Influence of Zn2+ ions concentration on the optical properties of Zn/Er:LiNbO3 crystals

Congruent Er³⁺(3 mol%):LiNbO₃ crystals codoped with ZnO (X mol %, X=0, 3, 6 and 7) were grown by the Czochralski technique. The Er contents in the crystals were measured by an inductively coupled plasma atomic emission spectrometer (ICP‐AES). Under 800 nm excitation, the upconversion emission spectra reveal an enhancement of the green emission with respect to the red emission when the Zn²⁺ ions are introduced into Er:LiNbO₃ crystal. The effect of Zn²⁺ ions concentration on the intensity ratio of the green to red emission has been investigated. Two cross‐relaxation processes (²H_11/2 + ⁴I_13/2 → ⁴I_11/2 + ⁴F_9/2 and ⁴F_7/2 + ⁴I_11/2 → ⁴F_9/2 + ⁴F_9/2) are involved in populating the ⁴F_9/2 state, which bypass the green‐emitting states. The OH^‐ absorption spectra indicate that the Zn²⁺ codoping leads to a decreased concentration of Er³⁺ cluster sites contributing to the enhancement of the green emission. The studies on UV‐vis absorption spectra show that the heavily codoped with Zn²⁺ results in the reformation of the Er³⁺ cluster sites in Er:LiNbO₃. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)