Publication No.72



R. Viteri, D. Ortiz, A. Stashans. Quantum chemical 
study of photo-excited states in tetragonal SrTiO3 - 
Phil. Mag., 2003, accepted.

Abstract:
	The nature of photo-excited states in SrTiO3 has 
been a topic of intense debate during the last decades. Using 
a quantum-chemical method developed for crystals, we present a 
theoretical interpretation to the structural and electronic 
properties of triplet excitons in the tetragonal SrTiO3 crystal. 
Our study demonstrates that the defect structure may correspond 
to the Mott-Wannier-type exciton having a considerable distance, 
2.14 �, between the hole and the electronic parts of the defect. 
The geometry optimization leads to extensive defective region 
containing up to five atoms. However, the obtained magnitudes of 
atomic movements do not exceed 0.15 �. It is also observed that 
the self-trapped exciton polarises the lattice around it. Using 
the so-called delta SCF method, the luminescence energy due to 
the exciton is found to be equal to 1.13 eV. As it corresponds 
to the infrared part of the spectrum, the experimentally detected 
green luminescence due to photo-excited states should be 
attributed to the singlet excitons.




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