Photoluminescence and thermoluminescence ...

2 downloads 0 Views 3MB Size Report
Jul 27, 2015 - In addition, it is desirable for the dosimetric material used in personal dosimetry ... num crucible (containing the mixture) inside an electronic.
Research article Received: 26 May 2015,

Revised: 27 July 2015,

Accepted: 27 July 2015

Published online in Wiley Online Library

(wileyonlinelibrary.com) DOI 10.1002/bio.3020

Photoluminescence and thermoluminescence properties of Li2O-Na2O-B2O3 glass N. A. Razak,a S. Hashim,a M. H. A. Mhareba,b* and N. Tamchekc ABSTRACT: Influence of Nd3+ concentration on the optical and thermoluminescence (TL) properties of melt-annealed synthesized 10 Na2O: 20 Li2O: (70-x) B2O3: xNd2O3, where 0.1≤ x ≤0.7 (LNB) glasses are determined. The absence of sharp peaks in X-ray diffraction patterns confirms the amorphous nature of the prepared glasses. The photoluminescence spectra under 800 nm laser excitations at room temperature exhibit three prominent peaks centred at 538, 603 and 675 nm corresponding to the transitions of 4G7/2 → 4I9/2, [4G7/2 → 4I11/2, 4G5/2 → 4I9/2] and [4G7/2→ 4I13/2, 4G5/2 → 4I11/2], respectively. The TL glow curve exhibits a prominent peak (Tm) at 180°C. The best performance of the prepared glass was found at 0.5 mol% of Nd2O3. We achieved a good linearity of TL response against dose between 0.5 to 4.0 Gy. The calculated value of the effective atomic number, Zeff, is 7.55 which is nearly tissue equivalent (Zeff = 7.42). These promising features demonstrate the capability of the aforementioned glass to be used as a radiation dosimeter. Copyright © 2015 John Wiley & Sons, Ltd. HIGHLIGHTS The thermoluminescence and optical properties of new compositions of lithium sodium borate glasses doped with Nd3+ ions were reported. Attractive features were obtained from the TL, PL and UV–Vis light analysis. Three upconversion luminescences permitting green, orange and red emissions were observed. Keywords: thermoluminescence; photoluminescence; borate glass; neodymium oxide

Introduction The growing application of ultraviolet, X-ray and gamma radiations in various process associated with industrial, medical and agriculture fields has led to many on-going research studies in the search for new compositions with desirable dosimetric properties (1,2). Thermoluminescence (TL) is one of the techniques used in radiation dosimetry (3). The TL phenomenon works on the basis of forming a visual indication in which the energy stored in an irradiated material, when heated, will be released in the form of light emission. The intensity of the emitted light as a function of temperature will then form a glow curve. The position, shape and intensity of the glow peaks are related to the properties of the trapping states responsible for TL. The requirements in achieving a dosimeter of high precision include good linearity, chemical and thermal stability and low hygroscopicity (4). In addition, it is desirable for the dosimetric material used in personal dosimetry to be tissue equivalent. A dosimetric material that has a similar atomic composition to that of human tissue (Zeff = 7.42) will contribute to the more accurate determination of absorbed dose in soft biological tissue exposed to ionizing radiation (5,6). The best advantages of borate glass have become prominent in the TL field due to their properties of near-tissue equivalent, good rare earth (RE) ion solubility and are an easily handled process. However, the hygroscopic nature and relative stability of borate glass adversely affect its performance (7,8). Over several years these drawbacks have been overcome by incorporating suitable modifiers into the glass network. Lithium oxide is one of the most frequent modifiers used to improve borate stability.

