Synthesis of Yb3+, Ho3+ and Tm3+ co-doped β-NaYF4 nanoparticles by sol–gel method and the multi-color upconversion luminescence properties

Well-crystalline β-NaYF4:Yb3+, Ho3+, Tm3+ nanoparticles were synthesized by sol–gel method using isopropyl alcohol [(CH3)2CHOH] as a complexing agent. The samples were characterized by X-ray diffraction, scanning electron microscopic analysis and fluorescence spectrum analysis methods. Under the excitation of 980 nm laser diode (LD), the samples displayed bright upconversion luminescence (UCL), which was generated from the energy level transition of Ho3+ and Tm3+ ions. With the increase of Tm3+, Ho3+ and Yb3+-doping concentration, the UCL intensity of blue, green and red light emission of the samples varied. Calculation of the CIE color coordinate of the β-NaYF4:Yb3+, Ho3+, Tm3+ nanoparticles revealed that with the adjustment of Tm3+, Ho3+ and Yb3+ doping concentration and the excitation power of 980 nm LD, the multi-color UCL can be realized. Approximately single red light output with the CIE color coordinate of x = 0.545, y = 0.306 and white light output with the CIE color coordinate of x = 0.325, y = 0.320 can be obtained in the synthesized β-NaYF4: Yb3+, Ho3+, Tm3+ nanoparticles.