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ARTICLE
Year : 2011  |  Volume : 34  |  Issue : 1  |  Page : 32-33  

Thermoluminescence studies of copper and indium doped Li 2 B 4 O 7 single crystals


1 Radiation Safety and Systems Division, BARC, Mumbai, India
2 Technical Physics Division, BARC, Mumbai, India

Date of Web Publication17-Mar-2012

Correspondence Address:
M S Kulkarni
Radiation Safety and Systems Division, BARC, Mumbai
India
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Source of Support: None, Conflict of Interest: None


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  Abstract 

Highly transparent single crystals of Li 2 B 4 O 7 i.e. lithium tetraborate (LTB) doped with Cu (0.25 wt. %) and Cu & In (0.5 wt. % each) were grown by the Czochralski method. The Li 2 B 4 O 7 : Cu and Li 2 B 4 O 7 :Cu, In crystals were studied using thermoluminescence (TL) technique. The TL readout of Li 2 B 4 O 7 :Cu crystals showed two well-defined glow peaks at 130 o C and 235 o C for heating rate of 4K/s, whereas in LTB:Cu, In another shoulder peak on low temperature side of the main peak is seen. The TL sensitivities of LTB:Cu and LTB:Cu, In were found to be 3.3 and 6 times to that of TLD-100 respectively. Both the LTB:Cu and LTB:Cu, In crystals exhibit a linear TL dose response in the dose range from 1 mGy to 1 kGy. The single crystal of Li 2 B 4 O 7 : Cu,In could become a potential TL phosphor for medical and clinical dosimetry owing to its very good sensitivity and excellent tissue equivalence.

Keywords: Thermoluminescence, crystal growth, trap depth, initial rise method


How to cite this article:
Rawat N S, Kulkarni M S, Desai D G, Tiwari B, Ratna P, Gadkari S C. Thermoluminescence studies of copper and indium doped Li 2 B 4 O 7 single crystals. Radiat Prot Environ 2011;34:32-3

How to cite this URL:
Rawat N S, Kulkarni M S, Desai D G, Tiwari B, Ratna P, Gadkari S C. Thermoluminescence studies of copper and indium doped Li 2 B 4 O 7 single crystals. Radiat Prot Environ [serial online] 2011 [cited 2019 Dec 10];34:32-3. Available from: http://www.rpe.org.in/text.asp?2011/34/1/32/93937


  1. Introduction Top


Lithium tetraborate (LTB) is one of the potential materials studied for applications in the thermoluminescence (TL) dosimetry. The near tissue equivalence (effective atomic number, i.e. Z eff =7.4) and energy independent response of LTB has attracted several investigations aimed towards improvement in its sensitivity which involved the use of various dopants like Mn, Cu, Ag, In and others. Doped LTB is found to have increased TL sensitivity. Lithium borate doped with Mn was the first material reported for TL dosimetry (Schulman, et al., 1967). Amongst many dopants that were tried with LTB, Cu has been found to be the most successful. Single crystals of LTB doped with Cu; Cu,In and Cu,Ag are found to have higher TL sensitivity among the doped LTB crystals (Burak et al., 2002). In addition, LTB can also be made suitable for neutron dosimetry applications by increasing the concentration of 10 B and 6 Li in Li 2 B 4 O 7 .

Copper is one of the common activators used in inorganic phosphor systems and is found to be an efficient luminescence center in numerous phosphor materials. Copper doped LTB as a TL phosphor was suggested for radiation dosimetry by Takenaga et al (1980). It is reported that Cu-doped LTB has the most intense emission for UV excitation (Senguttuvan et al., 2002). Sintered LTB doped with Cu; Ag, In; and Cu, In have been reported to show better dosimetric characteristics (Prokic, 2001). TL sensitivities of these two phosphors are reported to be 2 and 0.7 times, respectively than that of TLD-100.

LTB single crystals can be grown by using Czochralski and Bridgman methods. In the present study Li 2 B 4 O 7 single crystals doped with i) 0.5 wt% Cu and ii) 0.5 wt% of Cu, In together were grown by the Czochralski method. The as-grown crystals were characterized by TL technique.


