Effect of carbon-dopant on the optical band gap and photoluminescence properties of [Ba0.5Sr0.5]TiO3 powders synthesized by the sol–gel process

Abstract

In this paper we studied the effect of carbon-doped on the optical band gap and photoluminescence properties of barium strontium titanate powders, [Ba0.5Sr0.5]TiO3 (BST), that synthesized via the sol–gel process with internal carbon sources, i.e., methanol, ethanol, and 1-butanol acting as a solvent. The types of solvent governed on the in-gap mechanism of C-doped BST powders. The Ti4+ ions substitution with partial C4+ ions was clearly proved by Fourier transform infrared spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy (XPS). As-synthesized pure BST powders were less weight losses and the carbonate species not observed. Indirect band gap of BST powders was examined by ultraviolet–visible spectroscopy. A possible in-gap mechanism between valence band maximum and conduction band minimum of BST powders was investigated by photoluminescence (PL) behavior. The PL emissions of pure BST powders appeared in five processes at 3.15, 2.95, 2.80, 2.55 and 2.33eV, whereas the C-doped BST powder did not appear at 2.95eV. Since the strong interaction of C–O bonds appeared that have been shared electrons of OåCåO bonds rather than transferred in the octahedral [TiO6] clusters. XPS and electron paramagnetic resonance spectra revealed the amount of oxygen deficiency was considerably formed by the long chain alcohol, while the short chain alcohol exhibited low amount. Besides that, (Ba+Sr)/Ti and (TiO5–VOX)/(TiO6) ratio increased gradually as molecular weight of alcohol.