Sol-gel synthesis of β-NaYF4:Yb3+/Nd3+/Tm3+/Mn2+ nanophosphors and color-tunable upconversion luminescence

Highly crystalline β-NaYF4:Yb3+/Nd3+/Tm3+/Mn2+ nanophosphors were prepared by sol-gel methods with isopropyl alcohol as complexing agent. X-ray diffraction analysis data demonstrated that hexagonal phase β-NaYF4 was successfully synthesized by a calcination process on the as-prepared precursor at 550°C for 1h. Under a 980nm laser diode (LD) excitation, the samples demonstrated bright upconversion luminescence (UCL), which was caused by the energy level transition of Tm3+ and Nd3+ ions. With the increase of the doping concentration of Mn2+ ions, the UCL intensities in the blue light region increased firstly and then decreased, meanwhile, the UCL intensities in the red, yellow and green light region gradually increased. Color-tunable UCL of the sample was generated by the continuous variation of the pumping power of 980nm LD.