  2. Experimental Top


Single crystals of Li 2 B 4 O 7 : Cu and Li 2 B 4 O 7 :Cu,In were grown by the Czochralski method. An automatic diameter controlled crystal puller (Oxypuller, Cyberstar) was used for the crystal growth. Commercially available Li 2 B 4 O 7 polycrystalline powder material (99.99+ % pure, Aldrich make) was used as a starting charge for the growth. For growing LTB:Cu crystal, high purity CuO (0.5 wt.%) was mixed in the starting Li 2 B 4 O 7 polycrystalline charge and for growing LTB:Cu,In high purity CuO (0.25 wt.%) and InO (0.25 wt.%) were mixed in the starting Li 2 B 4 O 7 polycrystalline charge. The temperature of the charge contained in a platinum crucible of 40 mm diameter was raised to a few degrees above its melting point (917°C) to commence the growth. The application of a pull rate of 0.2 mm/h, a rotation rate of 10 rpm and a high longitudinal thermal gradient of about 70°C/cm, enabled the growth of clear core free transparent crystals, 20 mm in diameter and of various lengths. The crystals grown at higher rates showed fogginess. The disc of size 20 mm diameter and 2 mm thickness were cut out from the grown crystal and optically polished on either side. From this, crystals of the size 3 mm x 3 mm were cut out for TL studies.


  3. Results and Discussion Top


Single crystals of LTB: Cu and LTB: Cu,In were given annealing treatment at 350°C for 15 minutes. The TL measurements were carried out at 3.5 K/s using the programmable TL reader system (Ratna et al., 2006). The TL glow curves for LTB:Cu and LTB:Cu,In are given in [Figure 1]. LTB: Cu, In is found to have sensitivity 1.8 times to that of LTB:Cu. Thus co-doping of Indium along with copper has resulted in increased sensitivity. The TL glow peaks in LTB:Cu,In single crystal were observed at 135, 182 and 235°C and that for LTB:Cu at 130 and 235°C. The phosphor shows excellent linear dose-response in TL domain as shown in [Figure 2].
Figure 1: TL curve for LTB: Cu and LTB: Cu, In for an absorbed dose of 1Gy (from 90Sr/90Y beta source) at a heating rate of 3.5K/s

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Figure 2: TL dose response of LTB: Cu, In

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The trap depths of two TL peaks for LTB:Cu are estimated to be 0.8 eV and 1.72 eV using initial rise method. The trap depths for 135 and 235°C peaks for LTB:Cu,In are found to be similar and is attributed to the presence of copper ion in the host material. The low temperature peak in both LTB:Cu and LTB: Cu,In is found to fade completely within 24 hours. The high temperature TL peak in LTB:Cu and LTB:Cu,In is found to be very stable and has negligible fading when stored at room temperature for a period of one month.


  4. Conclusions Top


The doping of Cu (0.25 wt.%) and Indium (0.25 wt.%) in LTB is found to enhance the TL sensitivity of LTB:Cu,In by a factor of 1.8 as compared to LTB:Cu. The TL glow curve for LTB:Cu,In single crystals has TL peaks at 135, 182 and 235°C and that for LTB: Cu is at 130 and 235°C. The trap depths of two TL peaks for LTB: Cu is estimated to be 0.8 eV and 1.72 eV using initial rise method. The trap depths for 135 and 235°C TL peak in LTB:Cu, In are found to be similar to the corresponding peaks for LTB: Cu and is attributed to the presence of copper ions in the single crystals of LTB. The material has potential application in field of personnel monitoring and medical physics as it is a very good tissue equivalent material. The optimum concentration of dopants like Copper and Indium in LTB single crystals needs to be investigated and is a topic of future studies.


  5. References Top


  1. Burak Ya. V., Padlyak B.V. and Shevel V.M. (2002), Rad. Eff. Defects in Solids, 157, 1101.
  2. Prokic M. (2001), Radiat. Meas. 33, 393-396.
  3. Ratna P., Chaudhury P. Nilshree G. and Sharma D.N. (2006), J. Med. Phys., 31, 200.
  4. Schulman J.H., Kirk R.D. and West E.J. (1967), Luminescence dosimetry, U.S. At. Energy Comm. Symp. Ser. 8, Conf-650637, 113.
  5. Senguttuvan N., Ishii M., Shimoyama M. (2002), Nucl. Instrum. Meth., A 486, 264.
  6. Takenaga M., Yamamato O. and Yamashita T. (1980), Nucl. Instrum. Meth., 175, 77-78.



    Figures

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  In this article
Abstract
1. Introduction
2. Experimental
3. Results and D...
4. Conclusions
5. References
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