Luminescence of Cr4+:Ca2GeO4 films in the near infrared region

The Cr⁴⁺:Ca₂GeO₄ films are produced on fused silica substrates by the method of RF magnetron sputtering. Both initial films and those annealed in air at temperatures below 700°C are amorphous. The films annealed at temperatures from 500 to 700°C exhibit luminescence in the wavelength range from 1200 to 1400 nm upon laser excitation at 980 nm, which suggests that they contain tetravalent chromium ions.