Abstract
Scintillators are one of the luminescent materials which have a function to convert the ionizing radiation to UV-NIR photons. Among such applications, scintillators for thermal neutron detectors have attracted much attentions in recent years since the lack of 3He gas causes some serious problems in this field. To develop the alternative to 3He gas, many groups are developing new scintillators containing 6Li or 10B since these elements have a high cross section against thermal neutrons. For this purpose, we have developed Ce- [1] and Eu-doped [2] LiCaAlF6 crystals. In addition to scintillators, dosimeter materials are also important, and these materials are used in the individual and environmental dose monitors. In dosimeters, optically stimulated luminescence (OSL), thermally stimulated luminescence (TSL), and radiophotoluminescence (RPL) have played an important role. In dosimeter materials, human tissue equivalency is one of the most important properties, and LiCaAlF6 crystals are interesting because the effective atomic number of this material is close to the human tissue. If the dosimeter materials have the same effective atomic number with the tissue, ideally no mathematical corrections are required to calibrate the dose. Furthermore, the complementary relation of scintillators and dosimeter materials was found by us [3, 4] so the investigation of these properties on the same material is important to develop high performance materials for ionizing radiation detectors and to understand the energy migration process from the host matrix to emission centers.
In this work, we have grown Ce and Eu differently doped LiCaAlF6 crystals to investigate optical, scintillation, OSL and TSL properties. In transmittance, absorption was proportional to dopant concentrations and typical optical quantum yield of Ce and Eu-doped LiCaAlF6 were 40 and 100%, respectively. Scintillation wavelength and decay time profiles were investigated under X-ray irradiation. Ce3+ and Eu2+ 5d-4f luminescence appeared around 300 nm and 370 nm with typical decay time of 40 ns and 1.5 ms, respectively. OSL of Ce-doped ones appeared under 405 nm stimulation and that of Eu-doped ones was observed under 470 nm stimulation. TSL of Ce- and Eu-doped LiCaAlF6 were enough strong and they exhibited good response function from 1 to 1000 mGy exposure. In Eu-doped LiCaAlF6, the clear relation between the scintillation and dosimeter properties were observe while it was not observed in Ce-doped ones.
[1] T. Yanagida, et al., Opt. Mater. 32 311 (2009).
[2] T. Yanagida, et al., Opt. Mater., 33 1243 (2011).
[3] T. Yanagida, et al., Rad. Meas., 71 162 (2014).
[4] T. Yanagida, J. Lumin., 169 544 (2016).