Upconversion mechanism in Er3+-doped fluorozirconate glasses under 800 nm excitation

The upconversion emission intensities of ${\mathrm{Er}}^{\text{3+}}$ ion around 550 and 660 nm in fluorozirconate glasses were measured under 800 nm excitation. Though energy transfer processes played an important role in upconversion mechanism at high concentration of ${\mathrm{ErF}}_3,$ those have not been treated quantitatively. The energy transfer rates were calculated from the optical parameters assuming some distribution of ${\mathrm{Er}}^{\text{3+}}$ ions. We calculated the upconversion intensities around 550 and 660 nm by using rate equations. It was found that the dependence of upconversion emission intensities on the ${\mathrm{ErF}}_3$ concentration could be reproducible and the principal upconversion mechanism could be evaluated.