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

Yaroslav Zhydachevskyy; Yuriy Hizhnyi; Sergii G Nedilko; Irina Kudryavtseva; Vladimir Pankratov; Vasyl Stasiv; Leonid Vasylechko; Dmytro Sugak; Aleksandr Lushchik; Marek Berkowski; Andrzej Suchocki; Nickolai Klyui

doi:10.1021/acs.jpcc.1c06573

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

J Phys Chem C Nanomater Interfaces. 2021 Dec 9;125(48):26698-26710. doi: 10.1021/acs.jpcc.1c06573. Epub 2021 Nov 23.

Authors

Affiliations

¹ Institute of Physics, Polish Academy of Sciences, aleja Lotników 32/46, Warsaw 02-668, Poland.
² Lviv Polytechnic National University, S. Bandera Str. 12, Lviv 79013, Ukraine.
³ Taras Shevchenko National University of Kyiv, Volodymyrska Str. 60, Kyiv 01033, Ukraine.
⁴ Institute of Physics, University of Tartu, W. Ostwald Str. 1, Tartu 50411, Estonia.
⁵ Institute of Solid State Physics, University of Latvia, Kengaraga Str. 8, Riga 1063, Latvia.
⁶ College of Physics, Jilin University, 2699 Qianjin Str., Changchun 130012, China.
⁷ V.E. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine, 41 prospekt Nauki, Kyiv 03028, Ukraine.

Abstract

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, 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 RAlO₃ perovskites with increasing R³⁺ ionic radius was confirmed by the DFT electronic structure calculations performed for RM^IIIO₃ 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)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 (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 RAlO₃ 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.