Thermoluminescence Enhancement of LiMgPO4 Crystal Host by Tb3+ and Tm3+ Trivalent Rare-Earth Ions Co-doping.

Wojciech Gieszczyk,Paweł Goj,Paweł Bilski,Mariusz Kłosowski,Anna Mrozik,Paweł Stoch,Anna Sas-Bieniarz,Barbara Marczewska

doi:10.3390/ma12182861

Abstract

We investigated the influence of terbium and thulium trivalent rare-earth (RE) ions co-doping on the luminescent properties enhancement of LiMgPO4 (LMP) crystal host. The studied crystals were grown from the melt by micro-pulling-down (MPD) technique. Luminescent properties of the obtained crystals were investigated by thermoluminescence (TL) method. The most favorable properties and the highest luminescence enhancement were measured for Tb and Tm double doped crystals. A similar luminescence level can be also obtained for Tm, B co-doped samples. In this case, however, the low-temperature TL components have a significant contribution. The measured luminescent spectra showed a typical emission of Tb3+ and Tm3+ ions of an opposite trapping nature, namely the holes and electron-trapping sites, respectively. The most prominent transitions of 5D4 → 7F3 (550 nm for Tb3+) and 1D2 → 3F4 (450 nm for Tm3+) were observed. It was also found that Tb3+ and Tm3+ emissions show temperature dependence in the case of double doped LMP crystal sample, which was not visible in the case of the samples doped with a single RE dopant. At a low temperature range (up to around 290 °C) Tm3+ emission was dominant. At higher temperatures, the electrons occupying Tm3+ sites started to be released giving rise to emissions from Tb-related recombination centers, and emissions from Tm3+ centers simultaneously decreased. At the highest temperatures, emission took place from Tb3+ recombination centers, but only from deeper 5D4 level-related traps which had not been emptied at a lower temperature range.

Highlights

LiMgPO4 crystallizes in orthorhombic systems where tetrahedral PO4, octahedral LiO6, and MgO6 groups constitute the structure forming a 3D network
The LiMgPO4 powders of different dopants concentration were synthesized by a solid-state reaction in air
Because a standard powder diffraction procedure was applied, the obtained crystal samples were powdered before the measurements using the agate mortar

Summary

Introduction

LiMgPO4 crystallizes in orthorhombic systems where tetrahedral PO4 , octahedral LiO6 , and MgO6 groups constitute the structure forming a 3D network. This compound belongs to a large family of orthophosphates of general ABPO4 formula. Its structure depends on the relative size of the ions, namely, in case of LiMgPO4 , where the sizes of monovalent A (Li+ ) and divalent B (Mg2+ ) ions are relatively small, the final compound adopts the olivine structure. The structure contains tetrahedral PO4 and octahedral MgO6 and LiO6 groups which share edges and corners. More detailed structure specification of the studied compound can be found in [1]

Methods

Results

Conclusion