Transparent glass-ceramics based on Co~(~(2+)),Ga~(3+)-codoped ZnO nanocrystals: A promising nonlinear optical material

摘要

We report on fabrication, structure, spectroscopic and nonlinear properties of a new functional optical material -transparent glass-ceramics (GCs) based on Co~(2+),Ga~(3+)-codoped ZnO (Co~(2+):GZO) nanocrystals. The introduction of Ga~(3+) cations that are smaller than Zn~(2+) ones and have a different valence state, is expected to modify the crystal field around the Co~(2+) ions leading to broadband absorption at the ~4A_2(~4F) → ~4T_1(~4F) transition. The glass of the ZnO - K_2O - Al_2O_3 -SiO_2 system was doped with 3 mol% Ga_2O_3 and 0.05 mol% CoO. Transparent GCs were produced by secondary heat-treatments at 680 - 860 °C. They contained one crystalline phase - nanosized (8 - 26 nm) hexagonal GZO crystals, Ga~(3+) ions being distributed between the ZnO nanocrystals and the residual glass. The absorption spectra of GCs contained an intense band at 1.3-1.65 μm related to the ~4A_2(~4F) → ~4T_1(~4F) Co~(2+) transition in T_d sites. A rise of IR losses due to the free charge carrier scattering in GZO was observed. Absorption saturation of transparent GCs was studied at ~1.54 μm. They exhibited low saturation fluence, 0.7-1.3 ± 0.2 J/cm~2, and high laser-induced damage threshold, ~25 J/cm~2. Co~(2+),Ga~(3+)-codoped ZnO-based transparent GCs are promising for passive Q-switching of eye-safe erbium lasers emitting at ~1.5-1.7 μm.