Effective room-temperature luminescence in annealed chromium-doped silicate optical fibers

The influence of annealing at 1000 °C on the absorption and luminescence spectra of chromium in aluminosilicate and gallium silicate fibers at temperatures of 77 and 300 K is investigated. The spectra of initially weak luminescence with a maximum at 1100 nm and a quantum yield of approximately 10^-5 at 300 K shift to the 790-880-nm range in annealed fibers. After annealing the quantum yield increases by as much as 10%. The luminescence lifetime is found to be approximately 20 μs. The luminescence changes are explained by a rearrangement of the nearest environment and recharge of chromium ions (Cr⁴⁺ to Cr³⁺). The results obtained hold promise for the creation of tunable and ultrashort pulse fiber lasers.