Absorption and luminescence spectra and luminescence lifetime of silicate (SiO₂-Al₂O₃, SiO₂-Al₂O₃-MgO and SiO₂-Ga₂O₃) optical fibers with chromium-doped core fabricated by MCVD are studied. For the first time, the broadband luminescence of Cr⁴⁺ ions was observed at room temperature with a quantum yield of the order of 0.001%. Luminescence is represented as a band centered at 1100 nm with a bandwidth of 300 nm. After annealing at 1000 C during 6-8 hours a strong luminescence band appears with a maximum at 800-850 nm (depending on the sample) and a bandwidth of 200 nm, the luminescence quantum yield reaching 10%. Luminescence lifetime is about 18-26 microseconds (depending on the sample) at room temperature and does not change essentially at 77 K. The luminescence occurred after annealing is caused by Cr³⁺ ions mainly. The absorption spectra show a recharging of chromium ions after annealing expressed in an essential increase of Cr³⁺ ions concentration. Analysis of Raman scattering and X-ray diffraction of fiber preforms annealed in the same way has shown an emergence of a crystalline phase in the core of one of the annealed preforms. As a conclusion, the changes of the absorption and luminescence properties of the fibers after annealing are caused by the chromium ions recharging due to a rearrangement of their nearest environment. The results obtained in this paper appear to be a major step on the road to chromium-based tunable and ultrashort-pulse fiber lasers in the near IR region.