High Efficiency Infrared-to-Visible Upconversion Emission in Er³⁺,Yb³⁺, and Ho³⁺ Codoped Tellurite Glasses

A novel method of codoping the Er³⁺, Yb³⁺, and Ho³⁺ ions in tellurite glasses is demonstrated to obtain a high efficiency of infrared-to-visible upconversion. Three intense emission bands observed in Er³⁺, Yb³⁺, and Ho³⁺ codoped tellurite glasses centred at 525, 547, and 657nm correspond to Er³⁺: ²H_11/2 → ⁴I_15/2, Er³⁺: ⁴S_3/2 → ⁴I_15/2+Ho³⁺: ⁵S₂(⁵F₄) → ⁵ I₈, and Er³⁺: ⁴ S_3/20 → ⁴I_15/2+Ho³⁺: ⁵F₅ → ⁵I₈ transitions, respectively. No visible upconversion quenching phenomenon is observed when three rare-earth ions are codoped together in tellurite glasses. In contrast, the upconversion intensity of red and green emissions in Er³⁺, Yb³⁺, and Ho³⁺ codoped glasses is enhanced largely when compared with Er³⁺/Yb³⁺-codoped glasses. The dependence of upconversion intensities on excitation power and the possible upconversion mechanisms are evaluated. The three emissions are based on two-photon absorption processes.