Fluoride and tellurite glasses for thin-film IR viewers

We have studied optical characteristics of Er³⁺-, Ho³⁺-, and Yb³⁺-doped ZBLAN and TWL glasses. Their luminescence was excited at wavelengths of 975, 378, and 449 nm. The 975-nm radiation excited the Yb³⁺ (² F _7/2 → ² F _5/2), and the excitation energy was then transferred to the Er³⁺ and Ho³⁺. The short-wavelength excitation led to cross-relaxation processes: (⁴ F _7/2, ² F _7/2) → (⁴ I _11/2, ² F _5/2) for the Er³⁺-Yb³⁺ pair (378 nm) and (⁵ F ₃, ² F _7/2) → (⁵ I ₅, ² F _5/2) for the Ho³⁺-Yb³⁺ (449 nm). At the three excitation wavelengths, we observed green luminescence in the range 525–550 nm. Using the glasses studied here, we prepared thin colorless lacquer films potentially attractive for hidden information recording and hidden labeling of various objects and materials.