Upconversion Properties of Ln3+ Doped NaYF4/Polymer Composite Fibers Prepared by Electrospinning

Ln 3+ doped (Yb 3+,Tm 3+ codoped and Yb 3+,Er 3+,Tm 3+ tridoped) NaYF 4 /poly(vinyl pyrrolidone)(PVP) ( M w ≈ 1 300 000) 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 NaYF 4 nanoparticles (15−20 nm) under 980-nm excitation. The results demonstrate that in the Yb 3+,Tm 3+ codoped composite fibers the blue emission of 1 G 4 - 3 H 6 is dominantly strong, while in the nanoparticles the red emission of 3 F 2,3 - 3 H 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 Yb 3+,Er 3+,Tm 3+ composite fibers, white light with more stable color balance (blue 1 G 4 - 3 H 6 of Tm 3+, green 2 H 11/2 / 4 S 3/2 - 4 I 15/2, and red 4 F 9/2 - 4 I 15/2 of Er 3+ ) 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.