In-Gap States in Wide-Band-Gap SrTiO3 Analyzed by Cathodoluminescence

Abstract

The cathodoluminescence spectra between 300 and 900 nm were investigated for undoped and Nb2O5-doped SrTiO3 sintered both in air and under low oxygen partial pressure ( ). Two broadened emission peaks observed experimentally were deconvoluted into five luminescences in the visible range of 2.9 eV (427 nm) to 2.4 eV (516 nm), and in the infrared range of 1.57 eV (790 nm), 1.55 eV (800 nm), and 1.44 (861 nm); each of which was assigned to interband transitions between in-gap energy states correspondingly by considering the intrinsic and extrinsic defect reactions. It is suggested that the 2.4 eV emission originated from charge transfer between Ti4+ and O2− by a mechanism of charge-transfer vibronic excitons. The 2.9 eV luminescence was due to electrons trapped in the donor states of extrinsic NbTi• generated by donor doping, and of extrinsic VO•• produced by low- sintering, and of the Schottky intrinsic VO•• in undoped samples deexciting directly to the valence band. The triplet of (1.57+1.44) and 1.55 eV was from the emissions between the Schottky intrinsic defects in SrTiO3 and in second-phase TiO2, respectively.