Absolute quantum cutting efficiency of Tb³⁺-Yb³⁺ co-doped glass

The absolute quantum cutting efficiency of Tb³⁺-Yb³⁺ co-doped glass was quantitatively measured by an integrating sphere detection system, which is independent of the excitation power. As the Yb³⁺ concentration increases, the near infrared quantum efficiency exhibited an exponential growth with an upper limit of 13.5%, but the visible light efficiency was reduced rapidly. As a result, the total quantum efficiency monotonically decreases rather than increases as theory predicted. In fact, the absolute quantum efficiency was far less than the theoretical value due to the low radiative efficiency of Tb³⁺ (<61%) and significant cross-relaxation nonradiative loss between Yb³⁺ ions.