Luminescence 2015

The incorporation of lithium ions into the glass system leads to the creation of vacancy by increasing the dislocation and improving the strength of the host (9). Furthermore, lithium borate also appears to be one of the most attractive materials in personal dosimetry due to its effective atomic number of 7.3 (10). Changes in TL features can be observed due to the presence of RE impurities in the host (11). Variation of the dopant sites with different ion–host interactions resulted in differences in spectral properties due to the incorporation of RE in glass. It could also form large complex defects and long range interactions which involve charge trapping and recombination components of the TL process, which ultimately enhance the TL response (12). Neodymium oxide (Nd2O3) is one of the REs used as a dopant in the

* Correspondence to: M. A. Mhareb, Department of Physics, Universiti Teknologi Malaysia, 81310 Skudai, Johor, Malaysia. E-mail: [email protected] a

Department of Physics, Universiti Teknologi Malaysia, 81310, Skudai, Johor, Malaysia

b

Radiation Protection Directorate, Energy and Minerals Regulatory Commission, 11183, Amman, Jordan

c

Department of Physics, Faculty of Science, Universiti Putra Malaysia, 43400, UPM Serdang, Selangor, Malaysia Abbreviations: FRGS, Fundamental Research Grant Scheme; MDD, minimum detectable dose; PL, photoluminescence; TL, thermoluminescence; XRD, X-ray diffraction.

Copyright © 2015 John Wiley & Sons, Ltd.

N. A. Razak et al. glass network due to its potential to enhance TL and create new defects (13). Products from the incorporation of Nd2O3 with materials such as CaS, CaF, Mal2O4, silicate laser glass and TeO2 glass are used as dosimeters for monitoring exposure to ionizing radiation such as UV light, X-rays and γ-rays (13). In this study, we investigate the optical and thermoluminescence properties of LNB glass doped with Nd2O3 for radiation dosimetry purposes. The prepared glasses are characterized using X-ray diffraction (XRD), PL and TL measurements.

Experimental Glass preparation Glasses of the form 10 Na2O:20 Li2O:(70-x) B2O3:xNd2O3 with 0.1≤ x ≤0.7 were prepared using a conventional melt annealing technique. Analytical grade high purity (Aldrich Company) powders of Li2O (99.9%), Na2O (99.9%), B2O3 (99%), and Nd2O3 (99.9%) were chosen as raw materials. Boron oxide was the glass former while lithium and sodium oxides were used as glass modifiers. Glasses were prepared by mixing a standard amount of lithium oxide (Li2O), sodium oxide (Na2O) and boron oxide (B2O3), followed by the addition of neodymium oxide (Nd2O3) as an activator. The constituents were thoroughly mixed for 30 min to obtain a homogenous mixture before placing the aluminum crucible (containing the mixture) inside an electronic furnace at 1300°C for 1 h. The molten mixture was frequently stirred to achieve complete homogeneity before being poured onto a steel plate and annealed at 400°C for 3 h to remove the remaining stress. Upon completing the annealing process, the furnace was switched off and gradually cooled down to room temperature using an average cooling rate of 10°C min1. Prepared glasses were stored in vacuum desiccators to prevent attack by moisture or other contaminants. The compositions of the prepared glasses with their codes are listed in Table 1.

Figure 1. XRD patterns of Li2O-Na2O-B2O3 glasses doped with different concentrations of Nd2O3.

after the irradiation to allow spurious signals to fade. For each experimental data point, five replicate samples were irradiated and measured to determine the average response and the standard deviation. Measurements of glow curves of the sample were performed with a Harshaw Thermoluminescence Dosimeter (TLD) reader Model 4500.

Results and discussion X-ray diffraction The XRD patterns are shown in Fig. 1, the presence of a broad ‘hump’ confirms the amorphous nature of the prepared glasses. Emission spectra

Glass characterization The amorphous nature of the glasses was examined via a Rigaku AX-2500 Advance X-ray diffractometer which uses Cu-Kα radiation (λ = 1.54 Å) at 40 kV and 30 mA with 2θ ranges from 10° to 80°. The emission measurement was performed using a Perkin Elmer LS-55 photoluminescence (PL) spectrometer (UK), in which a xenon discharge lamp in the wavelength range 510–720 nm is used as the excitation source. The glass samples also were irradiated with gamma radiation using a Cobalt-60 source. The irradiated samples were kept in a dark room under ambient temperature (25–30°C) to avoid any influence of background light. The curves were recorded 24 h

