Upconversion properties, of Ln3+ doped NaYF4/polymer composite fibers prepared by electrospinning

Ln(3+) doped (Yb3+,Tm3+ codoped and Yb3+,Er3+,Tm3+ tridoped) NaYF4/poly(vinyl pyrrolidone)(PVP) (M-w approximate to 5 1300 000) composite fibers with an average diameter of 300-800 nm were prepared by electrospinning and characterized by X-ray diffraction, field emission scanning electron micrography, and Fourier transform infrared spectra. Their upconversion (UC) luminescence properties were studied in contrast to the corresponding Ln(3+) doped NaYF4 nanoparticles (15-20 nm) under 980-nm excitation. The results demonstrate that in the Yb3+,TM3+ codoped composite fibers the blue emission of (1)G(4)-H-1(6) is dominantly strong, while in the nanoparticles the red emission of F-3(2,3)-H-3(6) Contributes considerably to the increase of the excitation power. This indicates that the color purity of blue is improved greatly by the modification of PVP. In the tridoped Yb3+,Er3+, TM3+ composite fibers, white light with more stable color balance (blue (1)G(4)-H-3(6) of Tm3+, green H-2(11/2)/S-4(3/2)-I-4(15/2), and red F-4(9/2)-I-4(15/2) of Er3+) was obtained. The improved UC properties in the composite fibers are attributed to the suppressed local thermal effect. The energy transfer and UC populating processes are discussed.