Electron Paramagnetic Resonance and Optical Studies of Thermoluminescence Processes in Mn-Doped YAlO<sub>3</sub> Single Crystals
H. Przybylińska, Yaroslav Zhydachevskyy, Aneta Grochot, Agnieszka Wołoś, Vasyl Stasiv, M. Głowacki, Agata Kamińska, S. Ubizskii, M. Berkowski, A. Suchocki
Abstract
A detailed electron paramagnetic resonance (EPR), optical absorption, luminescence, and thermoluminescence (TL) study of Mn-doped YAlO3 (YAP) single crystals was performed. The crystals were grown by the Czochralski method from stoichiometric (Y/Al = 1) and yttrium-rich (Y/Al = 1.04) melts and codoped with either Si or Hf ions. The EPR measurements revealed the presence of only one type of Mn2+ center, that is, isolated Mn ions occupying Y sites (MnY2+). It was found that only in yttrium-rich crystals, the MnY2+ ions undergo recharging to MnY3+ under ionizing irradiation, indicating that this process requires the availability of sufficiently deep electron traps. The initial charge state is fully restored only after subsequent warming above 600 K. The presented results demonstrate, moreover, that MnY3+ + e → MnY2+ recombination is not the most efficient excitation channel of the green 4T1 → 6A1 emission of MnY2+, possibly because of the huge energy difference between the recombination (>5.39 eV) and excitation (3 eV) energies. In contrast, energy transfer to MnY2+ proves to be dominant. A general model of trapping and recombination mechanisms responsible for TL of YAP:Mn crystals above room temperature is proposed. Besides MnY2+ ions and the defect-related electron and hole traps intrinsic to the YAP lattice, the model includes also unintentional dopants such as FeAl2+ acting as deep hole traps, as well as MnAl4+ and CrAl3+ ions acting both as deep hole and electron traps.