Ion size effects on thermoluminescence of terbium and europium doped magnesium orthosilicate
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Weigong Zhou School of Great Wall, China University of Geosciences, Beijing 100083, China
Adrian A. Finch Department of Earth & Environmental Sciences, University of St Andrews, Fife KY16 9AL, United Kingdom
Peter D. Townsend Physics Building, University of Sussex, Brighton BN1 9QH, United Kingdom
Yafang Wanga) School of Science, China University of Geosciences, Beijing 100083, China (Received 14 July 2015; accepted 2 October 2015)
Thermoluminescence (TL) and radioluminescence (RL) are reported over the temperature range 25–673 K from MgSiO4:Tb and MgSiO4:Eu. The dominant signals arise from the transitions within the Rare Earth (RE) dopants, with limited intensity from intrinsic or host defect sites. The Tb and Eu ions distort the lattice and alter the stability of the TL sites and the peak TL temperature scales with the Tb and Eu ion size. The larger Eu ions stabilize the trapped charges more than for the Tb, and so the Eu TL peak temperatures are ;20% higher. There are further size effects linked to the TL driven by the volume of the upper state orbitals of the rare earth transitions. For Eu the temperatures of the TL peaks are wavelength dependent since higher excited states couple to distant traps via more extensive orbits. The same pattern of peak temperature data is encoded in RL during heating. The data imply that there are sites in which the rare earth and charge stabilizing defects are closely associated within the host lattice, and the stability of the entire complex is linked to the lattice distortions from inclusions of impurities.
I. INTRODUCTION
For half a century thermoluminescence (TL or TSL) dosimetry has been crucial for both individual and environmental radiation monitoring. Many successful materials have been discovered that include aspects of high sensitivity, reliability, chemical and thermal stability, as well as ease of production and economic commercial availability. Examples of TL dosimetry materials include Mg2SiO4:Tb, Al2O3:C, CaSO4:Tm, CaSO4:Dy, Li2B4O7:Mn, and LiF TLD-100.1 Of particular potential interest, because of its high sensitivity, magnesium orthosilicate is doped with terbium (Mg2SiO4:Tb). This phosphor was first considered for radiation dosimetry in 1971.2,3 One key benefit is its high gamma sensitivity, which is 40–100 times that of LiF:Mg,Ti. Once manufactured, it only requires a simple annealing treatment (500° for half 1 h) for reactivation and it has excellent signal stability. Since it is mostly formed of relatively
Contributing Editor: Winston V. Schoenfeld a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2015.329 J. Mater. Res., Vol. 30, No. 22, Nov 27, 2015
light elements its effective atomic number is approximately 11, and so is also useful in environmental and personnel monitoring.4 An equally relevant feature is that the emission is in the blue end of the spectrum where the photomultiplier detectors are particularly responsive. Several investigations have already been carried out on phosphor: i.e., optical and thermal
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