Near and mid-infrared emissions implications of hydroxyl groups in Er³⁺-doped tellurite glasses: enhancing luminescent properties via purification processes

Tellurite glasses are increasingly attracting interest from the photonics industry due to their promising spectroscopic properties. However, intrinsic absorption losses caused by impurities, especially hydroxyl groups (OH^-) remain a significant challenge for achieving efficient infrared emission. This work presents what we believe to be a new purification method for Er³⁺-doped tellurite glasses using diethyl zinc to treat oxide precursors. Glasses with the composition 69.7 TeO₂ - 25 ZnO - 5 La₂O₃ - 0.3 Er₂O₃ (mol %) were fabricated at each step of the purification and characterized. The effect of the purification in the reduction of OH content is evidenced in the decreased absorption coefficient from 2.57 to 0.22 cm^-¹ at 3300 nm after applying the chemical treatment, which accounted for a decrease in the number of OH ions/cm³ from 2.88 × 10¹⁹ to 2.70 × 10¹⁸. The purification process significantly improved the optical properties, enabling consecutive emissions at 1535, 2700, and 3280 nm when pumped with an optical parametric oscillator (OPO) laser tuned to 522 nm. With the reduction of OH content, there was an increase in the emission efficiency from 78.6 to 93.9% and 7.3 to 10.7% for the emissions for ⁴I_13/2→⁴I_15/2 and ⁴I_11/2→⁴I_13/2, respectively.