Polarization-Modified Upconversion Luminescence in Er-Doped Single-Crystal Perovskite PbTiO3 Nanofibers
journal contributionposted on 30.07.2015, 00:00 by Siyu Gong, Ming Li, Zhaohui Ren, Xin Yang, Xiang Li, Ge Shen, Gaorong Han
Understanding the energy transition which is influenced by doping ions and host materials in the upconversion (UC) physical processes is of vital importance for further optimizing performance and extending applications of UC materials. In this work, we have selected 4% Er-doped perovskite PbTiO3 (PTO) nanofibers as a model system to explore the effects of tetragonality and polarization on UC photoluminescence (PL) properties. By means of in situ X-ray diffraction, the tetragonality and polarization of these nanofibers have been determined to gradually decrease with an increasing of the temperature from 50 to 300 K, leading to obvious enhancements in UC green band emission of 523 nm (about 43 times) and red band emission of 656 nm (about 8 times), in contrast to the decreased green and red UC intensities in Er-doped BaTiO3 or PTO particles. Moreover, the significant enhancement in the intensity ratio of green to red bands from 0.17 to 0.86 has been achieved, indicating that the emission enhancement is highly wavelength-dependent. On the basis of in situ UC decay curves from 50 to 300 K, the UC lifetimes of the 4S3/2 and 4F9/2 level have been derived to be 128.04 ± 0.47 μs and 278.10 ± 1.07 μs at 50 K, respectively, and the values are basically maintained as the temperature increases. The observed UC phenomena in Er-doped perovskite PTO nanofibers can be ascribed to an assisted effect of the low-energy E(1TO) phonon on the UC process. Such phonon energy can be easily tailored by the tetragonality and polarization; thus, a modification of UC emissions in Er-doped PTO nanofibers has been achieved. The findings in this work could provide new insights into understanding the UC process in perovskite oxides and offer an opportunity to tune UC emission by an external field, such as an electric field, in addition to temperature.