Effect of Cr 3+ concentration on structural and optical properties of TiO 2 :Cr 3+ anatase and rutile phases

Abstract TiO 2 powders doped with different amounts of Cr 3+ ions (from 0 to 10 mol%) have been prepared by hydrothermal technique. TiO 2 :Cr 3+ powders were characterized by X-ray diffraction, Raman spectroscopy, transmission electron microscopy, diffuse reflection, absorption, photoluminescence and photoluminescence excitation spectra. The results showed that the Cr 3+ dopant concentrations did not affect on the lattice constants of TiO 2 crystal, but affected on shift and broadening of the Raman modes for both anatase and rutile phases. The band gap of both the anatase and rutile TiO 2 host lattice was strongly decreased with increasing Cr 3+ dopant concentration. The photoluminescence spectra of TiO 2 :Cr 3+ anatase phase exhibited a weak narrow peak (the so-called R-line) at 698 nm, meanwhile those of TiO 2 :Cr 3+ rutile phase consisted of a very intense narrow zero-phonon R-line at 695 nm assigned to the 2 E( 2 G) → 4 A 2 ( 4 F) transition of Cr 3+ ions in strong octahedral field and its phonon-sidebands. In particular, in the PL spectrum of TiO 2 :Cr 3+ rutile phase is also observed an abroad emission band centered at 813 nm assigned to the 4 T 2 ( 4 F) → 4 A 2 ( 4 F) transition of ions Cr 3+ in weak octahedral field.