Influences of Mg^2＋ ion on dopant occupancy and upconversion luminescence of Ho^3＋ ion in LiNbO3 crystal

The effects of a Mg^2＋ ion on the dopant occupancy and upconversion luminescence of a Ho^3＋ ion in LiNbO3 crystal are reported. The birefringence gradient of the crystal is measured to investigate the optical homogeneity. The X-ray powder diffraction spectrum and the upconversion luminescence are used to investigate defect structure and spectroscopic properties of Mg,Ho：LiNbO3. Under 808-nm excitation, blue, red, and very intense yellow-green bands are observed. Based on the energy levels of Ho^3＋ in LiNbO3, and the pump intensity dependence of the observed emission, an excitation scheme is presented. The upconversion emission spectra reveal an enhancement of upconversion intensity when the Mg^2＋ ions are introduced into Ho：LiNbO3. The main upconversion mechanism is discussed in this work.