Transparent surface and bulk crystallized glasses with lanthanide tellurite nanocrystals

Crystallization behavior of BaO-Ln₂O₃-TeO₂ glasses (Ln = La, Pr, Sm, Eu, Er) was examined to prepare transparent crystallized glasses consisting of lanthanide tellurite crystals (Te⁴⁺ crystalline compounds) with low phonon energies. Transparent crystallized glasses with fluorite-type Ln₂Te₆O₁₅ or Ln₂Te₅O₁₃ nanocrystals (∼50 nm sizes) were successfully prepared for the first time. The crystallization mechanism depends strongly on the lanthanide species: surface crystallization (∼15 μm) is dominant in La³⁺ and Pr³⁺ containing glasses, but homogeneous nucleation occurs easily in Sm³⁺, Eu³⁺ and Er³⁺ containing glasses, giving transparent bulk crystallized glasses. These transparent nano-crystallized glasses are applicable to fabrication of optical amplified waveguides or Bragg grating fibers.