Gieszczyk Wojciech, Bilski Paweł, Mrozik Anna, Kłosowski Mariusz, Marczewska Barbara, Sas-Bieniarz Anna, Perzanowski Marcin, Zorenko Tetiana, Zorenko Yuriy
Institute of Nuclear Physics, Polish Academy of Sciences, Radzikowskiego 152, PL31342 Krakow, Poland.
Institute of Physics, Kazimierz Wielki University in Bydgoszcz, Powstancow Wielkopolskich 2, PL85090 Bydgoszcz, Poland.
Materials (Basel). 2020 Apr 27;13(9):2032. doi: 10.3390/ma13092032.
In this work, the luminescence properties of undoped, Tm doped, and Tb plus Tm double-doped crystals of the lithium magnesium phosphate (LiMgPO, 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 Tb and Tm 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 D-related Tb trapping sites and recombination took place at Tm-related sites, giving rise to the characteristic emission of Tm ions. At higher temperatures, above 300 °C, the electrons occupying the Tm-related trapping sites started to be released, and recombination took place at D-related Tb recombination centers, giving rise to the characteristic emission of Tb ions. The model explains the temperature dependence observed for the luminescence emission from double-doped LiMgPO crystals and may be fully applicable for the consideration of emissions of other double-doped compounds.
在本研究中，对磷酸锂镁（LiMgPO，LMP）化合物的未掺杂、铥（Tm）掺杂以及铽（Tb）和铥（Tm）共掺杂晶体的发光特性进行了研究。所研究的晶体采用微下拉法从熔体中生长。使用阴极发光、放射发光、光致发光和热释光方法研究了这些晶体的本征发光和掺杂相关发光。对Tb和Tm离子的共掺杂进行了分析，因为预计这些掺杂剂会表现出相反的俘获性质，即分别产生空穴俘获位点和电子俘获位点。未掺杂样品的测量光谱显示出三个突出的宽发射带，其最大值分别在约3.50、2.48和1.95 eV处，这与所研究化合物内部的本征结构缺陷有关。由于阴离子空位形成类F中心并俘获电子，预计会出现这种情况。Tb和Tm共掺杂晶体的测量光谱显示出与这些掺杂剂的4f-4f跃迁相对应的特征峰。提出了一种复合机制的简化模型来解释所测量的热释光光谱的温度依赖性。似乎在低温（低于300℃）下，电荷载流子从与D相关的Tb俘获位点释放，并在与Tm相关的位点发生复合，从而产生Tm离子的特征发射。在高于300℃的较高温度下，占据与Tm相关俘获位点的电子开始释放，并在与D相关的Tb复合中心发生复合，从而产生Tb离子的特征发射。该模型解释了共掺杂LiMgPO晶体发光发射的温度依赖性，并且可能完全适用于考虑其他共掺杂化合物的发射。
