Absorption and upconversion light emission properties of Er 3+ and Yb 3+/Er 3+ codoped NaYS 2

Abstract

The upconversion properties of Er 3+ doped and Yb 3+/Er 3+ codoped NaYS 2 crystals are presented. Under near-IR excitation around 10 000 cm −1 intense upconversion emission from the Er 3+ 4F 7/2, 4S 3/2, 4F 9/2 and 4I 9/2 excited states is observed at 12 K. A favorable green 4S 3/2 to red 4F 9/2 photon ratio of 8 is observed in Er 3+ doped NaYS 2. Low lying S 2− to Yb 3+ ligand to metal charge transfer transitions interact with Er 3+ emitting states in Yb 3+/Er 3+ codoped NaYS 2 and essentially quench the green emission. In contrast to many oxide and halide materials, Yb 3+ is not a suitable sensitizer for Er 3+ UC emission in this sulfide host lattice.