Broadband Luminescence And Optical Amplification Of Transparent Ni～(2+)-doped Glass-ceramics

Recently, transparent Ni²⁺-doped glass-ceramics have received much attention. They exhibit broadband emission in the near infrared wavelength region over the optical telecommunication range in the case of 980 nm excitation, and they also possess long fluorescent lifetime, these excellent properties make them promising as gain medium for broadband optical amplifiers.The recent research progress of transparent Ni²⁺ -doped glass-ceramics is introduced in this thesis, and the potential applications and the future development of the luminescent materials are also discussed. Ni²⁺-doped petalite-type crystallites, MgAl₂O₄ crystallites in transparent glass-ceramics of MgO-Al₂O₃-SiO₂system and LiAlSiO₄ crystallites in transparent glass-ceramics of Li₂O-Al₂O₃-SiO₂ system have been successfully prepared. In order to increase the infrared broadband luminescent efficiencies of Ni²⁺-doped glass-ceramics and realize broadband optical amplification, the correlation among microstructure, heat-treatment and luminescence behaviors have been systematicly studied.The thermal stabilities of Ni²⁺-doped glasses have been investigated. â–³T (T_x- T_g) is usually used as an index of the thermal stability against crystallization of glass, the larger the value of AT, the better thermal stability of the glass. The AT of MgO-Al₂O₃-SiO₂ glass system is larger than 100℃, whereas the AT of Li₂O-Al₂O₃-SiO₂ glass system is less than 100℃, so it is easy to crystallize.The average crystallites size has been evaluated from the XRD data by using Scherrer equation. Due to much smaller size of precipitated crystallites than the visible wavelength, therefore, the scattering of visible photons by crystallites is negligible, and the glass-ceramics still remain transparency after heat-treatment. The crystallites size increases with increasing temperature.After crystallization, the absorption band slightly shifts to lower wavelength, and the local environment around the optically active ions Ni²⁺ have been changed. Ni²⁺ ions move into crystalline phases from the glass matrix, the crystal field strength ofoctahedral Ni²⁺ ions intensified. According to absorptions spectra, it is found that the absorption bands of Ni²⁺-doped glasses could be attributed to the transitions of the trigonal bipyramid fivefold Ni²⁺, while the absorption bands of Ni²⁺-doped glass-ceramics are caused by the transitions of Ni²⁺ in octahedral sites.The Ni²⁺-doped as-made glass does not show any emission in near infrared region, but after heat treatment, broadband infrared luminescence over the optical telecommunication range of 1200～1600 ran attributed to the ³T₂(F) →³A₂(F) transition of octahedral Ni²⁺ ions is observed in the case of 980 nm excitation. This result suggests that Ni²⁺ ions are located in octahedral coordination sites of crystallites in glass-ceramics.Optical amplification phenomenon of Ni²⁺-doped MgAl₂O₄ glass-ceramics has been observed. The effect of seed beam wavelength and excitation power on the absorption and optical gain has been revealed. The optical gain profile shows a close resemblance to the fluorescence spectrum, the gain decreases with increasing seed beam wavelength over the wavelengths of 1288～1350nm. The probe beam wavelength is fixed at 1288nm and the 980nm launched pump power changes from 0.3W to 1.28W, the optical gain increases linearly with excitation power.For the Li₂O-Al₂O₃-SiO₂ system, the effect of heat-treatment temperature, time andNi²⁺ doping concentration on the luminescence behaviors has been investigated. (1) As the temperature goes up, the intensity of broadband emission decreases and the peak position shifts to lower wavelength. (2) With the heat-treatment time prolongs, the intensity of broadband emission increases and the peak position shifts to lower wavelength. (3) As the Ni²⁺ doping concentration increases, the intensity of broadband emission decreases and the peak position shifts to longer wavelength.