Near infrared to visible upconversion photoluminescence from Er/Yb co-doped MoS2 nanosheets with tunable thickness

Abstract

Er/Yb co-doped MoS2 nanosheets exhibit efficient upconversion photoluminescence emission in the visible wavelength region at 524 nm, 541 nm, 650 nm and downconversion emission at 1124 nm under the excitation of 980 nm laser. These upconversion and downconversion emissions are proposed to be due to the 2H11/2 - 4I15/2 (524 nm), 4S3/2 - 4I15/2 (541 nm), 4F9/2 - 4I15/2 (650 nm) transitions of Er3+ and 2F5/2 → 2F7/2 (1124 nm) transition of Yb3+ ions respectively. It is also found that the Yb3+ ions play a significant role as a sensitizer for the generation of visible upconversion emission of Er3+ ions via excited state energy transfer mechanism. Further, the effects of the layer numbers in co-doped MoS2 on the upconversion photoluminescence properties are also evaluated. The MoS2 nanosheet possessing more number of layers fascinates stronger emission intensities due to the predominant crystal field effect.