Upconversion emission and its color modulation of the ZnS: Ho3+, Yb3+, Mn2+ nanomaterials

The ZnS: Ho3+, Yb3+, Mn2+ nanomaterials fabricated by the co-precipitation method have the zinc-blende structure with the crystallite size about 90 ∼ 100 nm. The X-ray diffraction (XRD), the scanning electron microscope (SEM) and the transmission electron microscope (TEM) characterizations confirm that the doping of the Mn2+ has less effect on the structure of the ZnS: Ho3+, Yb3+, Mn2+ nanomaterials. With the excitation of a 978 nm laser, the upconversion (UC) emissions of the ZnS: Ho3+, Yb3+, Mn2+ nanomaterials include two emission bands located at 551 and 664 nm, which correspond to the transitions 5F4 (5S2)→5I8 and 5F5→5I8 of the Ho3+ ions. The UC emission characterization confirms that the UC emission of the ZnS: Ho3+, Yb3+ nanomaterials can be modulated by the doping of the Mn2+ ions, the increase of the incident laser power and the change of the laser pulse-width. The red emission of the ZnS: Ho3+, Yb3+ nanomaterials particle will increase significantly with the incorporation of the Mn2+ ions. The incident laser power and the laser pulse-width also can modulate the intensity ratio G/R of the green to the red. With the increase of the incident laser power, the emission intensity ratio G/R will also increase. With the increase of laser pulse-width from 0.2 to 0.8 ms, the above intensity ratio G/R will decrease significantly. The modulation between the green and red emission is due to the energy transfer from the 5F4 (5S2) state to the 5F5 state of the Ho3+ ions through the state 4T1 of the Mn2+ ions.