Preparation and optical properties of transparent tellurite based glass ceramics doped by Er³⁺ and Eu³⁺

Optically transparent Er³⁺ and Eu³⁺ doped (less than 1.5 mol% Er₂O₃ and Eu₂O₃) glass ceramics based on the system K₂O-MgO-Nb₂O₅-TeO₂ have been successfully prepared for the first time. Addition of Er³⁺ and Eu³⁺ is effective for the formation of a crystalline phase showing second harmonic generation. Fluorescence spectra of Er³⁺ and Eu³⁺ in glass ceramics are almost similar to those in precursor glasses. The intensity of frequency upconversion fluorescence at around 550 nm due to the ⁴ S₃₁₂→⁴I₁₅₁₂ transition of Er³⁺ in the glass ceramics is strong compared with that in their precursor glass. From the phonon sideband spectra associated with ⁵D₂→⁷F₀ transition of Eu³⁺ it is found that the phonon energy for transparent glass ceramics is smaller than that in the glasses, indicating that the multiphonon relaxation rate of Er³⁺ and Eu³⁺ present in TeO² based glass ceramics is smaller than that in the corresponding TeO₂ based glasses. Whether Er³⁺ and Eu³⁺ are incorporated into the crystalline phase or not is unclear the present study gives a new possibility for optical applications of transparent TeO₂ based glass ceramics.