Dynamic process of self-trapped polaron in photoexcited SrTiO3

Efficacy of the DFT + U formalism for modeling hole polarons in perovskite oxides

“…The formation energies computed using LDA+U with U (O 2p) = 8 eV for a 2 × 2 × 2 Monkhorst-Pack mesh are ∆E f = −0.09 eV and ∆ E f = −0.14 eV, in good agreement with the values of ∆E f = −0.09 eV and ∆ E f = −0.16 eV obtained using the HSE06 hybrid functional, where the latter calculations required more than two orders of magnitude more computer time. We can compare these values with results from a model Hamiltonian approach, 9,10 which was parametrized using primarily experimental data. The authors obtained an energy gain of −0.2 eV upon STH formation, which is in reasonable agreement with the present data.…”

“…Polaronic effects in these materials have been discussed for some time 1,6 and have also been investigated theoretically. [7][8][9][10] While the existence of "bound" small hole polarons 11 , which are associated for example with acceptor defects in oxides, is well established the presence of "free" (or self-trapped) polarons in oxides, which are naturally also much harder to observe, has been doubted. 1 By contrast earlier computational studies did identify polarons in BaTiO 3 based on embedded cluster Hartree-Fock (HF) calculations 7,8 and SrTiO 3 based on a suitably parametrized many-body model Hamiltonian.…”

“…1 By contrast earlier computational studies did identify polarons in BaTiO 3 based on embedded cluster Hartree-Fock (HF) calculations 7,8 and SrTiO 3 based on a suitably parametrized many-body model Hamiltonian. 9,10 This provides the motivation for the present work, in which we explore self-trapped hole (STH) polarons in three prototypical oxidic perovskites, SrTiO 3 , BaTiO 3 , and PbTiO 3 . As will be discussed in detail below the description of polaronic effects is sensitive to the level of theory that is being employed.…”

Blue luminescence of SrTiO3 under intense optical excitation

“…The greenish luminescence (GL) having a maximum at 2.2-2.4 eV of photon energy (wavelength λ ≈ 500 nm) that is emitted by pure STO at low temperature under exposure to UV or X-ray radiation has been known since a long time, 12,13,14 and is generally ascribed to the decay of intrinsic self-trapped excitons (STE). 15,16,17,18 A STE can be roughly depicted as a tightly bound state of a hole and a Ti 3+ polaron. 19,20 However, this purely intrinsic scenario has been recently called into question by Mochizuki et al, 21,22 who argued for a crucial role of defects and possibly of surfaces in this GL emission.…”