Enhanced downconversion luminescence of NaLuF4:Yb3+,Er3+ micrometer hexagonal prismatic crystals under 980 nm excitation

Abstract

NaLuF4:Yb3+,Er3+ micrometer prismatic crystals are potential materials for the preparation of optical waveguide devices. However, structural defects and OH– groups are generated inside and on their surfaces during growth processes. The structural defects and OH– groups lead to a large depletion of excitation energy and severely quench the downconversion luminescence of Er3+. In addition, the Yb3+/Er3+ co-doping ratio significantly affects the downconversion luminescence of the microcrystals, which in turn affects the performance of the optical waveguide amplifiers based on the microcrystals. By adjusting the co-doping ratio of Yb3+ and Er3+ in the microcrystals and removing the defects in the crystals, their downconversion luminescence performance was significantly improved. The results showed that the downconversion luminescence under the excitation from a 980 nm laser reached the maximum value when the doping ratio of Yb3+ and Er3+ was 20:1.5. In addition, the OH– groups and structural defects in the micrometer crystals were significantly eliminated by ion-exchange and high-temperature annealing treatments, and the crystalline quality was significantly improved. After ion-exchange and high-temperature annealing treatments, the downconversion luminescence enhancement of NaLuF4:Yb3+,Er3+ microcrystals was 2.5 times that of the untreated samples.