Electron Paramagnetic Resonance and Optical Studies of Thermoluminescence Processes in Mn-Doped YAlO₃ Single Crystals

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 (MnY 2+). It was found that only in yttrium-rich crystals, the MnY 2+ ions undergo recharging to MnY 3+ 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 MnY 3+ + e → MnY 2+ recombination is not the most efficient excitation channel of the green 4T1 → 6A1 emission of MnY 2+, possibly because of the huge energy difference between the recombination (>5.39 eV) and excitation (3 eV) energies. In contrast, energy transfer to MnY 2+ 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 MnY 2+ ions and the defect-related electron and hole traps intrinsic to the YAP lattice, the model includes also unintentional dopants such as FeAl 2+ acting as deep hole traps, as well as MnAl 4+ and CrAl 3+ ions acting both as deep hole and electron traps.

Band Gap Engineering and Trap Depths of Intrinsic Point Defects in RAlO3 (R = Y, La, Gd, Yb, Lu) Perovskites

“…Despite the main experimental tendencies of the crystal band gaps and trap depths obtained for the Mn 4+ -doped samples (see previous sections), we do not consider in calculations presented here any Mn-related defects in perovskites. We believe that the TSL properties (namely, traps I and II) analyzed in the previous section are formed by native (intrinsic) defects of the crystal hosts and are not related to Mn impurity ions (for more details, see Przybylinśka et al 78 and references therein). Owing to the experimental results reported in refs 64−67, these are electron traps related, most probably, to Y Al antisites stabilized by some other intrinsic point defects.…”

“…As follows from the analysis of the TSL data presented above or available literature data, 50,52,78,79 the defects, which form the main high-temperature TSL peaks in YAlO 3 and YAlO 3 :Mn 4+ , usually have depths from 1.20 to 1.43 eV. It is commonly assumed that these defects are electron traps.…”

“…It is commonly assumed that these defects are electron traps. 50,[64][65][66][67]78 According to Table S5, none of the single point defects like Y Al , V O , O i , or V Y have energy levels of appropriate depth with respect to the CB to be responsible for the high-temperature TSL or the radiation-induced coloration of YAlO 3 crystals stable at room temperature. However, as our calculation results show, the trap depths of single defects can be considerably changed if the defects are complexed with each other.…”

“…As follows from the analysis of the TSL data presented above or available literature data, ,,, the defects, which form the main high-temperature TSL peaks in YAlO 3 and YAlO 3 :Mn 4+ , usually have depths from 1.20 to 1.43 eV. It is commonly assumed that these defects are electron traps. ,− , According to Table S5, none of the single point defects like Y Al , V O , O i , or V Y have energy levels of appropriate depth with respect to the CB to be responsible for the high-temperature TSL or the radiation-induced coloration of YAlO 3 crystals stable at room temperature. However, as our calculation results show, the trap depths of single defects can be considerably changed if the defects are complexed with each other.…”

Photon and Phonon Coherence to Enhance Photoluminescence by Magnetic Polarons in Mn-Doped Rb3Cd2Cl7 Perovskites

“…There are very few TL phenomena in halide perovskite systems in previous reports. However, the slow-release luminescence and TL phenomena formed by the doping of TMs in other systems have been reported. − , However, their mechanism is still not understood. So far, the physical mechanisms of TL induced by TM ions in halide perovskite systems have not been studied.…”