Effect of Zn ²⁺ ions on upconversion emission of Er ³⁺ in Zn/Er:LiNbO ₃ crystal

The effect of Zn ²⁺ ions codoped on the upconversion emission of Er ³⁺ ions in Er:LiNbO ₃ crystal under different excitation wavelength was reported. The upconversion emission spectra of Zn/Er:LiNbO ₃ following 800 nm excitation reveal an enhanced green emission and a suppressed red emission simultaneously. The cross relaxation processes( ²H11/2+ ⁴I13/2→ ⁴I11/2+ ²F9/2 and ⁴F7/2+ ⁴I11/2→ ⁴F9/2+ ⁴F9/2) are responsible for populating the red ⁴F9/2 emitting state. The dissociation effect of Zn ²⁺ ions on the Er ³⁺ cluster sites makes these cross relaxation processes inefficient. Under 980 nm excitation, the Zn ²⁺ codoped leads to the decreased intensities of green and red upconversion emissions. These reductions are attributed to the inefficient cross relaxation processes( ⁴I11/2+ ⁴I11/2→ ⁴F7/2+ ⁴I15/2 and ⁴F7/2+4I11/2→ ⁴F9/2+ ⁴F9/2) caused by the same dissociation effect of Zn ²⁺ ions.