Xinghua Ma

Vacuum gap dependence of field electron emission properties of large area multi-walled carbon nanotube films

Field electron emission properties of aligned multi-walled carbon nanotube films were studied with variation of the vacuum gap d between anode and cathode. With d varying in the range of 0.4-2 mm, the emission current-gap voltage characteristics and the corresponding Fowler-Nordheim (FN) plots show distinct nonlinearity and regular changes with electrode separation. Three field enhancement factors may be derived from the three linear sections of a FN plot. Their variation with gap d results in different behaviours; significantly a drop of five times in the field enhancement factor is observed. The physical process responsible for our findings is suggested to be the space charge effect and both theoretical and experimental evidence is provided to support our arguments. The implication of our findings in technical applications is also discussed.

Optical properties of Pr3+: NaLa(WO4)2 single crystal

The polarized absorption spectra, polarized fluorescence spectra and fluorescence decay curve of Pr3+-doped NaLa(WO4)2 single crystals were measured at room temperature. The emission cross section has been presented and Judd–Ofelt theory has been applied to the analysis of the absorption spectra. The calculated radiative lifetime is compared with the experimental data for the 3P0 emitting level. The result indicates that the relaxation of the excited 3P0 level of praseodymium is governed by radiative transitions, which makes the 3P0 manifold of the Pr3+-doped NaLa(WO4)2 crystal promising as the upper laser level.