posted on 2021-11-23, 21:04authored byYaroslav Zhydachevskyy, Yuriy Hizhnyi, Sergii G. Nedilko, Irina Kudryavtseva, Vladimir Pankratov, Vasyl Stasiv, Leonid Vasylechko, Dmytro Sugak, Aleksandr Lushchik, Marek Berkowski, Andrzej Suchocki, Nickolai Klyui
The possibility of band gap engineering (BGE) in RAlO3 (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, Eg, 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 Eg reduction from ∼8.5 to ∼5.5 eV in RAlO3 perovskites with increasing R3+ ionic radius was confirmed
by the DFT electronic structure calculations performed for RMIIIO3 crystals (R = Lu, Y, La; MIII =
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)AlO3:Mn4+ 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 YAlO3) were considered to
be formed by the energy level of oxygen vacancy (VO) with
different arrangement of neighboring YAl and VY, while shallower electron traps of 0.9–1.0 eV were related
to the energy level of YAl antisite complexes with neighboring
VO or (VO + VY). The effect of the
lowering of electron trap depths in RAlO3 was demonstrated
for the VO-related level of the (YAl + VO + VY) complex defect for the particular case of
La substituting Y.