Abstract
The upconversion luminescence of several YbEr co-doped Zr-Ba-La-Al-Na (ZBLAN) glass samples (Er(0.5)Yb(3):ZBLAN, Er(0.5)Yb(1):ZBLAN and Er(0.5):ZBLAN) has been studied. A new kind of upconversion cooperative radiation fluorescence, which comes from coupled cluster states of two Yb3+ ions has been observed. This is significant in that it may lead to a new path to achieve blue upconversion luminescence, which has promising upconversion applications.