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

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.

Intrinsic and Dopant-Related Luminescence of Undoped and Tb Plus Tm Double-Doped Lithium Magnesium Phosphate (LiMgPO4, LMP) Crystals

“…The intensity of the UV emission band (354 nm) increased with temperature up to around 170 • C and then started decreasing. For temperatures higher than around 300 • C, this band was practically invisible and the whole measured luminescence originated from the second band (635 nm) [19]. The shape of the spectra did not change with increasing temperature and agreed very well with the RL spectrum measured at RT.…”

“…Meanwhile, we also note here that the band observed at around 355 nm probably resulted from a superposition of the 1 I 6 → 3 F 4 and 1 D 2 → 3 H 6 transitions, which could not be better resolved because of the low resolution (4 nm) of the applied spectrometer. Other less-intense transitions ascribed as characteristic for Tm 3+ ions [19] were also observed. The emissions of the Tb 3+ ions were not practically visible at this temperature range.…”

“…However, in the case of crystals, the situation may look slightly different. As reported many times [14][15][16][17][18][19], high-temperature crystallization changes the energetic distribution of TL-related electron traps in materials, which are strongly manifested in the observed differences between the glow-curves measured for materials in different forms (namely powders and crystals). This may be related to the creation of many different types of structural defects.…”

“…Recently, this material was also successfully crystallized from melt using a novel micro-pulling-down (MPD) crystal growth technique [14][15][16][17][18]. Further, the melt-grown crystals were found to show substantial advantages over samples in the form of powders [19], which were manifested as significantly reduced luminescence at the low-temperature range that may strongly affect the fading properties of this material.…”

Thermoluminescence Characteristics of Terbium Doped Zinc Borates

“…When the amount of Tb doping increases by 3%, the lattice parameter "a" and the unit cell volume slowly increase as the atomic radius of Tb is greater than that of Zn. When the doping amount is above 3%, the lattice parameter "a" and unit cell volume are reduced due to lattice distortion or migration of the doping ions to the interstitial positions [18]. In addition, the diffraction pattern of the ZnB2O4:0.10Tb 3+ sample indicates the presence of small impurity phases, which are H3BO3 and B2O3.…”