Efficient upconversion luminescence from Ba5Gd8Zn4O21:Yb(3+), Er(3+) based on a demonstrated cross-relaxation process.

Under 971 nm excitation, bright green and red emissions from Yb(3+)/Er(3+) co-doped Ba5Gd8Zn4O21 phosphor can be observed, especially the intense red emission in highly doped samples. The experimental results indicate that Ba5Gd8Zn4O21:Yb(3+), Er(3+) emits stronger upconversion luminescence than NaYF4:Yb(3+), Er(3+) under a low excitation power, and a maximum upconversion power efficiency of 2.7% for Ba5Gd8Zn4O21:Yb(3+), Er(3+) was achieved. More significantly, to explain the red emission enhanced with the dopant concentration, this paper presents a possible cross-relaxation process and demonstrates it based on the rate equation description and temporal evolution. In view of the strong upconversion luminescence, colour tunable ability and stable chemical nature, Yb(3+)/Er(3+) co-doped Ba5Gd8Zn4O21 phosphor could be an excellent candidate for efficient upconversion luminescence generation.