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

Abstract

The possibility of band gap engineering (BGE) in RAlO 3 (R = Y, La, Gd, Yb, Lu) perovskites in the context of trap depths of intrinsic point defects was investigated comprehensively using experimental and theoretical approaches. The optical band gap of the materials, E g , was determined via both the absorption measurements in the VUV spectral range and the spectra of recombination luminescence excitation by synchrotron radiation. The experimentally observed effect of E g reduction from ∼8.5 to ∼5.5 eV in RAlO 3 perovskites with increasing R 3+ ionic radius was confirmed by the DFT electronic structure calculations performed for RM III O 3 crystals (R = Lu, Y, La; M III = Al, Ga, In). The possibility of BGE was also proved by the analysis of thermally stimulated luminescence (TSL) measured above room temperature for the far-red emitting (Y/Gd/La)AlO 3 :Mn 4+ phosphors, which confirmed decreasing of the trap depths in the cation sequence Y → Gd → La. Calculations of the trap depths performed within the super cell approach for a number of intrinsic point defects and their complexes allowed recognizing specific trapping centers that can be responsible for the observed TSL. In particular, the electron traps of 1.33 and 1.43 eV (in YAlO 3 ) were considered to be formed by the energy level of oxygen vacancy (V O ) with different arrangement of neighboring Y Al and V Y , while shallower electron traps of 0.9–1.0 eV were related to the energy level of Y Al antisite complexes with neighboring V O or (V O + V Y ). The effect of the lowering of electron trap depths in RAlO 3 was demonstrated for the V O -related level of the (Y Al + V O + V Y ) complex defect for the particular case of La substituting Y.

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

“…Trap III, with an activation energy of 1.7 eV, is the deepest intrinsic trap which becomes dominant in the YAlO 3 crystals grown from Y-rich composition. Therefore, we believe that it is related to the Y Al antisites stabilized by some neighboring defects (as postulated in ref ). The nature of this probably complex center cannot be determined in this study.…”

“…Recent calculations point out, however, that the complexes of Y Al antisites with such defects as O i , V O , V Y , or V Al may form deeper traps. 25 Ab initio calculations of the electronic structure of Mn Al 3+ -and Mn Y 2+ -doped YAP have been also reported, showing multiple energy levels introduced by doping into the YAP band gap. 26,27 In order to get a better insight into the recharging processes of Mn 2+ ions in the YAP lattice and their influence on green TL, YAP crystals doped mainly with manganese in the 2+ oxidation state are required.…”

“…The Y Al 2+ centers stabilized either by oxygen vacancies or defects, such as some metal impurity in the nearest-neighbor Y site, were also confirmed by luminescence studies. , The Y Al antisites are also known to be responsible for the radiation-induced coloration of YAP crystals. − Calculations using density functional theory confirm the electron trapping ability of isolated Y Al or V O defects, as well as Y Al –V O complexes. − These theoretical studies confirm also that the isolated Y Al antisites produce electron traps that are not deep enough to be responsible for the TL peaks at 400 or 450 K in YAP. Recent calculations point out, however, that the complexes of Y Al antisites with such defects as O i , V O , V Y , or V Al may form deeper traps . Ab initio calculations of the electronic structure of Mn Al 3+ - and Mn Y 2+ -doped YAP have been also reported, showing multiple energy levels introduced by doping into the YAP band gap. , …”

First-principles studies of defect behaviour in bismuth germanate

“…The trivalent Bi cation has a suitable ionic size to accommodate the REE ion and has been found to influence properties of scintillators 44 . This makes them suitable dopants for the BGO system 22 .…”

Structural and Optical Properties of High Entropy (La,Lu,Y,Gd,Ce)AlO3 Perovskite Thin Films

“…Such phenomena can be observed through shifts in thermally stimulated luminescence (TSL) spectra. [ 24 ] Bandgap and trap‐level engineering can be beneficial for much‐improved transfer efficiency. The system, however, can be very complex as the trapping of luminescent centers (hole/electron) shows opposite TSL shifting with respect to the altered A‐site concentrations as well as variation in the ratio of electric/magnetic dipole transitions.…”