Abstract of Publication No. 523
The upconversion properties of Er3+ doped and
Yb3+/Er3+ codoped NaYS2 crystals are presented.
Under near-IR excitation around 10 000 cm−1 intense upconversion
emission from the Er3+ 4F7/2,
4S3/2, 4F9/2 and
4I9/2 excited states is observed at 12 K. A favorable
green 4S3/2 to red 4F9/2 photon
ratio of 8 is observed in Er3+ doped NaYS2. Low lying
S2− to Yb3+ ligand to metal charge transfer transitions
interact with Er3+ emitting states in Yb3+/Er3+
codoped NaYS2 and essentially quench the green emission. In contrast
to many oxide and halide materials, Yb3+ is not a suitable sensitizer
for Er3+ UC emission in this sulfide host lattice.