Particle size effect on TL/OSL response of NaMgF3:Tb phosphor

Abstract

NaMgF3 is a nearly tissue equivalent material with low Zeff = 10.4 and a well-known phosphor for its high sensitivity concerning luminescence. The type of preparation route followed greatly affects the luminescence efficiency of a material. Grinding of NaMgF3:Tb phosphor for a long time induces several lattice defects in the phosphor. In this work, effect of particle size on TL/OSL response of NaMgF3:Tb irradiated by 60Co source of gamma radiations with a dose of 15 Gy has been investigated. NaMgF3:Tb samples has been synthesized by solid state reaction method using different grinding times i.e. 1 h and 5 h. XRD technique confirms its formation and crystallite size is calculated. TL studies show that sample synthesized by 5 h grinding is almost 2 times more intense than the sample obtained by 1 h grinding. Also, a clear enhancement is seen in the shoulder peak of sample grinded for 5 h. This could be due to increase in occupancy of trapped charge carriers in the trap levels. However, the position of main TL glow peak remains same in both the samples. Associated TL kinetic parameters such as order of kinetics, activation energy, frequency factor and trap density have been calculated by deconvoluting the TL glow peaks to understand the TL phenomenon. Continuous-wave optically stimulated luminescence (CW-OSL) decay curves have been obtained under blue LED stimulation for 40 s. Analyzing the CW-OSL decay curves reveal that grinding time significantly affects the OSL intensity of the phosphor as well. The decay constant and photoionization cross-section is determined for the faster and slower components of the total OSL intensity. It could be concluded that the time of grinding taken during preparation of the material has a major role in affecting the concentration of trap levels formed inside the forbidden gap of the phosphor.