The role of a three-ion energy transfer process in the violet fluorescence in highly doped Er:ZB(L)AN glasses

The violet (∼400-410-nm) fluorescence in Er³⁺:ZB(L)AN glasses has been previously attributed to transitions originating from the ²H_9/2 and ²P_3/2 levels. The study reported here found that, in high Er³⁺ concentrations and with 800-nm excitation, a significant source of violet fluorescence around 407-nm was due to the previously unreported ⁴G_9/2 → ⁴I_9/2 transition. The study also established that, under these conditions, a three-ion energy transfer process originating in the ⁴I_9/2 level is responsible for populating of the fluorescing ⁴G_9/2 level.