Figure 2 shows the upconversion emission spectra under 800 nm laser excitations. Three emission bands are observed at 538, 603

Table 1. The composition of prepared glass samples with their codes Glass codes

Li2O mol%

Na2O mol%

B2O3 mol%

Nd2O3 mol%

Nd0.1 Nd0.3 Nd0.5 Nd0.7

20 20 20 20

10 10 10 10

69.9 69.7 69.5 69.3

0.1 0.3 0.5 0.7

wileyonlinelibrary.com/journal/luminescence

Figure 2. Emission spectra of Li2O-Na2O-B2O3 glasses doped with different concentrations of Nd2O3.

Copyright © 2015 John Wiley & Sons, Ltd.

Luminescence 2015

Photoluminescence and thermoluminescence properties and 675 nm corresponding to the transitions 4G7/2→4I9/2, [4G7/ 4 4 4 4 4 4 4 2→ I11/2, G5/2→ I9/2] and [ G7/2→ I13/2, and G5/2→ I11/2], permitting green, orange and re-emissions, respectively. The emission transitions are comparable with that of other reported glasses (14–16). Balda et al. investigated upconversion of lead germinate glass under 806 nm wavelength excitation, exhibiting three emission bands at 535, 599 and 668 nm wavelengths which corresponded to 4G7/2→4I9/2, 4G7/2→4I11/2 and 4G7/2→4I13/2, respectively (14). Meanwhile, Silva et al. reported the upconversion of Nd3+ with PbO-GeO2 glass under excitation at 805 nm wavelength, with three emission bands localized at 535, 600, 670 nm wavelengths that correspond to transitions of 4G7/2→4I9/2, [4G7/2→4I11/2, 4G5/2→4I9/2] and (4G7/2→4I13/2, 4G5/2→4I11/2), respectively (15). Recently, research conducted by Mhareb et al. displayed three peaks of room temperature upconversion emission spectra at 540, 610 and 660 nm wavelengths correspond to (4G7/2→4I9/2), [4G7/2→4I11/2, 4G5/2→4I9/2] and [4G7/2→4I13/2, 4 G5/2→4I11/2] transitions, respectively, upon 800 nm wavelength excitations (16). Samples with 0.5 mol% of Nd2O3 content exhibit maximum peak intensity and intensity quenching is observed beyond this concentration. The quenching phenomenon explains that, at a certain limiting concentration, RE ions are spaced close enough to allow energy exchange between neighbouring ions to occur until the excitation ion reaches to a less excited state. The transition from this less excited state to the ground state is non-radiative and causes the luminescence to quench completely (17). Thermoluminescence characterizations Glow curve analysis. Figure 3 shows the glow curve of TL intensity versus temperature for different concentrations of Nd3+ ions. The prepared glasses were exposed to a test dose of 3 Gy by subjection to Cobalt-60 irradiation. For all the neodymium concentrations, the glow curves display a single prominent peak at a maximum temperature (Tm) of 180°C. The increase in the TL yield with Nd2O3 is clearly evidenced until the material reaches 0.5 mol% Nd3+ concentration. Beyond this concentration, a gradual decrease in TL intensity is observed due to concentration quenching phenomena. Therefore, the optimum TL response is determined to be 0.5 mol% Nd3+

Figure 3. TL glow curve of Li2O-Na2O-B2O3 glasses doped with different concentrations of Nd2O3 at a constant dose of 3 Gy.

Luminescence 2015

Figure 4. TL glow curve of Li2O-Na2O-B2O3 glasses doped with 0.5 mol% Nd2O3 at different heating rates.

concentration. In order to get an ideal dosimeter, the desirable prominent peak should be around 200°C. At low temperatures (