Cr doped TiO_2 rutile nanoparticles have been used as precursor of microrods and microtubes grown by a vapor-solid method. The grown microstructures have nearly square cross-sections of a few microns wide and lengths of up to about 100 microns. By longer thermal treatments or higher growth temperatures, the ratio of microrods to microtubes increases. The presence of partially filled openings with growth steps in the internal faces of the tubes indicates that the tubes transform into rods by extended or intense thermal treatments, which enables to control the nature of the microstructures, tubes or rods, by varying the parameters of the thermal treatment. Cr incorporation has been found to be homogeneous along the growth axis, with amounts in the range from 1.2 to 2.8% of cationic fraction, which depend on the Cr content in the precursor and on the growth parameters. Optical activation of the Cr ions has been demonstrated by cathodoluminescence in the scanning electron microscopy, and crystallographic assessment of the structures has been carried out using Raman spectroscopy and electron backscattered diffraction.