Effect of Yb 3+ ‐Codoping on the Upconversion Emission Intensity in Er 3+ ‐Doped ZBLAN Fluoride Glasses under 800‐nm Excitation

The effect of Yb 3+ ‐codoping on the upconversion emission intensity in Er 3+ ‐doped ZBLAN fluoride glasses is investigated. The codoping of Yb enhanced the emission intensity for the samples excited by an 800‐nm laser diode beam. The enhancement in a constant YbF 3 content (2 mol%) increased with increasing ErF 3 content was about 70% of the initial value at 550 nm for the glasses containing 8 mol% of ErF 3 . The emission intensity at 550 nm in a constant ErF 3 content (5 mol%) increased remarkably with the addition of YbF 3 and was maximized around 7 mol% of YbF 3 content, giving an increased ratio of about 200% of the initial value. The reason for the enhancement is discussed and it is derived mainly from two‐step excitation of Er 3+ assisted by Yb 3+ excited through the energy transfer from Er 3+ .