity was found with 450°C of annealing temperature and at high Dy3+ concentration too. The un-doped MgB4O7 phosphor shows a broad glow curve which peaked at 199°C and about 306 °C. Introducing Dy3+ dopant in the matrix that behavior was strongly changed. The wide glow curve shows three glow peaks; two small shoulders at 124 and 195 °C, and a highest peak between 323 and 336 °C temperature range. A large linear dose-response (5 – 2000 mGy) beta dose was obtained. The complex glow curves were deconvolved and the kinetics parameters were determined considering the general order kinetics model.
Alkali earth ions such as Li, Zn, Sr, Ca, and Mg based on tetraborate compound have been considered as important luminescent materials because of their excellent thermal and chemical stability, simple synthesis and cheap reagent material [1-8]. In particular, the MgB4O7 phosphor is attractive due to its low effective atomic number (Zeff = 8.4) close to that of soft biological tissue (Zeff = 7.42) and less value than that of the compact bone (Zeff = 13.59), which implies a small photon energy dependence [9-10]. However, the undoped magnesium borate has a low thermoluminescent (TL) sensitivity. Due to this disadvantage, MgB4O7 has been doped with different trivalent ions mainly of rare earths such as Gd, Ce, Tm, Nd, Dy, Eu, Ho [11-16], since it is known that the addition of small amounts of activators with another charge number of valence [9, 17-18] may increase the concentration of imperfections that are important factors improving the TL property of the host matrix. Special attention has been given to the TL study of Dy3+ doped MgB4O7 [5,18]. From the first studies of this phosphor material, carried out by Hitomi et al. [7,19], considerable effort has been devoted to improves its TL properties. In different works [5, 10, 15, 20-21], it has been reported that MgB4O7: Dy3+ in addition being a material closely equivalent to the soft biological tissue presents a high sensitivity, a single thermoluminescent peak at about 200 °C, with linearity in the dose-response curve over a wide range of doses, good reproducibility and low fading of the TL signal. Currently, the works related to MgB4O7:Dy3+ focused on evaluating the optimal conditions of a highly sensitive materials , also have been leaning to the determination of the influence of their structural characteristics . In this sense, knowing that the TL characteristics of the magnesium borate material are determined by its preparation method [5, 17, 23–24], in this work the TL characteristics of MgB4O7:Dy3+ were obtained by the, scarcely known, solution-assisted method.
|ISSN||Print : 2321-8649, Online : 2321-9289|
Dysprosium doped MgB4O7 and un-doped crystalline phosphor were synthetized using the solution-assisted method. The formation of the crystalline matrix was determined by means of X-ray diffraction. The highest thermoluminescent sensitivity was obtained with annealing at 450°C. The TL intensity of magnesium tetraborate was improved with 4 mol% of Dy3+ dopant. The introduction of Dy3+ with varying concentrations in the matrix strong activates the TL phenomenon and changed the structure of the glow curves of the MgB4O7 . It seems that the experimental TL glow curves was forming by three overlapped peaks at about 124, 195 and about 336 °C. The complex glow curves were acceptable deconvolved by four peaks, with FOM less than 1.2%, indicating that the general order kinetics model was appropriate to well described the thermoluminescence of this phosphor. MgB4O7 :Dy3+ compound presents an interesting and useful linear dose-response for measuring low β-radiation doses, which can be useful in radiation therapy doses.