Uniform Al2O3:Cr3+ microfibers were synthesized by using a hydrothermal route and thermal decomposition of a precursor of Cr3+ doped ammonium aluminum hydroxide carbonate (denoted as AAHC), and characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), photoluminescence (PL) spectra and decay curves. XRD indicated that Cr3+ doped samples calcined at 1473 K were the most of alpha-Al2O3 phase. SEM showed that the length and diameter of these Cr3+ doped alumina microfibers were about 3-9 mu m and 300 nm, respectively. PL spectra showed that the Al2O3:Cr3+ microfibers presented a broad R band at 696 nm. It is shown that the 0.07 mol% of doping concentration of Cr3+ ions in alpha-Al2O3:Cr3+ was optimum. According to Dexter's theory, the critical distance between Cr3+ ions for energy transfer was determined to be 38 angstrom. It is found that the curve followed the single-exponential decay. (c) 2012 Elsevier Ltd. All rights reserved.