Upconversion emission and second harmonic generation of the YVO₄: Tm³⁺, Er³⁺, Yb³⁺ inverse opals

The YVO₄:Tm³⁺, Er³⁺, Yb³⁺ nanomaterials were fabricated with a simple chemical method. The X-ray diffraction, scanning electron microscopy and transmission electron microscopy characterizations confirm that the YVO₄:Tm³⁺, Er³⁺, Yb³⁺ nanomaterials have good structure with the polycrystalline. With the excitation of the 975 nm laser, the white color emissions were observed in the YVO₄:Tm³⁺, Er³⁺, Yb³⁺ inverse opals with the polystyrene (PS) size of 450 nm and the composition of Y:Tm:Er:Yb = 77.5:0.5:2:20, in which the blue emission is the second harmonic generation (SHG) signal of the incident laser. The inverse opals have great effect on the upconversion emission and the SHG signal. With the inverse opal structures the blue SHG signal increases significantly for the inverse opals with the PS size of 250 and 450 nm, in which the SHG signal of the inverse opal with the PS size of 450 nm is stronger and is more suitable for the white emission due to the narrow width of the SHG signal. The power dependencies confirm that the upconversion emissions have the slope factor of 2–3, which means that the upconversion processes are the three-photon processes.