Selective doping of Ni2+ in highly transparent glass-ceramics containing nano-spinels ZnGa2O4 and Zn1+x Ga2−2x Ge x O4 for broadband near-infrared fiber amplifiers

Abstract

Selective doping of Ni²⁺ in octahedral sites provided by nanocrystals embedded in glass-ceramics (GCs) is crucial to the enhancement of broadband near-infrared (NIR) emission. In this work, a NIR emission with a full-width-at-half-maximum (FWHM) of 288 nm is first reported from ZnGa₂O₄: Ni²⁺ nano-spinels embedded GCs with excellent transparency. A comparison is made of the NIR luminescence properties of Ni²⁺ doped GCs containing ZnGa₂O₄, germanium-substituted ZnGa₂O₄ nano-spinels (Zn_1+x Ga_2-2x Ge _x O₄), and Zn₂GeO₄/Li₂Ge₄O₉ composite nanocrystals that are free of Ga³⁺. The results show that ZnGa₂O₄: Ni²⁺ GCs exhibit a significantly enhanced NIR emission. The incorporation of the nucleating agent TiO₂ is favored in terms of the increased luminescence intensity and prolonged lifetime. The possible causes for the enhancement effect are identified from the crystal structure/defects viewpoint. The newly developed GCs incorporate good reproducibility to allow for a tolerance of thermal treatment temperature and hence hold great potential of fiberization via the recently proposed "melt-in-tube" method. They can be considered as promising candidates for broadband fiber amplifiers.