Narrow line spectra induced by Er³⁺ in silica glasses containing SnO₂ nanocrystals

Silica glasses containing SnO₂ nanocrystals and Er³⁺ ions were prepared by the sol-gel route and proper annealing treatments. A few samples were prepared with fluorinated Si precursors. Er³⁺ transitions from the ground ⁴I_15/2 to the ⁴I_13/2, ⁴I_11/2, ⁴I _9/2, ⁴F_9/2, ⁴S_3/2, ²H_11/2, and ⁴F_7/2 excited manifolds were monitored by means of high resolution (as fine as 0.1 cm^-1) Fourier Transform spectroscopy in the wave number (6000-22000 cm^-1) and temperature (9-300 K) range, respectively. Broad absorption spectra were observed in silica samples simply doped with Er³⁺, as expected for Er³⁺ in a glassy environment. In samples containing also SnO ₂ nanocrystals, complex, narrow line Er³⁺ related spectra were monitored. The lines become sharper and sharper by lowering the temperature to 9 K, as expected for Er³⁺ ions embedded in an ordered (crystalline) environment. The nature and origin of different surroundings probed by the Er³⁺ line spectra are discussed.