Contents lists available at ScienceDirect Nuclear Inst. and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb Fading studies in LiMgPO 4 :Tb,B and synthesis of new LiMgPO 4 based phosphor with better fading characteristics S.N. Menon a,b , B.S. Dhabekar a, ⁎ , Sonal Kadam a , D.K. Koul a a Radiological Physics and Advisory Division, Bhabha Atomic Research Centre, Mumbai 400 085, India b Homi Bhabha National Institute, Anushaktinagar, Mumbai 400 094, India ARTICLE INFO Keywords: LiMgPO 4 :Tb,B LMP LMP-N OSL Linearity Dosimetry Fading ABSTRACT Lithium magnesium phosphate (LiMgPO 4 ) based phosphors have been found to be quite promising for optically stimulated luminescence (OSL) dosimetry. These phosphors have unique characteristic of linearity over a range of nine orders of magnitude of dose. However, the thermally stimulated luminescence (TL) and OSL signals of these phosphors fade with time. This constraint has limited the applicability of this phosphor in dosimetric application. This paper attempts to understand the cause and nature of fading. This paper also reports the synthesise of a new LiMgPO 4 based phosphor with less fading. 1. Introduction During the last two decades OSL has emerged as one of the most widely studied techniques in the field of radiation dosimetry like per- sonnel and environmental monitoring [1,2], space dosimetry [3], real- time in vivo dosimetry for radiotherapy beams, mammography and CT dosimetry [4]. The main advantages of OSL over TL are its efficiency, possibility of multiple readout, simpler instrumentation as no heating is involved and fast resetting of the dosimeter by bleaching within a few tens of seconds. Currently Al 2 O 3 :C is the most widely used OSL phos- phor in the world, though, BeO based OSL dosimetry is also being used in some countries [5]. Efforts are going on to develop OSL phosphors which can compete with Al 2 O 3 :C. In this direction LiMgPO 4 :Tb,B phosphor (LMP) was de- veloped and characterized by Dhabekar et al. [6]. It was found to be a highly sensitive phosphor with excellent dosimetric properties. The linearity of linearity over the range of nine orders of magnitude of dose range is unique to this phosphor. The only drawback was long term fading, which came in the way of its use in dosimetry. This phosphor was extensively studied by various researchers [7–11].Efforts were also made to synthesise this phosphor with different dopants [12,13]. Re- cently the development of LiMgPO 4 :Tb,B based dosimetry systems has also been reported [14]. Studies on the OSL properties of LMP by sev- eral authors point to the fact that this phosphor has a potential to be used as an OSL dosimeter if the fading aspect can be addressed. Re- cently, Malthez et al. [15] has employed various methods to reduce fading in LMP. The results of this study showed that the influence of fading can be minimized by applying preheat after irradiation or by IR bleaching before OSL readout. In this paper, we report the results of the fading studies carried out for a prolonged time period in LMP and plausible reasons for the fading of the signal. Efforts are also carried out to reduce the fading of the OSL signal by modifying the dopants in the material without compromising on the sensitivity and linearity of the phosphor. 2. Materials and methods LiMgPO 4 based phosphors were prepared by employing the solid- state reaction method [6]. To carry out TL/OSL studies, the phosphor was mixed with Polytetrafluoroethylene (PTFE) in the ratio of 1:3 and cold pressed to make circular discs (10 mm dia, 0.4 mm thick). PTFE was chosen as a binder material because it is not luminescent and its presence does not affect the TL and OSL results. To carry out fading studies, these discs were irradiated and then stored in dark for different time durations prior to the read out. All the discs stored for different time durations were read on the same day. TL and OSL measurements were carried out on automatic Riso TL/OSL reader model DA-20 having blue light-emitting diodes (λ = 470 ± 30 nm) as stimulation source. The stimulation power level was set at 90% of the maximum stimula- tion intensity (80 mW/cm 2 ). Hoya U-340 filter (I p ∼ 340 nm, FWHM ∼ 80 nm) was used during measurements. About 5 mg of phosphor in powder form was used to record the TL glow curve each https://doi.org/10.1016/j.nimb.2018.08.052 Received 22 June 2018; Received in revised form 31 August 2018; Accepted 31 August 2018 ⁎ Corresponding author. E-mail address: dbhushan@barc.gov.in (B.S. Dhabekar). Nuclear Inst, and Methods in Physics Research B 436 (2018) 45–50 0168-583X/ © 2018 Elsevier B.V. All rights reserved. T