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

Abstract

In this work, the luminescence properties of undoped, Tm3+ doped, and Tb3+ plus Tm3+ double-doped crystals of the lithium magnesium phosphate (LiMgPO4, LMP) compound were investigated. The crystals under study were grown from melt using the micro-pulling-down method. The intrinsic and dopant-related luminescence of these crystals were studied using cathodo-, radio-, photo-, and thermoluminescence methods. Double doping with Tb3+ and Tm3+ ions was analyzed as these dopants are expected to exhibit an opposite trapping nature, namely to create the hole and electron-trapping sites, respectively. The spectra measured for the undoped samples revealed three prominent broad emission bands with maxima at around 3.50, 2.48, and 1.95 eV, which were associated with intrinsic structural defects within the studied compound. These were expected due to the anion vacancies forming F+-like centers while trapping the electrons. The spectra measured for Tb and Tm double-doped crystals showed characteristic peaks corresponding to the 4f–4f transitions of these dopants. A simplified model of a recombination mechanism was proposed to explain the temperature dependence of the measured thermally stimulated luminescence spectra. It seems that at low temperatures (below 300 °C), the charge carriers were released from 5D3-related Tb3+ trapping sites and recombination took place at Tm-related sites, giving rise to the characteristic emission of Tm3+ ions. At higher temperatures, above 300 °C, the electrons occupying the Tm3+-related trapping sites started to be released, and recombination took place at 5D4-related Tb3+ recombination centers, giving rise to the characteristic emission of Tb3+ ions. The model explains the temperature dependence observed for the luminescence emission from double-doped LiMgPO4 crystals and may be fully applicable for the consideration of emissions of other double-doped compounds.

Дефекты и перенос энергии в Sr-=SUB=-9-=/SUB=-Lu(PO-=SUB=-4-=/SUB=-)-=SUB=-7-=/SUB=-, легированном ионами Pr-=SUP=-3+-=/SUP=-

“…Потенциально люминесценция в этой области спектра может быть связана с проявлением АЛЭ. Имеются литературные данные о люминесценции АЛЭ в некоторых фосфатах: например, в YPO 4 эмиссия АЛЭ в спектре ФЛ находится в области ∼ 23800 cm −1 (∼ 450 nm) [18], в LiY(PO 4 ) 3 -в области ∼ 22600 cm −1 (∼ 470 nm) [19], в LiMgPO 4 -в области ∼ 350 nm [20], в AlPO 4 полоса эмиссии АЛЭ имеет максимум при 2.95 eV (420 nm) [17]. Однако для интерпретации полосы 350 nm, как эмиссии АЛЭ в исследуемом широкощелевом Sr 9 Lu(PO 4 ) 7 , требуется измерение спектров возбуждения ФЛ вплоть до области края фундаментального поглощения и межзонных переходов в вакуумной ультрафиолетовой области.…”

Uniformity of Thermoluminescence and Optically Stimulated Luminescence Signals Over the Length of Doped LiMgPO4 Crystal Rods Grown by Micro-Pulling-Down Method

“…The LMP compound was shown to have a high radiosensitivity and a broad linear dose–response range [ 3 ]. Numerous research articles on luminescent properties of LMP doped with different elements have been published since 2010 [ 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 ]. The LMP crystal codoped with terbium (Tb) and boron (B) has been most extensively studied, but other rare earth dopants such as Sm, Tm, and Eu have also been tested [ 5 , 10 , 13 , 20 ].…”