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

The possibility of band gap engineering (BGE) in RAlO (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, , 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 reduction from ∼8.5 to ∼5.5 eV in RAlO perovskites with increasing R ionic radius was confirmed by the DFT electronic structure calculations performed for RMO crystals (R = Lu, Y, La; M = 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:Mn 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) were considered to be formed by the energy level of oxygen vacancy (V) with different arrangement of neighboring Y and V, while shallower electron traps of 0.9-1.0 eV were related to the energy level of Y antisite complexes with neighboring V or (V + V). The effect of the lowering of electron trap depths in RAlO was demonstrated for the V-related level of the (Y + V + V) complex defect for the particular case of La substituting Y.