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

The ZnS: Ho 3+ , Yb 3+ , Mn 2+ 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 Mn 2+ has less effect on the structure of the ZnS: Ho 3+ , Yb 3+ , Mn 2+ nanomaterials. With the excitation of a 978 nm laser, the upconversion (UC) emissions of the ZnS: Ho 3+ , Yb 3+ , Mn 2+ nanomaterials include two emission bands located at 551 and 664 nm, which correspond to the transitions 5 F 4 ( 5 S 2 )→ 5 I 8 and 5 F 5 → 5 I 8 of the Ho 3+ ions. The UC emission characterization confirms that the UC emission of the ZnS: Ho 3+ , Yb 3+ nanomaterials can be modulated by the doping of the Mn 2+ ions, the increase of the incident laser power and the change of the laser pulse-width. The red emission of the ZnS: Ho 3+ , Yb 3+ nanomaterials particle will increase significantly with the incorporation of the Mn 2+ 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 5 F 4 ( 5 S 2 ) state to the 5 F 5 state of the Ho 3+ ions through the state 4 T 1 of the Mn 2+ ions.