Rare earth doping into optical nonlinear nanocrystalline phase in transparent TeO₂-based glass-ceramics

Optically transparent rare earth (Ln)-doped glass-ceramics based on the system K₂O-Nb₂O₅-TeO₂ have been prepared, and the effect of Ln additions on crystallization behaviors and optical properties has been examined. The lattice constant of the TeO₂-based metastable optical nonlinear nanocrystalline phase (average particle size: <60nm) with basically a cubic structure in the glass-ceramics decreases due to Ln additions, and the incorporation of Ln³⁺ with small ionic radii such as Er³⁺ or Tm³⁺ stabilizes the metastable crystalline phase, giving the significant effect on the crystallization and phase transformation behaviors in TeO₂-based glasses. From the phonon sideband spectra associated with the ⁵D₀→⁷F₀ transition of Eu³⁺, it is found that both phonon energy and electron phonon coupling strength for transparent glass-ceramics are smaller than t hose in the precursor glass. The upconversion fluorescence intensity around 550 nm due to the ⁴S_3/2→⁴I_15/2 transition of Er³⁺ is strong (about 20 times) compared with the precursor glass.